IPython/core/displayhook.py

# -*- coding: utf-8 -*-
"""Displayhook for IPython.

This defines a callable class that IPython uses for `sys.displayhook`.
"""

# Copyright (c) IPython Development Team.
# Distributed under the terms of the Modified BSD License.

from __future__ import print_function

import sys
import io as _io
import tokenize

from traitlets.config.configurable import Configurable
from IPython.utils.py3compat import builtin_mod, cast_unicode_py2
from traitlets import Instance, Float
from warnings import warn

# TODO: Move the various attributes (cache_size, [others now moved]). Some
# of these are also attributes of InteractiveShell. They should be on ONE object
# only and the other objects should ask that one object for their values.

class DisplayHook(Configurable):
    """The custom IPython displayhook to replace sys.displayhook.

    This class does many things, but the basic idea is that it is a callable
    that gets called anytime user code returns a value.
    """

    shell = Instance('IPython.core.interactiveshell.InteractiveShellABC',
                     allow_none=True)
    exec_result = Instance('IPython.core.interactiveshell.ExecutionResult',
                           allow_none=True)
    cull_fraction = Float(0.2)

    def __init__(self, shell=None, cache_size=1000, **kwargs):
        super(DisplayHook, self).__init__(shell=shell, **kwargs)
        cache_size_min = 3
        if cache_size <= 0:
            self.do_full_cache = 0
            cache_size = 0
        elif cache_size < cache_size_min:
            self.do_full_cache = 0
            cache_size = 0
            warn('caching was disabled (min value for cache size is %s).' %
                 cache_size_min,level=3)
        else:
            self.do_full_cache = 1

        self.cache_size = cache_size

        # we need a reference to the user-level namespace
        self.shell = shell
        
        self._,self.__,self.___ = '','',''

        # these are deliberately global:
        to_user_ns = {'_':self._,'__':self.__,'___':self.___}
        self.shell.user_ns.update(to_user_ns)

    @property
    def prompt_count(self):
        return self.shell.execution_count

    #-------------------------------------------------------------------------
    # Methods used in __call__. Override these methods to modify the behavior
    # of the displayhook.
    #-------------------------------------------------------------------------

    def check_for_underscore(self):
        """Check if the user has set the '_' variable by hand."""
        # If something injected a '_' variable in __builtin__, delete
        # ipython's automatic one so we don't clobber that.  gettext() in
        # particular uses _, so we need to stay away from it.
        if '_' in builtin_mod.__dict__:
            try:
                del self.shell.user_ns['_']
            except KeyError:
                pass

    def quiet(self):
        """Should we silence the display hook because of ';'?"""
        # do not print output if input ends in ';'
        
        try:
            cell = cast_unicode_py2(self.shell.history_manager.input_hist_parsed[-1])
        except IndexError:
            # some uses of ipshellembed may fail here
            return False
        
        sio = _io.StringIO(cell)
        tokens = list(tokenize.generate_tokens(sio.readline))

        for token in reversed(tokens):
            if token[0] in (tokenize.ENDMARKER, tokenize.NL, tokenize.NEWLINE, tokenize.COMMENT):
                continue
            if (token[0] == tokenize.OP) and (token[1] == ';'):
                return True
            else:
                return False

    def start_displayhook(self):
        """Start the displayhook, initializing resources."""
        pass

    def write_output_prompt(self):
        """Write the output prompt.

        The default implementation simply writes the prompt to
        ``io.stdout``.
        """
        # Use write, not print which adds an extra space.
        sys.stdout.write(self.shell.separate_out)
        outprompt = 'Out[{}]: '.format(self.shell.execution_count)
        if self.do_full_cache:
            sys.stdout.write(outprompt)

    def compute_format_data(self, result):
        """Compute format data of the object to be displayed.

        The format data is a generalization of the :func:`repr` of an object.
        In the default implementation the format data is a :class:`dict` of
        key value pair where the keys are valid MIME types and the values
        are JSON'able data structure containing the raw data for that MIME
        type. It is up to frontends to determine pick a MIME to to use and
        display that data in an appropriate manner.

        This method only computes the format data for the object and should
        NOT actually print or write that to a stream.

        Parameters
        ----------
        result : object
            The Python object passed to the display hook, whose format will be
            computed.

        Returns
        -------
        (format_dict, md_dict) : dict
            format_dict is a :class:`dict` whose keys are valid MIME types and values are
            JSON'able raw data for that MIME type. It is recommended that
            all return values of this should always include the "text/plain"
            MIME type representation of the object.
            md_dict is a :class:`dict` with the same MIME type keys
            of metadata associated with each output.
            
        """
        return self.shell.display_formatter.format(result)

    # This can be set to True by the write_output_prompt method in a subclass
    prompt_end_newline = False

    def write_format_data(self, format_dict, md_dict=None):
        """Write the format data dict to the frontend.

