docs/source/interactive/reference.txt

=================
IPython reference
=================

.. _command_line_options:

Command-line usage
==================

You start IPython with the command::

    $ ipython [options] files

If invoked with no options, it executes all the files listed in sequence
and drops you into the interpreter while still acknowledging any options
you may have set in your ipython_config.py. This behavior is different from
standard Python, which when called as python -i will only execute one
file and ignore your configuration setup.

Please note that some of the configuration options are not available at
the command line, simply because they are not practical here. Look into
your configuration files for details on those. There are separate configuration 
files for each profile, and the files look like "ipython_config.py" or 
"ipython_config_<frontendname>.py".  Profile directories look like 
"profile_profilename" and are typically installed in the IPYTHON_DIR directory. 
For Linux users, this will be $HOME/.config/ipython, and for other users it 
will be $HOME/.ipython.  For Windows users, $HOME resolves to C:\\Documents and
Settings\\YourUserName in most instances.


Eventloop integration
---------------------

Previously IPython had command line options for controlling GUI event loop
integration (-gthread, -qthread, -q4thread, -wthread, -pylab). As of IPython
version 0.11, these have been removed. Please see the new ``%gui``
magic command or :ref:`this section <gui_support>` for details on the new
interface, or specify the gui at the commandline::

    $ ipython --gui=qt


Regular Options
---------------

After the above threading options have been given, regular options can
follow in any order. All options can be abbreviated to their shortest
non-ambiguous form and are case-sensitive. One or two dashes can be
used. Some options have an alternate short form, indicated after a ``|``.

Most options can also be set from your configuration file. See the provided
example for more details on what the options do. Options given at the command
line override the values set in the configuration file.

All options with a [no] prepended can be specified in negated form
(--no-option instead of --option) to turn the feature off.

    ``-h, --help``  print a help message and exit.

    ``--pylab, pylab=<name>``
    See :ref:`Matplotlib support <matplotlib_support>`
    for more details.

    ``--autocall=<val>``
	Make IPython automatically call any callable object even if you
	didn't type explicit parentheses. For example, 'str 43' becomes
	'str(43)' automatically. The value can be '0' to disable the feature,
	'1' for smart autocall, where it is not applied if there are no more
	arguments on the line, and '2' for full autocall, where all callable
	objects are automatically called (even if no arguments are
	present). The default is '1'.

    ``--[no-]autoindent``
	Turn automatic indentation on/off.

    ``--[no-]automagic``
	make magic commands automatic (without needing their first character
	to be %). Type %magic at the IPython prompt for more information.

    ``--[no-]autoedit_syntax``
	When a syntax error occurs after editing a file, automatically
	open the file to the trouble causing line for convenient
	fixing.

    ``--[no-]banner``
	Print the initial information banner (default on).

    ``-c <command>``
	execute the given command string. This is similar to the -c
	option in the normal Python interpreter.

    ``--cache-size=<n>``
	size of the output cache (maximum number of entries to hold in
	memory). The default is 1000, you can change it permanently in your
	config file. Setting it to 0 completely disables the caching system,
	and the minimum value accepted is 20 (if you provide a value less than
	20, it is reset to 0 and a warning is issued) This limit is defined
	because otherwise you'll spend more time re-flushing a too small cache
	than working.

    ``--classic``
	Gives IPython a similar feel to the classic Python
	prompt.

    ``--colors=<scheme>``
	Color scheme for prompts and exception reporting. Currently
	implemented: NoColor, Linux and LightBG.

    ``--[no-]color_info``
	IPython can display information about objects via a set of functions,
	and optionally can use colors for this, syntax highlighting source
	code and various other elements.  However, because this information is
	passed through a pager (like 'less') and many pagers get confused with
	color codes, this option is off by default. You can test it and turn
	it on permanently in your configuration file if it works for you. As a
	reference, the 'less' pager supplied with Mandrake 8.2 works ok, but
	that in RedHat 7.2 doesn't.

	Test it and turn it on permanently if it works with your
	system. The magic function %color_info allows you to toggle this
	interactively for testing.

    ``--[no-]debug``
	Show information about the loading process. Very useful to pin down
	problems with your configuration files or to get details about
	session restores.

    ``--[no-]deep_reload``
	IPython can use the deep_reload module which reloads changes in
	modules recursively (it replaces the reload() function, so you don't
	need to change anything to use it).  deep_reload() forces a full
	reload of modules whose code may have changed, which the default
	reload() function does not.

	When deep_reload is off, IPython will use the normal reload(),
	but deep_reload will still be available as dreload(). This
	feature is off by default [which means that you have both
	normal reload() and dreload()].

    ``--editor=<name>``
	Which editor to use with the %edit command. By default,
	IPython will honor your EDITOR environment variable (if not
	set, vi is the Unix default and notepad the Windows one).
	Since this editor is invoked on the fly by IPython and is
	meant for editing small code snippets, you may want to use a
	small, lightweight editor here (in case your default EDITOR is
	something like Emacs).

