Add formal support for alt text to IPython.display.Image.

For accessibility reasons users should be encouraged to add useful alt
text to images. Currently there is no recommended way to do this using
the standard Image object. Adding this field is a step towards getting
a common way for notebook renderers to support alt text and towards
encouraging libraries creating images to add meaningful alt text.

IPython/core/display.py

@@ -1,1211 +1,1223 b''
 # -*- coding: utf-8 -*-
 """Top-level display functions for displaying object in different formats."""
 
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
 
 from binascii import b2a_base64, hexlify
+import html
 import json
 import mimetypes
 import os
 import struct
 import warnings
 from copy import deepcopy
 from os.path import splitext
 from pathlib import Path, PurePath
 
 from IPython.utils.py3compat import cast_unicode
 from IPython.testing.skipdoctest import skip_doctest
 from . import display_functions
 
 
 __all__ = ['display_pretty', 'display_html', 'display_markdown',
            'display_svg', 'display_png', 'display_jpeg', 'display_latex', 'display_json',
            'display_javascript', 'display_pdf', 'DisplayObject', 'TextDisplayObject',
            'Pretty', 'HTML', 'Markdown', 'Math', 'Latex', 'SVG', 'ProgressBar', 'JSON',
            'GeoJSON', 'Javascript', 'Image', 'set_matplotlib_formats',
            'set_matplotlib_close',
            'Video']
 
 _deprecated_names = ["display", "clear_output", "publish_display_data", "update_display", "DisplayHandle"]
 
 __all__ = __all__ + _deprecated_names
 
 
 # ----- warn to import from IPython.display -----
 
 from warnings import warn
 
 
 def __getattr__(name):
     if name in _deprecated_names:
         warn(f"Importing {name} from IPython.core.display is deprecated since IPython 7.14, please import from IPython display", DeprecationWarning, stacklevel=2)
         return getattr(display_functions, name)
 
     if name in globals().keys():
         return globals()[name]
     else:
         raise AttributeError(f"module {__name__} has no attribute {name}")
 
 
 #-----------------------------------------------------------------------------
 # utility functions
 #-----------------------------------------------------------------------------
 
 def _safe_exists(path):
     """Check path, but don't let exceptions raise"""
     try:
         return os.path.exists(path)
     except Exception:
         return False
 
 
 def _display_mimetype(mimetype, objs, raw=False, metadata=None):
     """internal implementation of all display_foo methods
 
     Parameters
     ----------
     mimetype : str
         The mimetype to be published (e.g. 'image/png')
     *objs : object
         The Python objects to display, or if raw=True raw text data to
         display.
     raw : bool
         Are the data objects raw data or Python objects that need to be
         formatted before display? [default: False]
     metadata : dict (optional)
         Metadata to be associated with the specific mimetype output.
     """
     if metadata:
         metadata = {mimetype: metadata}
     if raw:
         # turn list of pngdata into list of { 'image/png': pngdata }
         objs = [ {mimetype: obj} for obj in objs ]
     display(*objs, raw=raw, metadata=metadata, include=[mimetype])
 
 #-----------------------------------------------------------------------------
 # Main functions
 #-----------------------------------------------------------------------------
 
 
 def display_pretty(*objs, **kwargs):
     """Display the pretty (default) representation of an object.
 
     Parameters
     ----------
     *objs : object
         The Python objects to display, or if raw=True raw text data to
         display.
     raw : bool
         Are the data objects raw data or Python objects that need to be
         formatted before display? [default: False]
     metadata : dict (optional)
         Metadata to be associated with the specific mimetype output.
     """
     _display_mimetype('text/plain', objs, **kwargs)
 
 
 def display_html(*objs, **kwargs):
     """Display the HTML representation of an object.
 
     Note: If raw=False and the object does not have a HTML
     representation, no HTML will be shown.
 
     Parameters
     ----------
     *objs : object
         The Python objects to display, or if raw=True raw HTML data to
         display.
     raw : bool
         Are the data objects raw data or Python objects that need to be
         formatted before display? [default: False]
     metadata : dict (optional)
         Metadata to be associated with the specific mimetype output.
     """
     _display_mimetype('text/html', objs, **kwargs)
 
 
 def display_markdown(*objs, **kwargs):
     """Displays the Markdown representation of an object.
 
     Parameters
     ----------
     *objs : object
         The Python objects to display, or if raw=True raw markdown data to
         display.
     raw : bool
         Are the data objects raw data or Python objects that need to be
         formatted before display? [default: False]
     metadata : dict (optional)
         Metadata to be associated with the specific mimetype output.
     """
 
     _display_mimetype('text/markdown', objs, **kwargs)
 
 
 def display_svg(*objs, **kwargs):
     """Display the SVG representation of an object.
 
     Parameters
     ----------
     *objs : object
         The Python objects to display, or if raw=True raw svg data to
         display.
     raw : bool
         Are the data objects raw data or Python objects that need to be
         formatted before display? [default: False]
     metadata : dict (optional)
         Metadata to be associated with the specific mimetype output.
     """
     _display_mimetype('image/svg+xml', objs, **kwargs)
 
 
 def display_png(*objs, **kwargs):
     """Display the PNG representation of an object.
 
     Parameters
     ----------
     *objs : object
         The Python objects to display, or if raw=True raw png data to
         display.
     raw : bool
         Are the data objects raw data or Python objects that need to be
         formatted before display? [default: False]
     metadata : dict (optional)
         Metadata to be associated with the specific mimetype output.
     """
     _display_mimetype('image/png', objs, **kwargs)
 
 
 def display_jpeg(*objs, **kwargs):
     """Display the JPEG representation of an object.
 
     Parameters
     ----------
     *objs : object
         The Python objects to display, or if raw=True raw JPEG data to
         display.
     raw : bool
         Are the data objects raw data or Python objects that need to be
         formatted before display? [default: False]
     metadata : dict (optional)
         Metadata to be associated with the specific mimetype output.
     """
     _display_mimetype('image/jpeg', objs, **kwargs)
 
 
 def display_latex(*objs, **kwargs):
     """Display the LaTeX representation of an object.
 
     Parameters
     ----------
     *objs : object
         The Python objects to display, or if raw=True raw latex data to
         display.
     raw : bool
         Are the data objects raw data or Python objects that need to be
         formatted before display? [default: False]
     metadata : dict (optional)
         Metadata to be associated with the specific mimetype output.
     """
     _display_mimetype('text/latex', objs, **kwargs)
 
 
 def display_json(*objs, **kwargs):
     """Display the JSON representation of an object.
 
     Note that not many frontends support displaying JSON.
 
