Documentation update

IPython/core/magic.py

@@ -1,757 +1,757 b''
 # encoding: utf-8
 """Magic functions for InteractiveShell.
 """
 
 #-----------------------------------------------------------------------------
 #  Copyright (C) 2001 Janko Hauser <[e-mail]> and
 #  Copyright (C) 2001 Fernando Perez <[e-mail]>
 #  Copyright (C) 2008 The IPython Development Team
 
 #  Distributed under the terms of the BSD License.  The full license is in
 #  the file COPYING, distributed as part of this software.
 #-----------------------------------------------------------------------------
 
 import os
 import re
 import sys
 from getopt import getopt, GetoptError
 
 from traitlets.config.configurable import Configurable
 from . import oinspect
 from .error import UsageError
 from .inputtransformer2 import ESC_MAGIC, ESC_MAGIC2
 from ..utils.ipstruct import Struct
 from ..utils.process import arg_split
 from ..utils.text import dedent
 from traitlets import Bool, Dict, Instance, observe
 from logging import error
 
 #-----------------------------------------------------------------------------
 # Globals
 #-----------------------------------------------------------------------------
 
 # A dict we'll use for each class that has magics, used as temporary storage to
 # pass information between the @line/cell_magic method decorators and the
 # @magics_class class decorator, because the method decorators have no
 # access to the class when they run.  See for more details:
 # http://stackoverflow.com/questions/2366713/can-a-python-decorator-of-an-instance-method-access-the-class
 
 magics = dict(line={}, cell={})
 
 magic_kinds = ('line', 'cell')
 magic_spec = ('line', 'cell', 'line_cell')
 magic_escapes = dict(line=ESC_MAGIC, cell=ESC_MAGIC2)
 
 #-----------------------------------------------------------------------------
 # Utility classes and functions
 #-----------------------------------------------------------------------------
 
 class Bunch: pass
 
 
 def on_off(tag):
     """Return an ON/OFF string for a 1/0 input. Simple utility function."""
     return ['OFF','ON'][tag]
 
 
 def compress_dhist(dh):
     """Compress a directory history into a new one with at most 20 entries.
 
     Return a new list made from the first and last 10 elements of dhist after
     removal of duplicates.
     """
     head, tail = dh[:-10], dh[-10:]
 
     newhead = []
     done = set()
     for h in head:
         if h in done:
             continue
         newhead.append(h)
         done.add(h)
 
     return newhead + tail
 
 
 def needs_local_scope(func):
     """Decorator to mark magic functions which need to local scope to run."""
     func.needs_local_scope = True
     return func
 
 #-----------------------------------------------------------------------------
 # Class and method decorators for registering magics
 #-----------------------------------------------------------------------------
 
 def magics_class(cls):
     """Class decorator for all subclasses of the main Magics class.
 
     Any class that subclasses Magics *must* also apply this decorator, to
     ensure that all the methods that have been decorated as line/cell magics
     get correctly registered in the class instance.  This is necessary because
     when method decorators run, the class does not exist yet, so they
     temporarily store their information into a module global.  Application of
     this class decorator copies that global data to the class instance and
     clears the global.
 
     Obviously, this mechanism is not thread-safe, which means that the
     *creation* of subclasses of Magic should only be done in a single-thread
     context.  Instantiation of the classes has no restrictions.  Given that
     these classes are typically created at IPython startup time and before user
     application code becomes active, in practice this should not pose any
     problems.
     """
     cls.registered = True
     cls.magics = dict(line = magics['line'],
                       cell = magics['cell'])
     magics['line'] = {}
     magics['cell'] = {}
     return cls
 
 
 def record_magic(dct, magic_kind, magic_name, func):
     """Utility function to store a function as a magic of a specific kind.
 
     Parameters
     ----------
     dct : dict
         A dictionary with 'line' and 'cell' subdicts.
     magic_kind : str
         Kind of magic to be stored.
     magic_name : str
         Key to store the magic as.
     func : function
         Callable object to store.
     """
     if magic_kind == 'line_cell':
         dct['line'][magic_name] = dct['cell'][magic_name] = func
     else:
         dct[magic_kind][magic_name] = func
 
 
 def validate_type(magic_kind):
     """Ensure that the given magic_kind is valid.
 