    ``--ipython_dir=<name>``
	name of your IPython configuration directory IPYTHON_DIR. This
	can also be specified through the environment variable
	IPYTHON_DIR.

    ``--logfile=<name>``
        specify the name of your logfile.
        
        This implies ``%logstart`` at the beginning of your session
        
        generate a log file of all input. The file is named
        ipython_log.py in your current directory (which prevents logs
        from multiple IPython sessions from trampling each other). You
        can use this to later restore a session by loading your
        logfile with ``ipython -i ipython_log.py``

    ``--logplay=<name>``
    
      NOT AVAILABLE in 0.11

      you can replay a previous log. For restoring a session as close as
      possible to the state you left it in, use this option (don't just run
      the logfile). With -logplay, IPython will try to reconstruct the
      previous working environment in full, not just execute the commands in
      the logfile.

      When a session is restored, logging is automatically turned on
      again with the name of the logfile it was invoked with (it is
      read from the log header). So once you've turned logging on for
      a session, you can quit IPython and reload it as many times as
      you want and it will continue to log its history and restore
      from the beginning every time.
      
      Caveats: there are limitations in this option. The history
      variables _i*,_* and _dh don't get restored properly. In the
      future we will try to implement full session saving by writing
      and retrieving a 'snapshot' of the memory state of IPython. But
      our first attempts failed because of inherent limitations of
      Python's Pickle module, so this may have to wait.

    ``--[no-]messages``
	Print messages which IPython collects about its startup
	process (default on).

    ``--[no-]pdb``
	Automatically call the pdb debugger after every uncaught
	exception. If you are used to debugging using pdb, this puts
	you automatically inside of it after any call (either in
	IPython or in code called by it) which triggers an exception
	which goes uncaught.

    ``--[no-]pprint``
	ipython can optionally use the pprint (pretty printer) module
	for displaying results. pprint tends to give a nicer display
	of nested data structures. If you like it, you can turn it on
	permanently in your config file (default off).

    ``--profile=<name>``

	Select the IPython profile by name.
    
	This is a quick way to keep and load multiple
	config files for different tasks, especially if you use the
	include option of config files. You can keep a basic
	:file:`IPYTHON_DIR/profile_default/ipython_config.py` file 
	and then have other 'profiles' which
	include this one and load extra things for particular
	tasks. For example:

	1. $IPYTHON_DIR/profile_default : load basic things you always want.
	2. $IPYTHON_DIR/profile_math : load (1) and basic math-related modules.
	3. $IPYTHON_DIR/profile_numeric : load (1) and Numeric and plotting modules.

	Since it is possible to create an endless loop by having
	circular file inclusions, IPython will stop if it reaches 15
	recursive inclusions.

    ``InteractiveShell.prompt_in1=<string>``

	Specify the string used for input prompts. Note that if you are using
	numbered prompts, the number is represented with a '\#' in the
	string. Don't forget to quote strings with spaces embedded in
	them. Default: 'In [\#]:'.  The :ref:`prompts section <prompts>`
	discusses in detail all the available escapes to customize your
	prompts.

    ``InteractiveShell.prompt_in2=<string>``
	Similar to the previous option, but used for the continuation
	prompts. The special sequence '\D' is similar to '\#', but
	with all digits replaced dots (so you can have your
	continuation prompt aligned with your input prompt).  Default:
	' .\D.:' (note three spaces at the start for alignment with
	'In [\#]').

    ``InteractiveShell.prompt_out=<string>``
	String used for output prompts, also uses numbers like
	prompt_in1. Default: 'Out[\#]:'

    ``--quick``
        start in bare bones mode (no config file loaded).

    ``config_file=<name>``
	name of your IPython resource configuration file. Normally
	IPython loads ipython_config.py (from current directory) or
	IPYTHON_DIR/profile_default.

	If the loading of your config file fails, IPython starts with
	a bare bones configuration (no modules loaded at all).

    ``--[no-]readline``
	use the readline library, which is needed to support name
	completion and command history, among other things.  It is
	enabled by default, but may cause problems for users of
	X/Emacs in Python comint or shell buffers.

	Note that X/Emacs 'eterm' buffers (opened with M-x term) support
	IPython's readline and syntax coloring fine, only 'emacs' (M-x
	shell and C-c !) buffers do not.

    ``--TerminalInteractiveShell.screen_length=<n>``
	number of lines of your screen. This is used to control
	printing of very long strings. Strings longer than this number
	of lines will be sent through a pager instead of directly
	printed.

	The default value for this is 0, which means IPython will
	auto-detect your screen size every time it needs to print certain
	potentially long strings (this doesn't change the behavior of the
	'print' keyword, it's only triggered internally). If for some
	reason this isn't working well (it needs curses support), specify
	it yourself. Otherwise don't change the default.