     Parameters
     ----------
     *objs : object
         The Python objects to display, or if raw=True raw json data to
         display.
     raw : bool
         Are the data objects raw data or Python objects that need to be
         formatted before display? [default: False]
     metadata : dict (optional)
         Metadata to be associated with the specific mimetype output.
     """
     _display_mimetype('application/json', objs, **kwargs)
 
 
 def display_javascript(*objs, **kwargs):
     """Display the Javascript representation of an object.
 
     Parameters
     ----------
     *objs : object
         The Python objects to display, or if raw=True raw javascript data to
         display.
     raw : bool
         Are the data objects raw data or Python objects that need to be
         formatted before display? [default: False]
     metadata : dict (optional)
         Metadata to be associated with the specific mimetype output.
     """
     _display_mimetype('application/javascript', objs, **kwargs)
 
 
 def display_pdf(*objs, **kwargs):
     """Display the PDF representation of an object.
 
     Parameters
     ----------
     *objs : object
         The Python objects to display, or if raw=True raw javascript data to
         display.
     raw : bool
         Are the data objects raw data or Python objects that need to be
         formatted before display? [default: False]
     metadata : dict (optional)
         Metadata to be associated with the specific mimetype output.
     """
     _display_mimetype('application/pdf', objs, **kwargs)
 
 
 #-----------------------------------------------------------------------------
 # Smart classes
 #-----------------------------------------------------------------------------
 
 
 class DisplayObject(object):
     """An object that wraps data to be displayed."""
 
     _read_flags = 'r'
     _show_mem_addr = False
     metadata = None
 
     def __init__(self, data=None, url=None, filename=None, metadata=None):
         """Create a display object given raw data.
 
         When this object is returned by an expression or passed to the
         display function, it will result in the data being displayed
         in the frontend. The MIME type of the data should match the
         subclasses used, so the Png subclass should be used for 'image/png'
         data. If the data is a URL, the data will first be downloaded
         and then displayed. If
 
         Parameters
         ----------
         data : unicode, str or bytes
             The raw data or a URL or file to load the data from
         url : unicode
             A URL to download the data from.
         filename : unicode
             Path to a local file to load the data from.
         metadata : dict
             Dict of metadata associated to be the object when displayed
         """
         if isinstance(data, (Path, PurePath)):
             data = str(data)
 
         if data is not None and isinstance(data, str):
             if data.startswith('http') and url is None:
                 url = data
                 filename = None
                 data = None
             elif _safe_exists(data) and filename is None:
                 url = None
                 filename = data
                 data = None
 
         self.url = url
         self.filename = filename
         # because of @data.setter methods in
         # subclasses ensure url and filename are set
         # before assigning to self.data
         self.data = data
 
         if metadata is not None:
             self.metadata = metadata
         elif self.metadata is None:
             self.metadata = {}
 
         self.reload()
         self._check_data()
 
     def __repr__(self):
         if not self._show_mem_addr:
             cls = self.__class__
             r = "<%s.%s object>" % (cls.__module__, cls.__name__)
         else:
             r = super(DisplayObject, self).__repr__()
         return r
 
     def _check_data(self):
         """Override in subclasses if there's something to check."""
         pass
 
     def _data_and_metadata(self):
         """shortcut for returning metadata with shape information, if defined"""
         if self.metadata:
             return self.data, deepcopy(self.metadata)
         else:
             return self.data
 
     def reload(self):
         """Reload the raw data from file or URL."""
         if self.filename is not None:
             with open(self.filename, self._read_flags) as f:
                 self.data = f.read()
         elif self.url is not None:
             # Deferred import
             from urllib.request import urlopen
             response = urlopen(self.url)
             data = response.read()
             # extract encoding from header, if there is one:
             encoding = None
             if 'content-type' in response.headers:
                 for sub in response.headers['content-type'].split(';'):
                     sub = sub.strip()
                     if sub.startswith('charset'):
                         encoding = sub.split('=')[-1].strip()
                         break
             if 'content-encoding' in response.headers:
                 # TODO: do deflate?
                 if 'gzip' in response.headers['content-encoding']:
                     import gzip
                     from io import BytesIO
                     with gzip.open(BytesIO(data), 'rt', encoding=encoding) as fp:
                         encoding = None
                         data = fp.read()
                     
             # decode data, if an encoding was specified
             # We only touch self.data once since
             # subclasses such as SVG have @data.setter methods
             # that transform self.data into ... well svg.
             if encoding:
                 self.data = data.decode(encoding, 'replace')
             else:
                 self.data = data
 
 
 class TextDisplayObject(DisplayObject):
     """Validate that display data is text"""
     def _check_data(self):
         if self.data is not None and not isinstance(self.data, str):
             raise TypeError("%s expects text, not %r" % (self.__class__.__name__, self.data))
 
 class Pretty(TextDisplayObject):
 
     def _repr_pretty_(self, pp, cycle):
         return pp.text(self.data)
 
 
 class HTML(TextDisplayObject):
 
     def __init__(self, data=None, url=None, filename=None, metadata=None):
         def warn():
             if not data:
                 return False
 
             #
             # Avoid calling lower() on the entire data, because it could be a
             # long string and we're only interested in its beginning and end.
             #
             prefix = data[:10].lower()
             suffix = data[-10:].lower()
             return prefix.startswith("<iframe ") and suffix.endswith("</iframe>")
 
         if warn():
             warnings.warn("Consider using IPython.display.IFrame instead")
         super(HTML, self).__init__(data=data, url=url, filename=filename, metadata=metadata)
 
     def _repr_html_(self):
         return self._data_and_metadata()
 
     def __html__(self):
         """
         This method exists to inform other HTML-using modules (e.g. Markupsafe,
         htmltag, etc) that this object is HTML and does not need things like
         special characters (<>&) escaped.
         """
         return self._repr_html_()
 
 
 class Markdown(TextDisplayObject):
 
     def _repr_markdown_(self):
         return self._data_and_metadata()
 
 
 class Math(TextDisplayObject):
 
     def _repr_latex_(self):
         s = r"$\displaystyle %s$" % self.data.strip('$')
         if self.metadata:
             return s, deepcopy(self.metadata)
         else:
             return s
 
 
 class Latex(TextDisplayObject):
 
     def _repr_latex_(self):
         return self._data_and_metadata()
 
 
 class SVG(DisplayObject):
     """Embed an SVG into the display.
 