     Check that the given magic_kind is one of the accepted spec types (stored
     in the global `magic_spec`), raise ValueError otherwise.
     """
     if magic_kind not in magic_spec:
         raise ValueError('magic_kind must be one of %s, %s given' %
                          magic_kinds, magic_kind)
 
 
 # The docstrings for the decorator below will be fairly similar for the two
 # types (method and function), so we generate them here once and reuse the
 # templates below.
 _docstring_template = \
 """Decorate the given {0} as {1} magic.
 
 The decorator can be used with or without arguments, as follows.
 
 i) without arguments: it will create a {1} magic named as the {0} being
 decorated::
 
     @deco
     def foo(...)
 
 will create a {1} magic named `foo`.
 
 ii) with one string argument: which will be used as the actual name of the
 resulting magic::
 
     @deco('bar')
     def foo(...)
 
 will create a {1} magic named `bar`.
 
 To register a class magic use ``Interactiveshell.register_magic(class or instance)``.
 """
 
 # These two are decorator factories.  While they are conceptually very similar,
 # there are enough differences in the details that it's simpler to have them
 # written as completely standalone functions rather than trying to share code
 # and make a single one with convoluted logic.
 
 def _method_magic_marker(magic_kind):
     """Decorator factory for methods in Magics subclasses.
     """
 
     validate_type(magic_kind)
 
     # This is a closure to capture the magic_kind.  We could also use a class,
     # but it's overkill for just that one bit of state.
     def magic_deco(arg):
         if callable(arg):
             # "Naked" decorator call (just @foo, no args)
             func = arg
             name = func.__name__
             retval = arg
             record_magic(magics, magic_kind, name, name)
         elif isinstance(arg, str):
             # Decorator called with arguments (@foo('bar'))
             name = arg
             def mark(func, *a, **kw):
                 record_magic(magics, magic_kind, name, func.__name__)
                 return func
             retval = mark
         else:
             raise TypeError("Decorator can only be called with "
                             "string or function")
         return retval
 
     # Ensure the resulting decorator has a usable docstring
     magic_deco.__doc__ = _docstring_template.format('method', magic_kind)
     return magic_deco
 
 
 def _function_magic_marker(magic_kind):
     """Decorator factory for standalone functions.
     """
     validate_type(magic_kind)
     
     # This is a closure to capture the magic_kind.  We could also use a class,
     # but it's overkill for just that one bit of state.
     def magic_deco(arg):
         # Find get_ipython() in the caller's namespace
         caller = sys._getframe(1)
         for ns in ['f_locals', 'f_globals', 'f_builtins']:
             get_ipython = getattr(caller, ns).get('get_ipython')
             if get_ipython is not None:
                 break
         else:
             raise NameError('Decorator can only run in context where '
                             '`get_ipython` exists')
 
         ip = get_ipython()
 
         if callable(arg):
             # "Naked" decorator call (just @foo, no args)
             func = arg
             name = func.__name__
             ip.register_magic_function(func, magic_kind, name)
             retval = arg
         elif isinstance(arg, str):
             # Decorator called with arguments (@foo('bar'))
             name = arg
             def mark(func, *a, **kw):
                 ip.register_magic_function(func, magic_kind, name)
                 return func
             retval = mark
         else:
             raise TypeError("Decorator can only be called with "
                              "string or function")
         return retval
 
     # Ensure the resulting decorator has a usable docstring
     ds = _docstring_template.format('function', magic_kind)
 
     ds += dedent("""
     Note: this decorator can only be used in a context where IPython is already
     active, so that the `get_ipython()` call succeeds.  You can therefore use
     it in your startup files loaded after IPython initializes, but *not* in the
     IPython configuration file itself, which is executed before IPython is
     fully up and running.  Any file located in the `startup` subdirectory of
     your configuration profile will be OK in this sense.
     """)
     
     magic_deco.__doc__ = ds
     return magic_deco
 
 
 MAGIC_NO_VAR_EXPAND_ATTR = "_ipython_magic_no_var_expand"
 MAGIC_OUTPUT_CAN_BE_SILENCED = "_ipython_magic_output_can_be_silenced"
 
 
 def no_var_expand(magic_func):
     """Mark a magic function as not needing variable expansion
 