    ``--TerminalInteractiveShell.separate_in=<string>``

	separator before input prompts.
	Default: '\n'

    ``--TerminalInteractiveShell.separate_out=<string>``
        separator before output prompts.
        Default: nothing.

    ``--TerminalInteractiveShell.separate_out2=<string>``
	separator after output prompts.
	Default: nothing.
	For these three options, use the value 0 to specify no separator.

    ``--nosep``
	shorthand for setting the above separators to empty strings.
	
	Simply removes all input/output separators.

    ``--init``
	allows you to initialize a profile dir for configuration when you
	install a new version of IPython or want to use a new profile.
	Since new versions may include new command line options or example
	files, this copies updated config files. Note that you should probably
	use %upgrade instead,it's a safer alternative.

    ``--version``    print version information and exit.

    ``--xmode=<modename>``

	Mode for exception reporting.

	Valid modes: Plain, Context and Verbose.

	* Plain: similar to python's normal traceback printing.
	* Context: prints 5 lines of context source code around each
	  line in the traceback.
	* Verbose: similar to Context, but additionally prints the
	  variables currently visible where the exception happened
	  (shortening their strings if too long). This can potentially be
	  very slow, if you happen to have a huge data structure whose
	  string representation is complex to compute. Your computer may
	  appear to freeze for a while with cpu usage at 100%. If this
	  occurs, you can cancel the traceback with Ctrl-C (maybe hitting it
	  more than once).

Interactive use
===============

IPython is meant to work as a drop-in replacement for the standard interactive
interpreter. As such, any code which is valid python should execute normally
under IPython (cases where this is not true should be reported as bugs). It
does, however, offer many features which are not available at a standard python
prompt. What follows is a list of these.


Caution for Windows users
-------------------------

Windows, unfortunately, uses the '\\' character as a path separator. This is a
terrible choice, because '\\' also represents the escape character in most
modern programming languages, including Python. For this reason, using '/'
character is recommended if you have problems with ``\``.  However, in Windows
commands '/' flags options, so you can not use it for the root directory. This
means that paths beginning at the root must be typed in a contrived manner
like: ``%copy \opt/foo/bar.txt \tmp``

.. _magic:

Magic command system
--------------------

IPython will treat any line whose first character is a % as a special
call to a 'magic' function. These allow you to control the behavior of
IPython itself, plus a lot of system-type features. They are all
prefixed with a % character, but parameters are given without
parentheses or quotes.

Example: typing ``%cd mydir`` changes your working directory to 'mydir', if it
exists.

If you have 'automagic' enabled (as it by default), you don't need
to type in the % explicitly. IPython will scan its internal list of
magic functions and call one if it exists. With automagic on you can
then just type ``cd mydir`` to go to directory 'mydir'. The automagic
system has the lowest possible precedence in name searches, so defining
an identifier with the same name as an existing magic function will
shadow it for automagic use. You can still access the shadowed magic
function by explicitly using the % character at the beginning of the line.

An example (with automagic on) should clarify all this:

.. sourcecode:: ipython

    In [1]: cd ipython # %cd is called by automagic

    /home/fperez/ipython

    In [2]: cd=1 # now cd is just a variable

    In [3]: cd .. # and doesn't work as a function anymore

    ------------------------------

        File "<console>", line 1

          cd ..

              ^

    SyntaxError: invalid syntax

    In [4]: %cd .. # but %cd always works

    /home/fperez

    In [5]: del cd # if you remove the cd variable

    In [6]: cd ipython # automagic can work again

    /home/fperez/ipython

You can define your own magic functions to extend the system. The
following example defines a new magic command, %impall:

.. sourcecode:: python

    ip = get_ipython()

    def doimp(self, arg):

        ip = self.api

        ip.ex("import %s; reload(%s); from %s import *" % (

        arg,arg,arg)

        )

    ip.expose_magic('impall', doimp)

Type `%magic` for more information, including a list of all available magic
functions at any time and their docstrings. You can also type
%magic_function_name? (see :ref:`below <dynamic_object_info` for information on
the '?' system) to get information about any particular magic function you are
interested in.

The API documentation for the :mod:`IPython.core.magic` module contains the full
docstrings of all currently available magic commands.


Access to the standard Python help
----------------------------------

As of Python 2.1, a help system is available with access to object docstrings
and the Python manuals. Simply type 'help' (no quotes) to access it. You can
also type help(object) to obtain information about a given object, and
help('keyword') for information on a keyword. As noted :ref:`here
<accessing_help>`, you need to properly configure your environment variable
PYTHONDOCS for this feature to work correctly.

.. _dynamic_object_info:

Dynamic object information
--------------------------

Typing ``?word`` or ``word?`` prints detailed information about an object. If
certain strings in the object are too long (docstrings, code, etc.) they get
snipped in the center for brevity. This system gives access variable types and
values, full source code for any object (if available), function prototypes and
other useful information.