     Note if you just want to view a svg image via a URL use `:class:Image` with
     a url=URL keyword argument.
     """
 
     _read_flags = 'rb'
     # wrap data in a property, which extracts the <svg> tag, discarding
     # document headers
     _data = None
 
     @property
     def data(self):
         return self._data
 
     @data.setter
     def data(self, svg):
         if svg is None:
             self._data = None
             return
         # parse into dom object
         from xml.dom import minidom
         x = minidom.parseString(svg)
         # get svg tag (should be 1)
         found_svg = x.getElementsByTagName('svg')
         if found_svg:
             svg = found_svg[0].toxml()
         else:
             # fallback on the input, trust the user
             # but this is probably an error.
             pass
         svg = cast_unicode(svg)
         self._data = svg
 
     def _repr_svg_(self):
         return self._data_and_metadata()
 
 class ProgressBar(DisplayObject):
     """Progressbar supports displaying a progressbar like element
     """
     def __init__(self, total):
         """Creates a new progressbar
 
         Parameters
         ----------
         total : int
             maximum size of the progressbar
         """
         self.total = total
         self._progress = 0
         self.html_width = '60ex'
         self.text_width = 60
         self._display_id = hexlify(os.urandom(8)).decode('ascii')
 
     def __repr__(self):
         fraction = self.progress / self.total
         filled = '=' * int(fraction * self.text_width)
         rest = ' ' * (self.text_width - len(filled))
         return '[{}{}] {}/{}'.format(
             filled, rest,
             self.progress, self.total,
         )
 
     def _repr_html_(self):
         return "<progress style='width:{}' max='{}' value='{}'></progress>".format(
             self.html_width, self.total, self.progress)
 
     def display(self):
         display(self, display_id=self._display_id)
 
     def update(self):
         display(self, display_id=self._display_id, update=True)
 
     @property
     def progress(self):
         return self._progress
 
     @progress.setter
     def progress(self, value):
         self._progress = value
         self.update()
 
     def __iter__(self):
         self.display()
         self._progress = -1 # First iteration is 0
         return self
 
     def __next__(self):
         """Returns current value and increments display by one."""
         self.progress += 1
         if self.progress < self.total:
             return self.progress
         else:
             raise StopIteration()
 
 class JSON(DisplayObject):
     """JSON expects a JSON-able dict or list
 
     not an already-serialized JSON string.
 
     Scalar types (None, number, string) are not allowed, only dict or list containers.
     """
     # wrap data in a property, which warns about passing already-serialized JSON
     _data = None
     def __init__(self, data=None, url=None, filename=None, expanded=False, metadata=None, root='root', **kwargs):
         """Create a JSON display object given raw data.
 
         Parameters
         ----------
         data : dict or list
             JSON data to display. Not an already-serialized JSON string.
             Scalar types (None, number, string) are not allowed, only dict
             or list containers.
         url : unicode
             A URL to download the data from.
         filename : unicode
             Path to a local file to load the data from.
         expanded : boolean
             Metadata to control whether a JSON display component is expanded.
         metadata : dict
             Specify extra metadata to attach to the json display object.
         root : str
             The name of the root element of the JSON tree
         """
         self.metadata = {
             'expanded': expanded,
             'root': root,
         }
         if metadata:
             self.metadata.update(metadata)
         if kwargs:
             self.metadata.update(kwargs)
         super(JSON, self).__init__(data=data, url=url, filename=filename)
 
     def _check_data(self):
         if self.data is not None and not isinstance(self.data, (dict, list)):
             raise TypeError("%s expects JSONable dict or list, not %r" % (self.__class__.__name__, self.data))
 
     @property
     def data(self):
         return self._data
 
     @data.setter
     def data(self, data):
         if isinstance(data, (Path, PurePath)):
             data = str(data)
 
         if isinstance(data, str):
             if self.filename is None and self.url is None:
                 warnings.warn("JSON expects JSONable dict or list, not JSON strings")
             data = json.loads(data)
         self._data = data
 
     def _data_and_metadata(self):
         return self.data, self.metadata
 
     def _repr_json_(self):
         return self._data_and_metadata()
 
 _css_t = """var link = document.createElement("link");
 	link.ref = "stylesheet";
 	link.type = "text/css";
 	link.href = "%s";
 	document.head.appendChild(link);
 """
 
 _lib_t1 = """new Promise(function(resolve, reject) {
 	var script = document.createElement("script");
 	script.onload = resolve;
 	script.onerror = reject;
 	script.src = "%s";
 	document.head.appendChild(script);
 }).then(() => {
 """
 
 _lib_t2 = """
 });"""
 
 class GeoJSON(JSON):
     """GeoJSON expects JSON-able dict
 
     not an already-serialized JSON string.
 
     Scalar types (None, number, string) are not allowed, only dict containers.
     """
 
     def __init__(self, *args, **kwargs):
         """Create a GeoJSON display object given raw data.
 
         Parameters
         ----------
         data : dict or list
             VegaLite data. Not an already-serialized JSON string.
             Scalar types (None, number, string) are not allowed, only dict
             or list containers.
         url_template : string
             Leaflet TileLayer URL template: http://leafletjs.com/reference.html#url-template
         layer_options : dict
             Leaflet TileLayer options: http://leafletjs.com/reference.html#tilelayer-options
         url : unicode
             A URL to download the data from.
         filename : unicode
             Path to a local file to load the data from.
         metadata : dict
             Specify extra metadata to attach to the json display object.
 
         Examples
         --------
         The following will display an interactive map of Mars with a point of
         interest on frontend that do support GeoJSON display.
 
             >>> from IPython.display import GeoJSON
 
             >>> GeoJSON(data={
             ...     "type": "Feature",
             ...     "geometry": {
             ...         "type": "Point",
             ...         "coordinates": [-81.327, 296.038]
             ...     }
             ... },
             ... url_template="http://s3-eu-west-1.amazonaws.com/whereonmars.cartodb.net/{basemap_id}/{z}/{x}/{y}.png",
             ... layer_options={
             ...     "basemap_id": "celestia_mars-shaded-16k_global",
             ...     "attribution" : "Celestia/praesepe",
             ...     "minZoom" : 0,
             ...     "maxZoom" : 18,
             ... })
             <IPython.core.display.GeoJSON object>
 
         In the terminal IPython, you will only see the text representation of
         the GeoJSON object.
 
         """
 
         super(GeoJSON, self).__init__(*args, **kwargs)
 
 
     def _ipython_display_(self):
         bundle = {
             'application/geo+json': self.data,
             'text/plain': '<IPython.display.GeoJSON object>'
         }
         metadata = {
             'application/geo+json': self.metadata
         }
         display(bundle, metadata=metadata, raw=True)
 
 class Javascript(TextDisplayObject):
 
     def __init__(self, data=None, url=None, filename=None, lib=None, css=None):
         """Create a Javascript display object given raw data.
 
         When this object is returned by an expression or passed to the
         display function, it will result in the data being displayed
         in the frontend. If the data is a URL, the data will first be
         downloaded and then displayed.
 
         In the Notebook, the containing element will be available as `element`,
         and jQuery will be available.  Content appended to `element` will be
         visible in the output area.
 