     By default, IPython interprets `{a}` or `$a` in the line passed to magics
     as variables that should be interpolated from the interactive namespace
     before passing the line to the magic function.
     This is not always desirable, e.g. when the magic executes Python code
     (%timeit, %time, etc.).
     Decorate magics with `@no_var_expand` to opt-out of variable expansion.
 
     .. versionadded:: 7.3
     """
     setattr(magic_func, MAGIC_NO_VAR_EXPAND_ATTR, True)
     return magic_func
 
 
 def output_can_be_silenced(magic_func):
     """Mark a magic function so its output may be silenced.
 
-    The output is silenced if the Python expression used as a parameter of
+    The output is silenced if the Python code used as a parameter of
     the magic ends in a semicolon, not counting a Python comment that can
     follow it.
     """
     setattr(magic_func, MAGIC_OUTPUT_CAN_BE_SILENCED, True)
     return magic_func
 
 # Create the actual decorators for public use
 
 # These three are used to decorate methods in class definitions
 line_magic = _method_magic_marker('line')
 cell_magic = _method_magic_marker('cell')
 line_cell_magic = _method_magic_marker('line_cell')
 
 # These three decorate standalone functions and perform the decoration
 # immediately.  They can only run where get_ipython() works
 register_line_magic = _function_magic_marker('line')
 register_cell_magic = _function_magic_marker('cell')
 register_line_cell_magic = _function_magic_marker('line_cell')
 
 #-----------------------------------------------------------------------------
 # Core Magic classes
 #-----------------------------------------------------------------------------
 
 class MagicsManager(Configurable):
     """Object that handles all magic-related functionality for IPython.
     """
     # Non-configurable class attributes
 
     # A two-level dict, first keyed by magic type, then by magic function, and
     # holding the actual callable object as value.  This is the dict used for
     # magic function dispatch
     magics = Dict()
     lazy_magics = Dict(
         help="""
     Mapping from magic names to modules to load.
 
     This can be used in IPython/IPykernel configuration to declare lazy magics
     that will only be imported/registered on first use.
 
     For example::
 
         c.MagicsManager.lazy_magics = {
           "my_magic": "slow.to.import",
           "my_other_magic": "also.slow",
         }
 
     On first invocation of `%my_magic`, `%%my_magic`, `%%my_other_magic` or
     `%%my_other_magic`, the corresponding module will be loaded as an ipython
     extensions as if you had previously done `%load_ext ipython`.
 
     Magics names should be without percent(s) as magics can be both cell
     and line magics.
 
     Lazy loading happen relatively late in execution process, and
     complex extensions that manipulate Python/IPython internal state or global state
     might not support lazy loading.
     """
     ).tag(
         config=True,
     )
 
     # A registry of the original objects that we've been given holding magics.
     registry = Dict()
 
     shell = Instance('IPython.core.interactiveshell.InteractiveShellABC', allow_none=True)
 
     auto_magic = Bool(True, help=
         "Automatically call line magics without requiring explicit % prefix"
     ).tag(config=True)
     @observe('auto_magic')
     def _auto_magic_changed(self, change):
         self.shell.automagic = change['new']
     
     _auto_status = [
         'Automagic is OFF, % prefix IS needed for line magics.',
         'Automagic is ON, % prefix IS NOT needed for line magics.']
 
     user_magics = Instance('IPython.core.magics.UserMagics', allow_none=True)
 
     def __init__(self, shell=None, config=None, user_magics=None, **traits):
 
         super(MagicsManager, self).__init__(shell=shell, config=config,
                                            user_magics=user_magics, **traits)
         self.magics = dict(line={}, cell={})
         # Let's add the user_magics to the registry for uniformity, so *all*
         # registered magic containers can be found there.
         self.registry[user_magics.__class__.__name__] = user_magics
 
     def auto_status(self):
         """Return descriptive string with automagic status."""
         return self._auto_status[self.auto_magic]
     
     def lsmagic(self):
         """Return a dict of currently available magic functions.
 