Typing ``??word`` or ``word??`` gives access to the full information without
snipping long strings. Long strings are sent to the screen through the
less pager if longer than the screen and printed otherwise. On systems
lacking the less command, IPython uses a very basic internal pager.

The following magic functions are particularly useful for gathering
information about your working environment. You can get more details by
typing ``%magic`` or querying them individually (use %function_name? with or
without the %), this is just a summary:

    * **%pdoc <object>**: Print (or run through a pager if too long) the
      docstring for an object. If the given object is a class, it will
      print both the class and the constructor docstrings.
    * **%pdef <object>**: Print the definition header for any callable
      object. If the object is a class, print the constructor information.
    * **%psource <object>**: Print (or run through a pager if too long)
      the source code for an object.
    * **%pfile <object>**: Show the entire source file where an object was
      defined via a pager, opening it at the line where the object
      definition begins.
    * **%who/%whos**: These functions give information about identifiers
      you have defined interactively (not things you loaded or defined
      in your configuration files). %who just prints a list of
      identifiers and %whos prints a table with some basic details about
      each identifier.

Note that the dynamic object information functions (?/??, ``%pdoc``,
``%pfile``, ``%pdef``, ``%psource``) give you access to documentation even on
things which are not really defined as separate identifiers. Try for example
typing {}.get? or after doing import os, type ``os.path.abspath??``.

.. _readline:

Readline-based features
-----------------------

These features require the GNU readline library, so they won't work if your
Python installation lacks readline support. We will first describe the default
behavior IPython uses, and then how to change it to suit your preferences.


Command line completion
+++++++++++++++++++++++

At any time, hitting TAB will complete any available python commands or
variable names, and show you a list of the possible completions if
there's no unambiguous one. It will also complete filenames in the
current directory if no python names match what you've typed so far.


Search command history
++++++++++++++++++++++

IPython provides two ways for searching through previous input and thus
reduce the need for repetitive typing:

   1. Start typing, and then use Ctrl-p (previous,up) and Ctrl-n
      (next,down) to search through only the history items that match
      what you've typed so far. If you use Ctrl-p/Ctrl-n at a blank
      prompt, they just behave like normal arrow keys.
   2. Hit Ctrl-r: opens a search prompt. Begin typing and the system
      searches your history for lines that contain what you've typed so
      far, completing as much as it can.


Persistent command history across sessions
++++++++++++++++++++++++++++++++++++++++++

IPython will save your input history when it leaves and reload it next
time you restart it. By default, the history file is named
$IPYTHON_DIR/profile_<name>/history.sqlite. This allows you to keep
separate histories related to various tasks: commands related to
numerical work will not be clobbered by a system shell history, for
example.


Autoindent
++++++++++

IPython can recognize lines ending in ':' and indent the next line,
while also un-indenting automatically after 'raise' or 'return'.

This feature uses the readline library, so it will honor your
:file:`~/.inputrc` configuration (or whatever file your INPUTRC variable points
to). Adding the following lines to your :file:`.inputrc` file can make
indenting/unindenting more convenient (M-i indents, M-u unindents)::

    $if Python 
    "\M-i": "    "  
    "\M-u": "\d\d\d\d"  
    $endif

Note that there are 4 spaces between the quote marks after "M-i" above.

.. warning::

    Setting the above indents will cause problems with unicode text entry in
    the terminal.

.. warning::

    Autoindent is ON by default, but it can cause problems with the pasting of
    multi-line indented code (the pasted code gets re-indented on each line). A
    magic function %autoindent allows you to toggle it on/off at runtime. You
    can also disable it permanently on in your :file:`ipython_config.py` file
    (set TerminalInteractiveShell.autoindent=False).
    
    If you want to paste multiple lines, it is recommended that you use
    ``%paste``.


Customizing readline behavior
+++++++++++++++++++++++++++++

All these features are based on the GNU readline library, which has an
extremely customizable interface. Normally, readline is configured via a
file which defines the behavior of the library; the details of the
syntax for this can be found in the readline documentation available
with your system or on the Internet. IPython doesn't read this file (if
it exists) directly, but it does support passing to readline valid
options via a simple interface. In brief, you can customize readline by
setting the following options in your configuration file (note
that these options can not be specified at the command line):

    * **readline_parse_and_bind**: this option can appear as many times as
      you want, each time defining a string to be executed via a
      readline.parse_and_bind() command. The syntax for valid commands
      of this kind can be found by reading the documentation for the GNU
      readline library, as these commands are of the kind which readline
      accepts in its configuration file.
    * **readline_remove_delims**: a string of characters to be removed
      from the default word-delimiters list used by readline, so that
      completions may be performed on strings which contain them. Do not
      change the default value unless you know what you're doing.
    * **readline_omit__names**: when tab-completion is enabled, hitting
      <tab> after a '.' in a name will complete all attributes of an
      object, including all the special methods whose names include
      double underscores (like __getitem__ or __class__). If you'd
      rather not see these names by default, you can set this option to
      1. Note that even when this option is set, you can still see those
      names by explicitly typing a _ after the period and hitting <tab>:
      'name._<tab>' will always complete attribute names starting with '_'.
      