         Parameters
         ----------
         data : unicode, str or bytes
             The Javascript source code or a URL to download it from.
         url : unicode
             A URL to download the data from.
         filename : unicode
             Path to a local file to load the data from.
         lib : list or str
             A sequence of Javascript library URLs to load asynchronously before
             running the source code. The full URLs of the libraries should
             be given. A single Javascript library URL can also be given as a
             string.
         css : list or str
             A sequence of css files to load before running the source code.
             The full URLs of the css files should be given. A single css URL
             can also be given as a string.
         """
         if isinstance(lib, str):
             lib = [lib]
         elif lib is None:
             lib = []
         if isinstance(css, str):
             css = [css]
         elif css is None:
             css = []
         if not isinstance(lib, (list,tuple)):
             raise TypeError('expected sequence, got: %r' % lib)
         if not isinstance(css, (list,tuple)):
             raise TypeError('expected sequence, got: %r' % css)
         self.lib = lib
         self.css = css
         super(Javascript, self).__init__(data=data, url=url, filename=filename)
 
     def _repr_javascript_(self):
         r = ''
         for c in self.css:
             r += _css_t % c
         for l in self.lib:
             r += _lib_t1 % l
         r += self.data
         r += _lib_t2*len(self.lib)
         return r
 
 # constants for identifying png/jpeg data
 _PNG = b'\x89PNG\r\n\x1a\n'
 _JPEG = b'\xff\xd8'
 
 def _pngxy(data):
     """read the (width, height) from a PNG header"""
     ihdr = data.index(b'IHDR')
     # next 8 bytes are width/height
     return struct.unpack('>ii', data[ihdr+4:ihdr+12])
 
 def _jpegxy(data):
     """read the (width, height) from a JPEG header"""
     # adapted from http://www.64lines.com/jpeg-width-height
 
     idx = 4
     while True:
         block_size = struct.unpack('>H', data[idx:idx+2])[0]
         idx = idx + block_size
         if data[idx:idx+2] == b'\xFF\xC0':
             # found Start of Frame
             iSOF = idx
             break
         else:
             # read another block
             idx += 2
 
     h, w = struct.unpack('>HH', data[iSOF+5:iSOF+9])
     return w, h
 
 def _gifxy(data):
     """read the (width, height) from a GIF header"""
     return struct.unpack('<HH', data[6:10])
 
 
 class Image(DisplayObject):
 
     _read_flags = 'rb'
     _FMT_JPEG = u'jpeg'
     _FMT_PNG = u'png'
     _FMT_GIF = u'gif'
     _ACCEPTABLE_EMBEDDINGS = [_FMT_JPEG, _FMT_PNG, _FMT_GIF]
     _MIMETYPES = {
         _FMT_PNG: 'image/png',
         _FMT_JPEG: 'image/jpeg',
         _FMT_GIF: 'image/gif',
     }
 
     def __init__(self, data=None, url=None, filename=None, format=None,
                  embed=None, width=None, height=None, retina=False,
-                 unconfined=False, metadata=None):
+                 unconfined=False, metadata=None, alt=None):
         """Create a PNG/JPEG/GIF image object given raw data.
 
         When this object is returned by an input cell or passed to the
         display function, it will result in the image being displayed
         in the frontend.
 
         Parameters
         ----------
         data : unicode, str or bytes
             The raw image data or a URL or filename to load the data from.
             This always results in embedded image data.
         url : unicode
             A URL to download the data from. If you specify `url=`,
             the image data will not be embedded unless you also specify `embed=True`.
         filename : unicode
             Path to a local file to load the data from.
             Images from a file are always embedded.
         format : unicode
             The format of the image data (png/jpeg/jpg/gif). If a filename or URL is given
             for format will be inferred from the filename extension.
         embed : bool
             Should the image data be embedded using a data URI (True) or be
             loaded using an <img> tag. Set this to True if you want the image
             to be viewable later with no internet connection in the notebook.
 
             Default is `True`, unless the keyword argument `url` is set, then
             default value is `False`.
 
             Note that QtConsole is not able to display images if `embed` is set to `False`
         width : int
             Width in pixels to which to constrain the image in html
         height : int
             Height in pixels to which to constrain the image in html
         retina : bool
             Automatically set the width and height to half of the measured
             width and height.
             This only works for embedded images because it reads the width/height
             from image data.
             For non-embedded images, you can just set the desired display width
             and height directly.
         unconfined : bool
             Set unconfined=True to disable max-width confinement of the image.
         metadata : dict
             Specify extra metadata to attach to the image.
+        alt : unicode
+            Alternative text for the image, for use by screen readers.
 
         Examples
         --------
         embedded image data, works in qtconsole and notebook
         when passed positionally, the first arg can be any of raw image data,
         a URL, or a filename from which to load image data.
         The result is always embedding image data for inline images.
 
         >>> Image('http://www.google.fr/images/srpr/logo3w.png')
         <IPython.core.display.Image object>
 
         >>> Image('/path/to/image.jpg')
         <IPython.core.display.Image object>
 
         >>> Image(b'RAW_PNG_DATA...')
         <IPython.core.display.Image object>
 
         Specifying Image(url=...) does not embed the image data,
         it only generates ``<img>`` tag with a link to the source.
         This will not work in the qtconsole or offline.
 
         >>> Image(url='http://www.google.fr/images/srpr/logo3w.png')
         <IPython.core.display.Image object>
 
         """
         if isinstance(data, (Path, PurePath)):
             data = str(data)
 
         if filename is not None:
             ext = self._find_ext(filename)
         elif url is not None:
             ext = self._find_ext(url)
         elif data is None:
             raise ValueError("No image data found. Expecting filename, url, or data.")
         elif isinstance(data, str) and (
             data.startswith('http') or _safe_exists(data)
         ):
             ext = self._find_ext(data)
         else:
             ext = None
 
         if format is None:
             if ext is not None:
                 if ext == u'jpg' or ext == u'jpeg':
                     format = self._FMT_JPEG
                 elif ext == u'png':
                     format = self._FMT_PNG
                 elif ext == u'gif':
                     format = self._FMT_GIF
                 else:
                     format = ext.lower()
             elif isinstance(data, bytes):
                 # infer image type from image data header,
                 # only if format has not been specified.
                 if data[:2] == _JPEG:
                     format = self._FMT_JPEG
 
         # failed to detect format, default png
         if format is None:
             format = self._FMT_PNG
 
         if format.lower() == 'jpg':
             # jpg->jpeg
             format = self._FMT_JPEG
 
         self.format = format.lower()
         self.embed = embed if embed is not None else (url is None)
 
         if self.embed and self.format not in self._ACCEPTABLE_EMBEDDINGS:
             raise ValueError("Cannot embed the '%s' image format" % (self.format))
         if self.embed:
             self._mimetype = self._MIMETYPES.get(self.format)
 
         self.width = width
         self.height = height
         self.retina = retina
         self.unconfined = unconfined
+        self.alt = alt
         super(Image, self).__init__(data=data, url=url, filename=filename,
                 metadata=metadata)
 
         if self.width is None and self.metadata.get('width', {}):
             self.width = metadata['width']
 
         if self.height is None and self.metadata.get('height', {}):
             self.height = metadata['height']
 