         The return dict has the keys 'line' and 'cell', corresponding to the
         two types of magics we support.  Each value is a list of names.
         """
         return self.magics
 
     def lsmagic_docs(self, brief=False, missing=''):
         """Return dict of documentation of magic functions.
 
         The return dict has the keys 'line' and 'cell', corresponding to the
         two types of magics we support. Each value is a dict keyed by magic
         name whose value is the function docstring. If a docstring is
         unavailable, the value of `missing` is used instead.
 
         If brief is True, only the first line of each docstring will be returned.
         """
         docs = {}
         for m_type in self.magics:
             m_docs = {}
             for m_name, m_func in self.magics[m_type].items():
                 if m_func.__doc__:
                     if brief:
                         m_docs[m_name] = m_func.__doc__.split('\n', 1)[0]
                     else:
                         m_docs[m_name] = m_func.__doc__.rstrip()
                 else:
                     m_docs[m_name] = missing
             docs[m_type] = m_docs
         return docs
 
     def register_lazy(self, name: str, fully_qualified_name: str):
         """
         Lazily register a magic via an extension.
 
 
         Parameters
         ----------
         name : str
             Name of the magic you wish to register.
         fully_qualified_name :
             Fully qualified name of the module/submodule that should be loaded
             as an extensions when the magic is first called.
             It is assumed that loading this extensions will register the given
             magic.
         """
 
         self.lazy_magics[name] = fully_qualified_name
 
     def register(self, *magic_objects):
         """Register one or more instances of Magics.
 
         Take one or more classes or instances of classes that subclass the main
         `core.Magic` class, and register them with IPython to use the magic
         functions they provide.  The registration process will then ensure that
         any methods that have decorated to provide line and/or cell magics will
         be recognized with the `%x`/`%%x` syntax as a line/cell magic
         respectively.
 
         If classes are given, they will be instantiated with the default
         constructor.  If your classes need a custom constructor, you should
         instanitate them first and pass the instance.
 
         The provided arguments can be an arbitrary mix of classes and instances.
 
         Parameters
         ----------
         *magic_objects : one or more classes or instances
         """
         # Start by validating them to ensure they have all had their magic
         # methods registered at the instance level
         for m in magic_objects:
             if not m.registered:
                 raise ValueError("Class of magics %r was constructed without "
                                  "the @register_magics class decorator")
             if isinstance(m, type):
                 # If we're given an uninstantiated class
                 m = m(shell=self.shell)
 
             # Now that we have an instance, we can register it and update the
             # table of callables
             self.registry[m.__class__.__name__] = m
             for mtype in magic_kinds:
                 self.magics[mtype].update(m.magics[mtype])
 
     def register_function(self, func, magic_kind='line', magic_name=None):
         """Expose a standalone function as magic function for IPython.
 
         This will create an IPython magic (line, cell or both) from a
         standalone function.  The functions should have the following
         signatures:
 
         * For line magics: `def f(line)`
         * For cell magics: `def f(line, cell)`
         * For a function that does both: `def f(line, cell=None)`
 
         In the latter case, the function will be called with `cell==None` when
         invoked as `%f`, and with cell as a string when invoked as `%%f`.
 
         Parameters
         ----------
         func : callable
             Function to be registered as a magic.
         magic_kind : str
             Kind of magic, one of 'line', 'cell' or 'line_cell'
         magic_name : optional str
             If given, the name the magic will have in the IPython namespace.  By
             default, the name of the function itself is used.
         """
 
         # Create the new method in the user_magics and register it in the
         # global table
         validate_type(magic_kind)
         magic_name = func.__name__ if magic_name is None else magic_name
         setattr(self.user_magics, magic_name, func)
         record_magic(self.magics, magic_kind, magic_name, func)
 
     def register_alias(self, alias_name, magic_name, magic_kind='line', magic_params=None):
         """Register an alias to a magic function.
 