      This option is off by default so that new users see all
      attributes of any objects they are dealing with.

You will find the default values in your configuration file.


Session logging and restoring
-----------------------------

You can log all input from a session either by starting IPython with the
command line switch ``--logfile=foo.py`` (see :ref:`here <command_line_options>`)
or by activating the logging at any moment with the magic function %logstart.

Log files can later be reloaded by running them as scripts and IPython
will attempt to 'replay' the log by executing all the lines in it, thus
restoring the state of a previous session. This feature is not quite
perfect, but can still be useful in many cases.

The log files can also be used as a way to have a permanent record of
any code you wrote while experimenting. Log files are regular text files
which you can later open in your favorite text editor to extract code or
to 'clean them up' before using them to replay a session.

The `%logstart` function for activating logging in mid-session is used as
follows::

    %logstart [log_name [log_mode]]

If no name is given, it defaults to a file named 'ipython_log.py' in your
current working directory, in 'rotate' mode (see below).

'%logstart name' saves to file 'name' in 'backup' mode. It saves your
history up to that point and then continues logging.

%logstart takes a second optional parameter: logging mode. This can be
one of (note that the modes are given unquoted):

    * [over:] overwrite existing log_name.
    * [backup:] rename (if exists) to log_name~ and start log_name.
    * [append:] well, that says it.
    * [rotate:] create rotating logs log_name.1~, log_name.2~, etc.

The %logoff and %logon functions allow you to temporarily stop and
resume logging to a file which had previously been started with
%logstart. They will fail (with an explanation) if you try to use them
before logging has been started.

.. _system_shell_access:

System shell access
-------------------

Any input line beginning with a ! character is passed verbatim (minus
the !, of course) to the underlying operating system. For example,
typing ``!ls`` will run 'ls' in the current directory.

Manual capture of command output
--------------------------------

If the input line begins with two exclamation marks, !!, the command is
executed but its output is captured and returned as a python list, split
on newlines. Any output sent by the subprocess to standard error is
printed separately, so that the resulting list only captures standard
output. The !! syntax is a shorthand for the %sx magic command.

Finally, the %sc magic (short for 'shell capture') is similar to %sx,
but allowing more fine-grained control of the capture details, and
storing the result directly into a named variable. The direct use of 
%sc is now deprecated, and you should ise the ``var = !cmd`` syntax
instead.

IPython also allows you to expand the value of python variables when
making system calls. Any python variable or expression which you prepend
with $ will get expanded before the system call is made::

    In [1]: pyvar='Hello world' 
    In [2]: !echo "A python variable: $pyvar"  
    A python variable: Hello world

If you want the shell to actually see a literal $, you need to type it
twice::

    In [3]: !echo "A system variable: $$HOME"  
    A system variable: /home/fperez

You can pass arbitrary expressions, though you'll need to delimit them
with {} if there is ambiguity as to the extent of the expression::

    In [5]: x=10 
    In [6]: y=20 
    In [13]: !echo $x+y  
    10+y  
    In [7]: !echo ${x+y}  
    30

Even object attributes can be expanded::

    In [12]: !echo $sys.argv  
    [/home/fperez/usr/bin/ipython]


System command aliases
----------------------

The %alias magic function allows you to define magic functions which are in fact
system shell commands. These aliases can have parameters.

``%alias alias_name cmd`` defines 'alias_name' as an alias for 'cmd'

Then, typing ``%alias_name params`` will execute the system command 'cmd
params' (from your underlying operating system).

You can also define aliases with parameters using %s specifiers (one per
parameter). The following example defines the %parts function as an
alias to the command 'echo first %s second %s' where each %s will be
replaced by a positional parameter to the call to %parts::

    In [1]: alias parts echo first %s second %s 
    In [2]: %parts A B 
    first A second B  
    In [3]: %parts A  
    Incorrect number of arguments: 2 expected.  
    parts is an alias to: 'echo first %s second %s'

If called with no parameters, %alias prints the table of currently
defined aliases.

The %rehashx magic allows you to load your entire $PATH as
ipython aliases. See its docstring for further details.


.. _dreload:

Recursive reload
----------------

The dreload function does a recursive reload of a module: changes made
to the module since you imported will actually be available without
having to exit.


Verbose and colored exception traceback printouts
-------------------------------------------------

IPython provides the option to see very detailed exception tracebacks,
which can be especially useful when debugging large programs. You can
run any Python file with the %run function to benefit from these
detailed tracebacks. Furthermore, both normal and verbose tracebacks can
be colored (if your terminal supports it) which makes them much easier
to parse visually.