+        if self.alt is None and self.metadata.get('alt', {}):
+            self.alt = metadata['alt']
+
         if retina:
             self._retina_shape()
 
 
     def _retina_shape(self):
         """load pixel-doubled width and height from image data"""
         if not self.embed:
             return
         if self.format == self._FMT_PNG:
             w, h = _pngxy(self.data)
         elif self.format == self._FMT_JPEG:
             w, h = _jpegxy(self.data)
         elif self.format == self._FMT_GIF:
             w, h = _gifxy(self.data)
         else:
             # retina only supports png
             return
         self.width = w // 2
         self.height = h // 2
 
     def reload(self):
         """Reload the raw data from file or URL."""
         if self.embed:
             super(Image,self).reload()
             if self.retina:
                 self._retina_shape()
 
     def _repr_html_(self):
         if not self.embed:
-            width = height = klass = ''
+            width = height = klass = alt = ''
             if self.width:
                 width = ' width="%d"' % self.width
             if self.height:
                 height = ' height="%d"' % self.height
             if self.unconfined:
                 klass = ' class="unconfined"'
-            return u'<img src="{url}"{width}{height}{klass}/>'.format(
+            if self.alt:
+                alt = ' alt="%s"' % html.escape(self.alt)
+            return u'<img src="{url}"{width}{height}{klass}{alt}/>'.format(
                 url=self.url,
                 width=width,
                 height=height,
                 klass=klass,
+                alt=alt,
             )
 
     def _repr_mimebundle_(self, include=None, exclude=None):
         """Return the image as a mimebundle
 
         Any new mimetype support should be implemented here.
         """
         if self.embed:
             mimetype = self._mimetype
             data, metadata = self._data_and_metadata(always_both=True)
             if metadata:
                 metadata = {mimetype: metadata}
             return {mimetype: data}, metadata
         else:
             return {'text/html': self._repr_html_()}
 
     def _data_and_metadata(self, always_both=False):
         """shortcut for returning metadata with shape information, if defined"""
         try:
             b64_data = b2a_base64(self.data).decode('ascii')
         except TypeError as e:
             raise FileNotFoundError(
                 "No such file or directory: '%s'" % (self.data)) from e
         md = {}
         if self.metadata:
             md.update(self.metadata)
         if self.width:
             md['width'] = self.width
         if self.height:
             md['height'] = self.height
         if self.unconfined:
             md['unconfined'] = self.unconfined
+        if self.alt:
+            md['alt'] = self.alt
         if md or always_both:
             return b64_data, md
         else:
             return b64_data
 
     def _repr_png_(self):
         if self.embed and self.format == self._FMT_PNG:
             return self._data_and_metadata()
 
     def _repr_jpeg_(self):
         if self.embed and self.format == self._FMT_JPEG:
             return self._data_and_metadata()
 
     def _find_ext(self, s):
         base, ext = splitext(s)
 
         if not ext:
             return base
 
         # `splitext` includes leading period, so we skip it
         return ext[1:].lower()
 
 
 class Video(DisplayObject):
 
     def __init__(self, data=None, url=None, filename=None, embed=False,
                  mimetype=None, width=None, height=None, html_attributes="controls"):
         """Create a video object given raw data or an URL.
 
         When this object is returned by an input cell or passed to the
         display function, it will result in the video being displayed
         in the frontend.
 
         Parameters
         ----------
         data : unicode, str or bytes
             The raw video data or a URL or filename to load the data from.
             Raw data will require passing ``embed=True``.
         url : unicode
             A URL for the video. If you specify ``url=``,
             the image data will not be embedded.
         filename : unicode
             Path to a local file containing the video.
             Will be interpreted as a local URL unless ``embed=True``.
         embed : bool
             Should the video be embedded using a data URI (True) or be
             loaded using a <video> tag (False).
 
             Since videos are large, embedding them should be avoided, if possible.
             You must confirm embedding as your intention by passing ``embed=True``.
 
             Local files can be displayed with URLs without embedding the content, via::
 
                 Video('./video.mp4')
         mimetype : unicode
             Specify the mimetype for embedded videos.
             Default will be guessed from file extension, if available.
         width : int
             Width in pixels to which to constrain the video in HTML.
             If not supplied, defaults to the width of the video.
         height : int
             Height in pixels to which to constrain the video in html.
             If not supplied, defaults to the height of the video.
         html_attributes : str
             Attributes for the HTML ``<video>`` block.
             Default: ``"controls"`` to get video controls.
             Other examples: ``"controls muted"`` for muted video with controls,
             ``"loop autoplay"`` for looping autoplaying video without controls.
 
         Examples
         --------
         ::
 
             Video('https://archive.org/download/Sita_Sings_the_Blues/Sita_Sings_the_Blues_small.mp4')
             Video('path/to/video.mp4')
             Video('path/to/video.mp4', embed=True)
             Video('path/to/video.mp4', embed=True, html_attributes="controls muted autoplay")
             Video(b'raw-videodata', embed=True)
         """
         if isinstance(data, (Path, PurePath)):
             data = str(data)
 
         if url is None and isinstance(data, str) and data.startswith(('http:', 'https:')):
             url = data
             data = None
         elif data is not None and os.path.exists(data):
             filename = data
             data = None
 
         if data and not embed:
             msg = ''.join([
                 "To embed videos, you must pass embed=True ",
                 "(this may make your notebook files huge)\n",
                 "Consider passing Video(url='...')",
             ])
             raise ValueError(msg)
 
         self.mimetype = mimetype
         self.embed = embed
         self.width = width
         self.height = height
         self.html_attributes = html_attributes
         super(Video, self).__init__(data=data, url=url, filename=filename)
 
     def _repr_html_(self):
         width = height = ''
         if self.width:
             width = ' width="%d"' % self.width
         if self.height:
             height = ' height="%d"' % self.height
 
         # External URLs and potentially local files are not embedded into the
         # notebook output.
         if not self.embed:
             url = self.url if self.url is not None else self.filename
             output = """<video src="{0}" {1} {2} {3}>
       Your browser does not support the <code>video</code> element.
     </video>""".format(url, self.html_attributes, width, height)
             return output
 
         # Embedded videos are base64-encoded.
         mimetype = self.mimetype
         if self.filename is not None:
             if not mimetype:
                 mimetype, _ = mimetypes.guess_type(self.filename)
 
             with open(self.filename, 'rb') as f:
                 video = f.read()
         else:
             video = self.data
         if isinstance(video, str):
             # unicode input is already b64-encoded
             b64_video = video
         else:
             b64_video = b2a_base64(video).decode('ascii').rstrip()
 
         output = """<video {0} {1} {2}>
  <source src="data:{3};base64,{4}" type="{3}">
  Your browser does not support the video tag.
  </video>""".format(self.html_attributes, width, height, mimetype, b64_video)
         return output
 
     def reload(self):
         # TODO
         pass
 
 
 @skip_doctest
 def set_matplotlib_formats(*formats, **kwargs):
     """Select figure formats for the inline backend. Optionally pass quality for JPEG.
 