         The alias is an instance of :class:`MagicAlias`, which holds the
         name and kind of the magic it should call. Binding is done at
         call time, so if the underlying magic function is changed the alias
         will call the new function.
 
         Parameters
         ----------
         alias_name : str
             The name of the magic to be registered.
         magic_name : str
             The name of an existing magic.
         magic_kind : str
             Kind of magic, one of 'line' or 'cell'
         """
 
         # `validate_type` is too permissive, as it allows 'line_cell'
         # which we do not handle.
         if magic_kind not in magic_kinds:
             raise ValueError('magic_kind must be one of %s, %s given' %
                              magic_kinds, magic_kind)
 
         alias = MagicAlias(self.shell, magic_name, magic_kind, magic_params)
         setattr(self.user_magics, alias_name, alias)
         record_magic(self.magics, magic_kind, alias_name, alias)
 
 # Key base class that provides the central functionality for magics.
 
 
 class Magics(Configurable):
     """Base class for implementing magic functions.
 
     Shell functions which can be reached as %function_name. All magic
     functions should accept a string, which they can parse for their own
     needs. This can make some functions easier to type, eg `%cd ../`
     vs. `%cd("../")`
 
     Classes providing magic functions need to subclass this class, and they
     MUST:
 
     - Use the method decorators `@line_magic` and `@cell_magic` to decorate
       individual methods as magic functions, AND
 
     - Use the class decorator `@magics_class` to ensure that the magic
       methods are properly registered at the instance level upon instance
       initialization.
 
     See :mod:`magic_functions` for examples of actual implementation classes.
     """
     # Dict holding all command-line options for each magic.
     options_table = None
     # Dict for the mapping of magic names to methods, set by class decorator
     magics = None
     # Flag to check that the class decorator was properly applied
     registered = False
     # Instance of IPython shell
     shell = None
 
     def __init__(self, shell=None, **kwargs):
         if not(self.__class__.registered):
             raise ValueError('Magics subclass without registration - '
                              'did you forget to apply @magics_class?')
         if shell is not None:
             if hasattr(shell, 'configurables'):
                 shell.configurables.append(self)
             if hasattr(shell, 'config'):
                 kwargs.setdefault('parent', shell)
 
         self.shell = shell
         self.options_table = {}
         # The method decorators are run when the instance doesn't exist yet, so
         # they can only record the names of the methods they are supposed to
         # grab.  Only now, that the instance exists, can we create the proper
         # mapping to bound methods.  So we read the info off the original names
         # table and replace each method name by the actual bound method.
         # But we mustn't clobber the *class* mapping, in case of multiple instances.
         class_magics = self.magics
         self.magics = {}
         for mtype in magic_kinds:
             tab = self.magics[mtype] = {}
             cls_tab = class_magics[mtype]
             for magic_name, meth_name in cls_tab.items():
                 if isinstance(meth_name, str):
                     # it's a method name, grab it
                     tab[magic_name] = getattr(self, meth_name)
                 else:
                     # it's the real thing
                     tab[magic_name] = meth_name
         # Configurable **needs** to be initiated at the end or the config
         # magics get screwed up.
         super(Magics, self).__init__(**kwargs)
 
     def arg_err(self,func):
         """Print docstring if incorrect arguments were passed"""
         print('Error in arguments:')
         print(oinspect.getdoc(func))
 
     def format_latex(self, strng):
         """Format a string for latex inclusion."""
 