See the magic xmode and colors functions for details (just type %magic).

These features are basically a terminal version of Ka-Ping Yee's cgitb
module, now part of the standard Python library.


.. _input_caching:

Input caching system
--------------------

IPython offers numbered prompts (In/Out) with input and output caching
(also referred to as 'input history'). All input is saved and can be 
retrieved as variables (besides the usual arrow key recall), in 
addition to the %rep magic command that brings a history entry
up for editing on the next  command line.

The following GLOBAL variables always exist (so don't overwrite them!):

* _i, _ii, _iii: store previous, next previous and next-next previous inputs.
* In, _ih : a list of all inputs; _ih[n] is the input from line n. If you
  overwrite In with a variable of your own, you can remake the assignment to the
  internal list with a simple ``In=_ih``.

Additionally, global variables named _i<n> are dynamically created (<n>
being the prompt counter), so ``_i<n> == _ih[<n>] == In[<n>]``.

For example, what you typed at prompt 14 is available as _i14, _ih[14]
and In[14].

This allows you to easily cut and paste multi line interactive prompts
by printing them out: they print like a clean string, without prompt
characters. You can also manipulate them like regular variables (they
are strings), modify or exec them (typing ``exec _i9`` will re-execute the
contents of input prompt 9.

You can also re-execute multiple lines of input easily by using the
magic %macro function (which automates the process and allows
re-execution without having to type 'exec' every time). The macro system
also allows you to re-execute previous lines which include magic
function calls (which require special processing). Type %macro? for more details
on the macro system.

A history function %hist allows you to see any part of your input
history by printing a range of the _i variables.

You can also search ('grep') through your history by typing 
``%hist -g somestring``. This is handy for searching for URLs, IP addresses,
etc. You can bring history entries listed by '%hist -g' up for editing
with the %recall command, or run them immediately with %rerun.

.. _output_caching:

Output caching system
---------------------

For output that is returned from actions, a system similar to the input
cache exists but using _ instead of _i. Only actions that produce a
result (NOT assignments, for example) are cached. If you are familiar
with Mathematica, IPython's _ variables behave exactly like
Mathematica's % variables.

The following GLOBAL variables always exist (so don't overwrite them!):

    * [_] (a single underscore) : stores previous output, like Python's
      default interpreter.
    * [__] (two underscores): next previous.
    * [___] (three underscores): next-next previous.

Additionally, global variables named _<n> are dynamically created (<n>
being the prompt counter), such that the result of output <n> is always
available as _<n> (don't use the angle brackets, just the number, e.g.
_21).

These global variables are all stored in a global dictionary (not a
list, since it only has entries for lines which returned a result)
available under the names _oh and Out (similar to _ih and In). So the
output from line 12 can be obtained as _12, Out[12] or _oh[12]. If you
accidentally overwrite the Out variable you can recover it by typing
'Out=_oh' at the prompt.

This system obviously can potentially put heavy memory demands on your
system, since it prevents Python's garbage collector from removing any
previously computed results. You can control how many results are kept
in memory with the option (at the command line or in your configuration
file) cache_size. If you set it to 0, the whole system is completely
disabled and the prompts revert to the classic '>>>' of normal Python.


Directory history
-----------------

Your history of visited directories is kept in the global list _dh, and
the magic %cd command can be used to go to any entry in that list. The
%dhist command allows you to view this history. Do ``cd -<TAB>`` to
conveniently view the directory history.


Automatic parentheses and quotes
--------------------------------

These features were adapted from Nathan Gray's LazyPython. They are
meant to allow less typing for common situations.


Automatic parentheses
---------------------

Callable objects (i.e. functions, methods, etc) can be invoked like this
(notice the commas between the arguments)::

    >>> callable_ob arg1, arg2, arg3

and the input will be translated to this::

    -> callable_ob(arg1, arg2, arg3)

You can force automatic parentheses by using '/' as the first character
of a line. For example::

    >>> /globals # becomes 'globals()'

Note that the '/' MUST be the first character on the line! This won't work::

    >>> print /globals # syntax error

In most cases the automatic algorithm should work, so you should rarely
need to explicitly invoke /. One notable exception is if you are trying
to call a function with a list of tuples as arguments (the parenthesis
will confuse IPython)::

    In [1]: zip (1,2,3),(4,5,6) # won't work

but this will work::

    In [2]: /zip (1,2,3),(4,5,6) 
    ---> zip ((1,2,3),(4,5,6))  
    Out[2]= [(1, 4), (2, 5), (3, 6)]

IPython tells you that it has altered your command line by displaying
the new command line preceded by ->. e.g.::

    In [18]: callable list 
    ----> callable (list)


Automatic quoting
-----------------

You can force automatic quoting of a function's arguments by using ','
or ';' as the first character of a line. For example::