     For example, this enables PNG and JPEG output with a JPEG quality of 90%::
 
         In [1]: set_matplotlib_formats('png', 'jpeg', quality=90)
 
     To set this in your config files use the following::
 
         c.InlineBackend.figure_formats = {'png', 'jpeg'}
         c.InlineBackend.print_figure_kwargs.update({'quality' : 90})
 
     Parameters
     ----------
     *formats : strs
         One or more figure formats to enable: 'png', 'retina', 'jpeg', 'svg', 'pdf'.
     **kwargs
         Keyword args will be relayed to ``figure.canvas.print_figure``.
     """
     from IPython.core.interactiveshell import InteractiveShell
     from IPython.core.pylabtools import select_figure_formats
     # build kwargs, starting with InlineBackend config
     kw = {}
     from ipykernel.pylab.config import InlineBackend
     cfg = InlineBackend.instance()
     kw.update(cfg.print_figure_kwargs)
     kw.update(**kwargs)
     shell = InteractiveShell.instance()
     select_figure_formats(shell, formats, **kw)
 
 @skip_doctest
 def set_matplotlib_close(close=True):
     """Set whether the inline backend closes all figures automatically or not.
 
     By default, the inline backend used in the IPython Notebook will close all
     matplotlib figures automatically after each cell is run. This means that
     plots in different cells won't interfere. Sometimes, you may want to make
     a plot in one cell and then refine it in later cells. This can be accomplished
     by::
 
         In [1]: set_matplotlib_close(False)
 
     To set this in your config files use the following::
 
         c.InlineBackend.close_figures = False
 
     Parameters
     ----------
     close : bool
         Should all matplotlib figures be automatically closed after each cell is
         run?
     """
     from ipykernel.pylab.config import InlineBackend
     cfg = InlineBackend.instance()
     cfg.close_figures = close

IPython/core/tests/test_display.py

@@ -1,459 +1,477 b''
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
 import json
 import os
 import warnings
 
 from unittest import mock
 
 import nose.tools as nt
 
 from IPython import display
 from IPython.core.getipython import get_ipython
 from IPython.utils.io import capture_output
 from IPython.utils.tempdir import NamedFileInTemporaryDirectory
 from IPython import paths as ipath
 from IPython.testing.tools import AssertNotPrints
 
 import IPython.testing.decorators as dec
 
 def test_image_size():
     """Simple test for display.Image(args, width=x,height=y)"""
     thisurl = 'http://www.google.fr/images/srpr/logo3w.png'
     img = display.Image(url=thisurl, width=200, height=200)
     nt.assert_equal(u'<img src="%s" width="200" height="200"/>' % (thisurl), img._repr_html_())
     img = display.Image(url=thisurl, metadata={'width':200, 'height':200})
     nt.assert_equal(u'<img src="%s" width="200" height="200"/>' % (thisurl), img._repr_html_())
     img = display.Image(url=thisurl, width=200)
     nt.assert_equal(u'<img src="%s" width="200"/>' % (thisurl), img._repr_html_())
     img = display.Image(url=thisurl)
     nt.assert_equal(u'<img src="%s"/>' % (thisurl), img._repr_html_())
     img = display.Image(url=thisurl, unconfined=True)
     nt.assert_equal(u'<img src="%s" class="unconfined"/>' % (thisurl), img._repr_html_())
 
 
 def test_image_mimes():
     fmt = get_ipython().display_formatter.format
     for format in display.Image._ACCEPTABLE_EMBEDDINGS:
         mime = display.Image._MIMETYPES[format]
         img = display.Image(b'garbage', format=format)
         data, metadata = fmt(img)
         nt.assert_equal(sorted(data), sorted([mime, 'text/plain']))
 
 
 def test_geojson():
 
     gj = display.GeoJSON(data={
             "type": "Feature",
             "geometry": {
                 "type": "Point",
                 "coordinates": [-81.327, 296.038]
             },
             "properties": {
                 "name": "Inca City"
             }
         },
         url_template="http://s3-eu-west-1.amazonaws.com/whereonmars.cartodb.net/{basemap_id}/{z}/{x}/{y}.png",
         layer_options={
             "basemap_id": "celestia_mars-shaded-16k_global",
             "attribution": "Celestia/praesepe",
             "minZoom": 0,
             "maxZoom": 18,
         })
     nt.assert_equal(u'<IPython.core.display.GeoJSON object>', str(gj))
 
 def test_retina_png():
     here = os.path.dirname(__file__)
     img = display.Image(os.path.join(here, "2x2.png"), retina=True)
     nt.assert_equal(img.height, 1)
     nt.assert_equal(img.width, 1)
     data, md = img._repr_png_()
     nt.assert_equal(md['width'], 1)
     nt.assert_equal(md['height'], 1)
 
 def test_embed_svg_url():
     import gzip
     from io import BytesIO
     svg_data = b'<svg><circle x="0" y="0" r="1"/></svg>'
     url = 'http://test.com/circle.svg'
     
     gzip_svg = BytesIO()
     with gzip.open(gzip_svg, 'wb') as fp:
         fp.write(svg_data)
     gzip_svg = gzip_svg.getvalue()
     
     def mocked_urlopen(*args, **kwargs):
         class MockResponse:
             def __init__(self, svg):
                 self._svg_data = svg
                 self.headers = {'content-type': 'image/svg+xml'}
 
             def read(self):
                 return self._svg_data
 
         if args[0] == url:
             return MockResponse(svg_data)
         elif args[0] == url + 'z':          
             ret= MockResponse(gzip_svg)
             ret.headers['content-encoding']= 'gzip'
             return ret
         return MockResponse(None)
 
     with mock.patch('urllib.request.urlopen', side_effect=mocked_urlopen):
         svg = display.SVG(url=url)
         nt.assert_true(svg._repr_svg_().startswith('<svg'))
         svg = display.SVG(url=url + 'z')
         nt.assert_true(svg._repr_svg_().startswith('<svg'))
     