         # Characters that need to be escaped for latex:
         escape_re = re.compile(r'(%|_|\$|#|&)',re.MULTILINE)
         # Magic command names as headers:
         cmd_name_re = re.compile(r'^(%s.*?):' % ESC_MAGIC,
                                  re.MULTILINE)
         # Magic commands
         cmd_re = re.compile(r'(?P<cmd>%s.+?\b)(?!\}\}:)' % ESC_MAGIC,
                             re.MULTILINE)
         # Paragraph continue
         par_re = re.compile(r'\\$',re.MULTILINE)
 
         # The "\n" symbol
         newline_re = re.compile(r'\\n')
 
         # Now build the string for output:
         #strng = cmd_name_re.sub(r'\n\\texttt{\\textsl{\\large \1}}:',strng)
         strng = cmd_name_re.sub(r'\n\\bigskip\n\\texttt{\\textbf{ \1}}:',
                                 strng)
         strng = cmd_re.sub(r'\\texttt{\g<cmd>}',strng)
         strng = par_re.sub(r'\\\\',strng)
         strng = escape_re.sub(r'\\\1',strng)
         strng = newline_re.sub(r'\\textbackslash{}n',strng)
         return strng
 
     def parse_options(self, arg_str, opt_str, *long_opts, **kw):
         """Parse options passed to an argument string.
 
         The interface is similar to that of :func:`getopt.getopt`, but it
         returns a :class:`~IPython.utils.struct.Struct` with the options as keys
         and the stripped argument string still as a string.
 
         arg_str is quoted as a true sys.argv vector by using shlex.split.
         This allows us to easily expand variables, glob files, quote
         arguments, etc.
 
         Parameters
         ----------
         arg_str : str
             The arguments to parse.
         opt_str : str
             The options specification.
         mode : str, default 'string'
             If given as 'list', the argument string is returned as a list (split
             on whitespace) instead of a string.
         list_all : bool, default False
             Put all option values in lists. Normally only options
             appearing more than once are put in a list.
         posix : bool, default True
             Whether to split the input line in POSIX mode or not, as per the
             conventions outlined in the :mod:`shlex` module from the standard
             library.
         """
 
         # inject default options at the beginning of the input line
         caller = sys._getframe(1).f_code.co_name
         arg_str = '%s %s' % (self.options_table.get(caller,''),arg_str)
 
         mode = kw.get('mode','string')
         if mode not in ['string','list']:
             raise ValueError('incorrect mode given: %s' % mode)
         # Get options
         list_all = kw.get('list_all',0)
         posix = kw.get('posix', os.name == 'posix')
         strict = kw.get('strict', True)
 
         preserve_non_opts = kw.get("preserve_non_opts", False)
         remainder_arg_str = arg_str
 
         # Check if we have more than one argument to warrant extra processing:
         odict = {}  # Dictionary with options
         args = arg_str.split()
         if len(args) >= 1:
             # If the list of inputs only has 0 or 1 thing in it, there's no
             # need to look for options
             argv = arg_split(arg_str, posix, strict)
             # Do regular option processing
             try:
                 opts,args = getopt(argv, opt_str, long_opts)
             except GetoptError as e:
                 raise UsageError(
                     '%s ( allowed: "%s" %s)' % (e.msg, opt_str, " ".join(long_opts))
                 ) from e
             for o, a in opts:
                 if mode == "string" and preserve_non_opts:
                     # remove option-parts from the original args-string and preserve remaining-part.
                     # This relies on the arg_split(...) and getopt(...)'s impl spec, that the parsed options are
                     # returned in the original order.
                     remainder_arg_str = remainder_arg_str.replace(o, "", 1).replace(
                         a, "", 1
                     )
                 if o.startswith("--"):
                     o = o[2:]
                 else:
                     o = o[1:]
                 try:
                     odict[o].append(a)
                 except AttributeError:
                     odict[o] = [odict[o],a]
                 except KeyError:
                     if list_all:
                         odict[o] = [a]
                     else:
                         odict[o] = a
 
         # Prepare opts,args for return
         opts = Struct(odict)
         if mode == 'string':
             if preserve_non_opts:
                 args = remainder_arg_str.lstrip()
             else:
                 args = " ".join(args)
 
         return opts,args
 
     def default_option(self, fn, optstr):
         """Make an entry in the options_table for fn, with value optstr"""
 
         if fn not in self.lsmagic():
             error("%s is not a magic function" % fn)
         self.options_table[fn] = optstr
 
 
 class MagicAlias(object):
     """An alias to another magic function.
 