    >>> ,my_function /home/me # becomes my_function("/home/me")

If you use ';' instead, the whole argument is quoted as a single string
(while ',' splits on whitespace)::

    >>> ,my_function a b c # becomes my_function("a","b","c")

    >>> ;my_function a b c # becomes my_function("a b c")

Note that the ',' or ';' MUST be the first character on the line! This
won't work::

    >>> x = ,my_function /home/me # syntax error

IPython as your default Python environment
==========================================

Python honors the environment variable PYTHONSTARTUP and will execute at
startup the file referenced by this variable. If you put at the end of
this file the following two lines of code::

    from IPython.frontend.terminal.ipapp import launch_new_instance
    launch_new_instance()
    raise SystemExit

then IPython will be your working environment anytime you start Python.
The ``raise SystemExit`` is needed to exit Python when
it finishes, otherwise you'll be back at the normal Python '>>>'
prompt.

This is probably useful to developers who manage multiple Python
versions and don't want to have correspondingly multiple IPython
versions. Note that in this mode, there is no way to pass IPython any
command-line options, as those are trapped first by Python itself.

.. _Embedding:

Embedding IPython
=================

It is possible to start an IPython instance inside your own Python
programs. This allows you to evaluate dynamically the state of your
code, operate with your variables, analyze them, etc. Note however that
any changes you make to values while in the shell do not propagate back
to the running code, so it is safe to modify your values because you
won't break your code in bizarre ways by doing so.

This feature allows you to easily have a fully functional python
environment for doing object introspection anywhere in your code with a
simple function call. In some cases a simple print statement is enough,
but if you need to do more detailed analysis of a code fragment this
feature can be very valuable.

It can also be useful in scientific computing situations where it is
common to need to do some automatic, computationally intensive part and
then stop to look at data, plots, etc.
Opening an IPython instance will give you full access to your data and
functions, and you can resume program execution once you are done with
the interactive part (perhaps to stop again later, as many times as
needed).

The following code snippet is the bare minimum you need to include in
your Python programs for this to work (detailed examples follow later)::

    from IPython import embed

    embed() # this call anywhere in your program will start IPython

You can run embedded instances even in code which is itself being run at
the IPython interactive prompt with '%run <filename>'. Since it's easy
to get lost as to where you are (in your top-level IPython or in your
embedded one), it's a good idea in such cases to set the in/out prompts
to something different for the embedded instances. The code examples
below illustrate this.

You can also have multiple IPython instances in your program and open
them separately, for example with different options for data
presentation. If you close and open the same instance multiple times,
its prompt counters simply continue from each execution to the next.

Please look at the docstrings in the :mod:`~IPython.frontend.terminal.embed` 
module for more details on the use of this system.

The following sample file illustrating how to use the embedding
functionality is provided in the examples directory as example-embed.py.
It should be fairly self-explanatory:

.. literalinclude:: ../../examples/core/example-embed.py
    :language: python

Once you understand how the system functions, you can use the following
code fragments in your programs which are ready for cut and paste:

.. literalinclude:: ../../examples/core/example-embed-short.py
    :language: python

Using the Python debugger (pdb)
===============================

Running entire programs via pdb
-------------------------------

pdb, the Python debugger, is a powerful interactive debugger which
allows you to step through code, set breakpoints, watch variables,
etc.  IPython makes it very easy to start any script under the control
of pdb, regardless of whether you have wrapped it into a 'main()'
function or not. For this, simply type '%run -d myscript' at an
IPython prompt. See the %run command's documentation (via '%run?' or
in Sec. magic_ for more details, including how to control where pdb
will stop execution first.

For more information on the use of the pdb debugger, read the included
pdb.doc file (part of the standard Python distribution). On a stock
Linux system it is located at /usr/lib/python2.3/pdb.doc, but the
easiest way to read it is by using the help() function of the pdb module
as follows (in an IPython prompt)::

    In [1]: import pdb
    In [2]: pdb.help()

This will load the pdb.doc document in a file viewer for you automatically.


Automatic invocation of pdb on exceptions
-----------------------------------------

IPython, if started with the -pdb option (or if the option is set in
your rc file) can call the Python pdb debugger every time your code
triggers an uncaught exception. This feature
can also be toggled at any time with the %pdb magic command. This can be
extremely useful in order to find the origin of subtle bugs, because pdb
opens up at the point in your code which triggered the exception, and
while your program is at this point 'dead', all the data is still
available and you can walk up and down the stack frame and understand
the origin of the problem.

Furthermore, you can use these debugging facilities both with the
embedded IPython mode and without IPython at all. For an embedded shell
(see sec. Embedding_), simply call the constructor with
'--pdb' in the argument string and automatically pdb will be called if an
uncaught exception is triggered by your code.