 def test_retina_jpeg():
     here = os.path.dirname(__file__)
     img = display.Image(os.path.join(here, "2x2.jpg"), retina=True)
     nt.assert_equal(img.height, 1)
     nt.assert_equal(img.width, 1)
     data, md = img._repr_jpeg_()
     nt.assert_equal(md['width'], 1)
     nt.assert_equal(md['height'], 1)
 
 def test_base64image():
     display.Image("iVBORw0KGgoAAAANSUhEUgAAAAEAAAABAQMAAAAl21bKAAAAA1BMVEUAAACnej3aAAAAAWJLR0QAiAUdSAAAAAlwSFlzAAALEwAACxMBAJqcGAAAAAd0SU1FB94BCRQnOqNu0b4AAAAKSURBVAjXY2AAAAACAAHiIbwzAAAAAElFTkSuQmCC")
 
 def test_image_filename_defaults():
     '''test format constraint, and validity of jpeg and png'''
     tpath = ipath.get_ipython_package_dir()
     nt.assert_raises(ValueError, display.Image, filename=os.path.join(tpath, 'testing/tests/badformat.zip'),
                      embed=True)
     nt.assert_raises(ValueError, display.Image)
     nt.assert_raises(ValueError, display.Image, data='this is not an image', format='badformat', embed=True)
     # check boths paths to allow packages to test at build and install time
     imgfile = os.path.join(tpath, 'core/tests/2x2.png')
     img = display.Image(filename=imgfile)
     nt.assert_equal('png', img.format)
     nt.assert_is_not_none(img._repr_png_())
     img = display.Image(filename=os.path.join(tpath, 'testing/tests/logo.jpg'), embed=False)
     nt.assert_equal('jpeg', img.format)
     nt.assert_is_none(img._repr_jpeg_())
 
 def _get_inline_config():
     from ipykernel.pylab.config import InlineBackend
     return InlineBackend.instance()
 
 
 @dec.skip_without("ipykernel")
 @dec.skip_without("matplotlib")
 def test_set_matplotlib_close():
     cfg = _get_inline_config()
     cfg.close_figures = False
     display.set_matplotlib_close()
     assert cfg.close_figures
     display.set_matplotlib_close(False)
     assert not cfg.close_figures
 
 _fmt_mime_map = {
     'png': 'image/png',
     'jpeg': 'image/jpeg',
     'pdf': 'application/pdf',
     'retina': 'image/png',
     'svg': 'image/svg+xml',
 }
 
 @dec.skip_without('matplotlib')
 def test_set_matplotlib_formats():
     from matplotlib.figure import Figure
     formatters = get_ipython().display_formatter.formatters
     for formats in [
         ('png',),
         ('pdf', 'svg'),
         ('jpeg', 'retina', 'png'),
         (),
     ]:
         active_mimes = {_fmt_mime_map[fmt] for fmt in formats}
         display.set_matplotlib_formats(*formats)
         for mime, f in formatters.items():
             if mime in active_mimes:
                 nt.assert_in(Figure, f)
             else:
                 nt.assert_not_in(Figure, f)
 
 
 @dec.skip_without("ipykernel")
 @dec.skip_without("matplotlib")
 def test_set_matplotlib_formats_kwargs():
     from matplotlib.figure import Figure
     ip = get_ipython()
     cfg = _get_inline_config()
     cfg.print_figure_kwargs.update(dict(foo='bar'))
     kwargs = dict(quality=10)
     display.set_matplotlib_formats('png', **kwargs)
     formatter = ip.display_formatter.formatters['image/png']
     f = formatter.lookup_by_type(Figure)
     cell = f.__closure__[0].cell_contents
     expected = kwargs
     expected.update(cfg.print_figure_kwargs)
     nt.assert_equal(cell, expected)
 
 def test_display_available():
     """
     Test that display is available without import
 
     We don't really care if it's in builtin or anything else, but it should
     always be available.
     """
     ip = get_ipython()
     with AssertNotPrints('NameError'):
         ip.run_cell('display')
     try:
         ip.run_cell('del display')
     except NameError:
         pass # it's ok, it might be in builtins
     # even if deleted it should be back
     with AssertNotPrints('NameError'):
         ip.run_cell('display')
 
 def test_textdisplayobj_pretty_repr():
      p = display.Pretty("This is a simple test")
      nt.assert_equal(repr(p), '<IPython.core.display.Pretty object>')
      nt.assert_equal(p.data, 'This is a simple test')
 
      p._show_mem_addr = True
      nt.assert_equal(repr(p), object.__repr__(p))
 
 def test_displayobject_repr():
     h = display.HTML('<br />')
     nt.assert_equal(repr(h), '<IPython.core.display.HTML object>')
     h._show_mem_addr = True
     nt.assert_equal(repr(h), object.__repr__(h))
     h._show_mem_addr = False
     nt.assert_equal(repr(h), '<IPython.core.display.HTML object>')
 
     j = display.Javascript('')
     nt.assert_equal(repr(j), '<IPython.core.display.Javascript object>')
     j._show_mem_addr = True
     nt.assert_equal(repr(j), object.__repr__(j))
     j._show_mem_addr = False
     nt.assert_equal(repr(j), '<IPython.core.display.Javascript object>')
 
 @mock.patch('warnings.warn')
 def test_encourage_iframe_over_html(m_warn):
     display.HTML()
     m_warn.assert_not_called()
 
     display.HTML('<br />')
     m_warn.assert_not_called()
 
     display.HTML('<html><p>Lots of content here</p><iframe src="http://a.com"></iframe>')
     m_warn.assert_not_called()
 
     display.HTML('<iframe src="http://a.com"></iframe>')
     m_warn.assert_called_with('Consider using IPython.display.IFrame instead')
 
     m_warn.reset_mock()
     display.HTML('<IFRAME SRC="http://a.com"></IFRAME>')
     m_warn.assert_called_with('Consider using IPython.display.IFrame instead')
 
 def test_progress():
     p = display.ProgressBar(10)
     nt.assert_in('0/10',repr(p))
     p.html_width = '100%'
     p.progress = 5
     nt.assert_equal(p._repr_html_(), "<progress style='width:100%' max='10' value='5'></progress>")
 
 def test_progress_iter():
     with capture_output(display=False) as captured:
         for i in display.ProgressBar(5):
             out = captured.stdout
             nt.assert_in('{0}/5'.format(i), out)
     out = captured.stdout
     nt.assert_in('5/5', out)
 
 def test_json():
     d = {'a': 5}
     lis = [d]
     metadata = [
         {'expanded': False, 'root': 'root'},
         {'expanded': True,  'root': 'root'},
         {'expanded': False, 'root': 'custom'},
         {'expanded': True,  'root': 'custom'},
     ]
     json_objs = [
         display.JSON(d),
         display.JSON(d, expanded=True),
         display.JSON(d, root='custom'),
         display.JSON(d, expanded=True, root='custom'),
     ]
     for j, md in zip(json_objs, metadata):
         nt.assert_equal(j._repr_json_(), (d, md))
 