     An alias is determined by its magic name and magic kind. Lookup
     is done at call time, so if the underlying magic changes the alias
     will call the new function.
 
     Use the :meth:`MagicsManager.register_alias` method or the
     `%alias_magic` magic function to create and register a new alias.
     """
     def __init__(self, shell, magic_name, magic_kind, magic_params=None):
         self.shell = shell
         self.magic_name = magic_name
         self.magic_params = magic_params
         self.magic_kind = magic_kind
 
         self.pretty_target = '%s%s' % (magic_escapes[self.magic_kind], self.magic_name)
         self.__doc__ = "Alias for `%s`." % self.pretty_target
 
         self._in_call = False
 
     def __call__(self, *args, **kwargs):
         """Call the magic alias."""
         fn = self.shell.find_magic(self.magic_name, self.magic_kind)
         if fn is None:
             raise UsageError("Magic `%s` not found." % self.pretty_target)
 
         # Protect against infinite recursion.
         if self._in_call:
             raise UsageError("Infinite recursion detected; "
                              "magic aliases cannot call themselves.")
         self._in_call = True
         try:
             if self.magic_params:
                 args_list = list(args)
                 args_list[0] = self.magic_params + " " + args[0]
                 args = tuple(args_list)
             return fn(*args, **kwargs)
         finally:
             self._in_call = False

docs/source/config/custommagics.rst

@@ -1,199 +1,212 b''
 .. _defining_magics:
 
 Defining custom magics
 ======================
 
 There are two main ways to define your own magic functions: from standalone
 functions and by inheriting from a base class provided by IPython:
 :class:`IPython.core.magic.Magics`. Below we show code you can place in a file
 that you load from your configuration, such as any file in the ``startup``
 subdirectory of your default IPython profile.
 
 First, let us see the simplest case. The following shows how to create a line
 magic, a cell one and one that works in both modes, using just plain functions:
 
 .. sourcecode:: python
 
     from IPython.core.magic import (register_line_magic, register_cell_magic,
                                     register_line_cell_magic)
 
     @register_line_magic
     def lmagic(line):
         "my line magic"
         return line
 
     @register_cell_magic
     def cmagic(line, cell):
         "my cell magic"
         return line, cell
 
     @register_line_cell_magic
     def lcmagic(line, cell=None):
         "Magic that works both as %lcmagic and as %%lcmagic"
         if cell is None:
             print("Called as line magic")
             return line
         else:
             print("Called as cell magic")
             return line, cell
 
     # In an interactive session, we need to delete these to avoid
     # name conflicts for automagic to work on line magics.
     del lmagic, lcmagic
 
 
 You can also create magics of all three kinds by inheriting from the
 :class:`IPython.core.magic.Magics` class.  This lets you create magics that can
 potentially hold state in between calls, and that have full access to the main
 IPython object:
     
 .. sourcecode:: python
 
     # This code can be put in any Python module, it does not require IPython
     # itself to be running already.  It only creates the magics subclass but
     # doesn't instantiate it yet.
     from __future__ import print_function
     from IPython.core.magic import (Magics, magics_class, line_magic,
                                     cell_magic, line_cell_magic)
 
     # The class MUST call this class decorator at creation time
     @magics_class
     class MyMagics(Magics):
 
         @line_magic
         def lmagic(self, line):
             "my line magic"
             print("Full access to the main IPython object:", self.shell)
             print("Variables in the user namespace:", list(self.shell.user_ns.keys()))
             return line
 
         @cell_magic
         def cmagic(self, line, cell):
             "my cell magic"
             return line, cell
 
         @line_cell_magic
         def lcmagic(self, line, cell=None):
             "Magic that works both as %lcmagic and as %%lcmagic"
             if cell is None:
                 print("Called as line magic")
                 return line
             else:
                 print("Called as cell magic")
                 return line, cell
 