        This default version of this method simply writes the plain text
        representation of the object to ``io.stdout``. Subclasses should
        override this method to send the entire `format_dict` to the
        frontends.

        Parameters
        ----------
        format_dict : dict
            The format dict for the object passed to `sys.displayhook`.
        md_dict : dict (optional)
            The metadata dict to be associated with the display data.
        """
        if 'text/plain' not in format_dict:
            # nothing to do
            return
        # We want to print because we want to always make sure we have a
        # newline, even if all the prompt separators are ''. This is the
        # standard IPython behavior.
        result_repr = format_dict['text/plain']
        if '\n' in result_repr:
            # So that multi-line strings line up with the left column of
            # the screen, instead of having the output prompt mess up
            # their first line.
            # We use the prompt template instead of the expanded prompt
            # because the expansion may add ANSI escapes that will interfere
            # with our ability to determine whether or not we should add
            # a newline.
            if not self.prompt_end_newline:
                # But avoid extraneous empty lines.
                result_repr = '\n' + result_repr

        print(result_repr)

    def update_user_ns(self, result):
        """Update user_ns with various things like _, __, _1, etc."""

        # Avoid recursive reference when displaying _oh/Out
        if result is not self.shell.user_ns['_oh']:
            if len(self.shell.user_ns['_oh']) >= self.cache_size and self.do_full_cache:
                self.cull_cache()
            # Don't overwrite '_' and friends if '_' is in __builtin__ (otherwise
            # we cause buggy behavior for things like gettext).

            if '_' not in builtin_mod.__dict__:
                self.___ = self.__
                self.__ = self._
                self._ = result
                self.shell.push({'_':self._,
                                 '__':self.__,
                                '___':self.___}, interactive=False)

            # hackish access to top-level  namespace to create _1,_2... dynamically
            to_main = {}
            if self.do_full_cache:
                new_result = '_'+repr(self.prompt_count)
                to_main[new_result] = result
                self.shell.push(to_main, interactive=False)
                self.shell.user_ns['_oh'][self.prompt_count] = result

    def fill_exec_result(self, result):
        if self.exec_result is not None:
            self.exec_result.result = result

    def log_output(self, format_dict):
        """Log the output."""
        if 'text/plain' not in format_dict:
            # nothing to do
            return
        if self.shell.logger.log_output:
            self.shell.logger.log_write(format_dict['text/plain'], 'output')
        self.shell.history_manager.output_hist_reprs[self.prompt_count] = \
                                                    format_dict['text/plain']

    def finish_displayhook(self):
        """Finish up all displayhook activities."""
        sys.stdout.write(self.shell.separate_out2)
        sys.stdout.flush()

    def __call__(self, result=None):
        """Printing with history cache management.

        This is invoked everytime the interpreter needs to print, and is
        activated by setting the variable sys.displayhook to it.
        """
        self.check_for_underscore()
        if result is not None and not self.quiet():
            self.start_displayhook()
            self.write_output_prompt()
            format_dict, md_dict = self.compute_format_data(result)
            self.update_user_ns(result)
            self.fill_exec_result(result)
            if format_dict:
                self.write_format_data(format_dict, md_dict)
                self.log_output(format_dict)
            self.finish_displayhook()

    def cull_cache(self):
        """Output cache is full, cull the oldest entries"""
        oh = self.shell.user_ns.get('_oh', {})
        sz = len(oh)
        cull_count = max(int(sz * self.cull_fraction), 2)
        warn('Output cache limit (currently {sz} entries) hit.\n'
             'Flushing oldest {cull_count} entries.'.format(sz=sz, cull_count=cull_count))
        
        for i, n in enumerate(sorted(oh)):
            if i >= cull_count:
                break
            self.shell.user_ns.pop('_%i' % n, None)
            oh.pop(n, None)
        

    def flush(self):
        if not self.do_full_cache:
            raise ValueError("You shouldn't have reached the cache flush "
                             "if full caching is not enabled!")
        # delete auto-generated vars from global namespace

        for n in range(1,self.prompt_count + 1):
            key = '_'+repr(n)
            try:
                del self.shell.user_ns[key]
            except: pass
        # In some embedded circumstances, the user_ns doesn't have the
        # '_oh' key set up.
        oh = self.shell.user_ns.get('_oh', None)
        if oh is not None:
            oh.clear()

        # Release our own references to objects:
        self._, self.__, self.___ = '', '', ''

        if '_' not in builtin_mod.__dict__:
            self.shell.user_ns.update({'_':None,'__':None, '___':None})
        import gc
        # TODO: Is this really needed?
        # IronPython blocks here forever
        if sys.platform != "cli":
            gc.collect()