     with warnings.catch_warnings(record=True) as w:
         warnings.simplefilter("always")
         j = display.JSON(json.dumps(d))
         nt.assert_equal(len(w), 1)
         nt.assert_equal(j._repr_json_(), (d, metadata[0]))
 
     json_objs = [
         display.JSON(lis),
         display.JSON(lis, expanded=True),
         display.JSON(lis, root='custom'),
         display.JSON(lis, expanded=True, root='custom'),
     ]
     for j, md in zip(json_objs, metadata):
         nt.assert_equal(j._repr_json_(), (lis, md))
 
     with warnings.catch_warnings(record=True) as w:
         warnings.simplefilter("always")
         j = display.JSON(json.dumps(lis))
         nt.assert_equal(len(w), 1)
         nt.assert_equal(j._repr_json_(), (lis, metadata[0]))
 
 def test_video_embedding():
     """use a tempfile, with dummy-data, to ensure that video embedding doesn't crash"""
     v = display.Video("http://ignored")
     assert not v.embed
     html = v._repr_html_()
     nt.assert_not_in('src="data:', html)
     nt.assert_in('src="http://ignored"', html)
 
     with nt.assert_raises(ValueError):
         v = display.Video(b'abc')
 
     with NamedFileInTemporaryDirectory('test.mp4') as f:
         f.write(b'abc')
         f.close()
 
         v = display.Video(f.name)
         assert not v.embed
         html = v._repr_html_()
         nt.assert_not_in('src="data:', html)
 
         v = display.Video(f.name, embed=True)
         html = v._repr_html_()
         nt.assert_in('src="data:video/mp4;base64,YWJj"',html)
 
         v = display.Video(f.name, embed=True, mimetype='video/other')
         html = v._repr_html_()
         nt.assert_in('src="data:video/other;base64,YWJj"',html)
 
         v = display.Video(b'abc', embed=True, mimetype='video/mp4')
         html = v._repr_html_()
         nt.assert_in('src="data:video/mp4;base64,YWJj"',html)
 
         v = display.Video(u'YWJj', embed=True, mimetype='video/xyz')
         html = v._repr_html_()
         nt.assert_in('src="data:video/xyz;base64,YWJj"',html)
 
 def test_html_metadata():
     s = "<h1>Test</h1>"
     h = display.HTML(s, metadata={"isolated": True})
     nt.assert_equal(h._repr_html_(), (s, {"isolated": True}))
 
 def test_display_id():
     ip = get_ipython()
     with mock.patch.object(ip.display_pub, 'publish') as pub:
         handle = display.display('x')
         nt.assert_is(handle, None)
         handle = display.display('y', display_id='secret')
         nt.assert_is_instance(handle, display.DisplayHandle)
         handle2 = display.display('z', display_id=True)
         nt.assert_is_instance(handle2, display.DisplayHandle)
     nt.assert_not_equal(handle.display_id, handle2.display_id)
 
     nt.assert_equal(pub.call_count, 3)
     args, kwargs = pub.call_args_list[0]
     nt.assert_equal(args, ())
     nt.assert_equal(kwargs, {
         'data': {
             'text/plain': repr('x')
         },
         'metadata': {},
     })
     args, kwargs = pub.call_args_list[1]
     nt.assert_equal(args, ())
     nt.assert_equal(kwargs, {
         'data': {
             'text/plain': repr('y')
         },
         'metadata': {},
         'transient': {
             'display_id': handle.display_id,
         },
     })
     args, kwargs = pub.call_args_list[2]
     nt.assert_equal(args, ())
     nt.assert_equal(kwargs, {
         'data': {
             'text/plain': repr('z')
         },
         'metadata': {},
         'transient': {
             'display_id': handle2.display_id,
         },
     })
 
 
 def test_update_display():
     ip = get_ipython()
     with mock.patch.object(ip.display_pub, 'publish') as pub:
         with nt.assert_raises(TypeError):
             display.update_display('x')
         display.update_display('x', display_id='1')
         display.update_display('y', display_id='2')
     args, kwargs = pub.call_args_list[0]
     nt.assert_equal(args, ())
     nt.assert_equal(kwargs, {
         'data': {
             'text/plain': repr('x')
         },
         'metadata': {},
         'transient': {
             'display_id': '1',
         },
         'update': True,
     })
     args, kwargs = pub.call_args_list[1]
     nt.assert_equal(args, ())
     nt.assert_equal(kwargs, {
         'data': {
             'text/plain': repr('y')
         },
         'metadata': {},
         'transient': {
             'display_id': '2',
         },
         'update': True,
     })
 
 
 def test_display_handle():
     ip = get_ipython()
     handle = display.DisplayHandle()
     nt.assert_is_instance(handle.display_id, str)
     handle = display.DisplayHandle('my-id')
     nt.assert_equal(handle.display_id, 'my-id')
     with mock.patch.object(ip.display_pub, 'publish') as pub:
         handle.display('x')
         handle.update('y')
 
     args, kwargs = pub.call_args_list[0]
     nt.assert_equal(args, ())
     nt.assert_equal(kwargs, {
         'data': {
             'text/plain': repr('x')
         },
         'metadata': {},
         'transient': {
             'display_id': handle.display_id,
         }
     })
     args, kwargs = pub.call_args_list[1]
     nt.assert_equal(args, ())
     nt.assert_equal(kwargs, {
         'data': {
             'text/plain': repr('y')
         },
         'metadata': {},
         'transient': {
             'display_id': handle.display_id,
         },
         'update': True,
     })
 
+def test_image_alt_tag():
+    """Simple test for display.Image(args, alt=x,)"""
+    thisurl = 'http://example.com/image.png'
+    img = display.Image(url=thisurl, alt='an image')
+    nt.assert_equal(u'<img src="%s" alt="an image"/>' % (thisurl), img._repr_html_())
+    img = display.Image(url=thisurl, unconfined=True, alt='an image')
+    nt.assert_equal(u'<img src="%s" class="unconfined" alt="an image"/>' % (thisurl), img._repr_html_())
+    img = display.Image(url=thisurl, alt='>"& <')
+    nt.assert_equal(u'<img src="%s" alt="&gt;&quot;&amp; &lt;"/>' % (thisurl), img._repr_html_())
+
+    img = display.Image(url=thisurl, metadata={'alt':'an image'})
+    nt.assert_equal(img.alt, 'an image')
+
+    here = os.path.dirname(__file__)
+    img = display.Image(os.path.join(here, "2x2.png"), alt='an image')
+    nt.assert_equal(img.alt, 'an image')
+    _, md = img._repr_png_()
+    nt.assert_equal(md['alt'], 'an image')