 
     # In order to actually use these magics, you must register them with a
     # running IPython.
 
     def load_ipython_extension(ipython):
         """
         Any module file that define a function named `load_ipython_extension`
         can be loaded via `%load_ext module.path` or be configured to be
         autoloaded by IPython at startup time.
         """
         # You can register the class itself without instantiating it.  IPython will
         # call the default constructor on it.
         ipython.register_magics(MyMagics)
 
 If you want to create a class with a different constructor that holds
 additional state, then you should always call the parent constructor and
 instantiate the class yourself before registration:
 
 .. sourcecode:: python
 
     @magics_class
     class StatefulMagics(Magics):
         "Magics that hold additional state"
 
         def __init__(self, shell, data):
             # You must call the parent constructor
             super(StatefulMagics, self).__init__(shell)
             self.data = data
         
         # etc...
 
     def load_ipython_extension(ipython):
         """
         Any module file that define a function named `load_ipython_extension`
         can be loaded via `%load_ext module.path` or be configured to be
         autoloaded by IPython at startup time.
         """
         # This class must then be registered with a manually created instance,
         # since its constructor has different arguments from the default:
         magics = StatefulMagics(ipython, some_data)
         ipython.register_magics(magics)
 
 
 .. note::
 
    In early IPython versions 0.12 and before the line magics were
    created using a :func:`define_magic` API function.  This API has been
    replaced with the above in IPython 0.13 and then completely removed
    in IPython 5.  Maintainers of IPython extensions that still use the
    :func:`define_magic` function are advised to adjust their code
    for the current API.
 
 
 Accessing user namespace and local scope
 ========================================
 
 When creating line magics, you may need to access surrounding scope  to get user
-variables (e.g when called inside functions). IPython provide the
+variables (e.g when called inside functions). IPython provides the
 ``@needs_local_scope`` decorator that can be imported from
 ``IPython.core.magics``. When decorated with ``@needs_local_scope`` a magic will
 be passed ``local_ns`` as an argument. As a convenience ``@needs_local_scope``
 can also be applied to cell magics even if cell magics cannot appear at local
 scope context.
 
+Silencing the magic output
+==========================
+
+Sometimes it may be useful to define a magic that can be silenced the same way
+that non-magic expressions can, i.e., by appending a semicolon at the end of the Python
+code to be executed. That can be achieved by decorating the magic function with
+the decorator ``@output_can_be_silenced`` that can be imported from
+``IPython.core.magics``. When this decorator is used, IPython will parse the Python
+code used by the magic and, if the last token is a ``;``, the output created by the
+magic will not show up on the screen. If you want to see an example of this decorator
+in action, take a look on the ``time`` magic defined in
+``IPython.core.magics.execution.py``.
+
 Complete Example
 ================
 
 Here is a full example of a magic package. You can distribute magics using
 setuptools, distutils, or any other distribution tools like `flit
 <https://flit.readthedocs.io>`_ for pure Python packages.
 
 When distributing magics as part of a package, recommended best practice is to
 execute the registration inside the `load_ipython_extension` as demonstrated in
 the example below, instead of directly in the module (as in the initial example
 with the ``@register_*`` decorators). This means a user will need to explicitly
 choose to load your magic with ``%load_ext``. instead implicitly getting it when
 importing the module. This is particularly relevant if loading your magic has 
 side effects, if it is slow to load, or if it might override another magic with
 the same name. 
 
 .. sourcecode:: bash
 
    .
    ├── example_magic
    │   ├── __init__.py
    │   └── abracadabra.py
    └── setup.py
 
 .. sourcecode:: bash
 
    $ cat example_magic/__init__.py
    """An example magic"""
    __version__ = '0.0.1'
    
    from .abracadabra import Abracadabra
    
    def load_ipython_extension(ipython):
        ipython.register_magics(Abracadabra)
 
 .. sourcecode:: bash
 
     $ cat example_magic/abracadabra.py
     from IPython.core.magic import (Magics, magics_class, line_magic, cell_magic)
 
     @magics_class
     class Abracadabra(Magics):
 
         @line_magic
         def abra(self, line):
             return line
 
         @cell_magic
         def cadabra(self, line, cell):
             return line, cell