For stand-alone use of the feature in your programs which do not use
IPython at all, put the following lines toward the top of your 'main'
routine::

    import sys
    from IPython.core import ultratb
    sys.excepthook = ultratb.FormattedTB(mode='Verbose',
    color_scheme='Linux', call_pdb=1)

The mode keyword can be either 'Verbose' or 'Plain', giving either very
detailed or normal tracebacks respectively. The color_scheme keyword can
be one of 'NoColor', 'Linux' (default) or 'LightBG'. These are the same
options which can be set in IPython with -colors and -xmode.

This will give any of your programs detailed, colored tracebacks with
automatic invocation of pdb.


Extensions for syntax processing
================================

This isn't for the faint of heart, because the potential for breaking
things is quite high. But it can be a very powerful and useful feature.
In a nutshell, you can redefine the way IPython processes the user input
line to accept new, special extensions to the syntax without needing to
change any of IPython's own code.

In the IPython/extensions directory you will find some examples
supplied, which we will briefly describe now. These can be used 'as is'
(and both provide very useful functionality), or you can use them as a
starting point for writing your own extensions.

.. _pasting_with_prompts:

Pasting of code starting with Python or IPython prompts
-------------------------------------------------------

IPython is smart enough to filter  out input prompts, be they plain Python ones
(``>>>`` and ``...``) or IPython ones (``In [N]:`` and `` ...:``).  You can
therefore copy and paste from existing interactive sessions without worry.

The following is a 'screenshot' of how things work, copying an example from the
standard Python tutorial::

    In [1]: >>> # Fibonacci series:

    In [2]: ... # the sum of two elements defines the next

    In [3]: ... a, b = 0, 1

    In [4]: >>> while b < 10:
       ...:     ...     print b
       ...:     ...     a, b = b, a+b
       ...:     
    1
    1
    2
    3
    5
    8

And pasting from IPython sessions works equally well::

    In [1]: In [5]: def f(x):
       ...:        ...:     "A simple function"
       ...:        ...:     return x**2
       ...:    ...: 

    In [2]: f(3)
    Out[2]: 9

.. _gui_support:

GUI event loop support
======================

.. versionadded:: 0.11
    The ``%gui`` magic and :mod:`IPython.lib.inputhook`.

.. warning::

   All GUI support with the ``%gui`` magic, described in this section, applies
   only to the plain terminal IPython, *not* to the Qt console.  The Qt console
   currently only supports GUI interaction via the ``--pylab`` flag, as
   explained :ref:`in the matplotlib section <matplotlib_support>`.

   We intend to correct this limitation as soon as possible, you can track our
   progress at issue #643_.

.. _643: https://github.com/ipython/ipython/issues/643
    
IPython has excellent support for working interactively with Graphical User
Interface (GUI) toolkits, such as wxPython, PyQt4, PyGTK and Tk. This is
implemented using Python's builtin ``PyOSInputHook`` hook. This implementation
is extremely robust compared to our previous thread-based version. The
advantages of this are:

* GUIs can be enabled and disabled dynamically at runtime.
* The active GUI can be switched dynamically at runtime.
* In some cases, multiple GUIs can run simultaneously with no problems.
* There is a developer API in :mod:`IPython.lib.inputhook` for customizing 
  all of these things.

For users, enabling GUI event loop integration is simple.  You simple use the
``%gui`` magic as follows::

    %gui [GUINAME]

With no arguments, ``%gui`` removes all GUI support.  Valid ``GUINAME``
arguments are ``wx``, ``qt4``, ``gtk`` and ``tk``.

Thus, to use wxPython interactively and create a running :class:`wx.App`
object, do::

    %gui wx

For information on IPython's Matplotlib integration (and the ``pylab`` mode)
see :ref:`this section <matplotlib_support>`.

For developers that want to use IPython's GUI event loop integration in the
form of a library, these capabilities are exposed in library form in the
:mod:`IPython.lib.inputhook` and :mod:`IPython.lib.guisupport` modules.
Interested developers should see the module docstrings for more information,
but there are a few points that should be mentioned here.

First, the ``PyOSInputHook`` approach only works in command line settings 
where readline is activated.  As indicated in the warning above, we plan on
improving the integration of GUI event loops with the standalone kernel used by
the Qt console and other frontends (issue 643_).

Second, when using the ``PyOSInputHook`` approach, a GUI application should
*not* start its event loop. Instead all of this is handled by the
``PyOSInputHook``. This means that applications that are meant to be used both
in IPython and as standalone apps need to have special code to detects how the
application is being run. We highly recommend using IPython's support for this.
Since the details vary slightly between toolkits, we point you to the various
examples in our source directory :file:`docs/examples/lib` that demonstrate
these capabilities.

.. warning::

   The WX version of this is currently broken.  While ``--pylab=wx`` works
   fine, standalone WX apps do not.  See
   https://github.com/ipython/ipython/issues/645 for details of our progress on
   this issue.


Third, unlike previous versions of IPython, we no longer "hijack" (replace
them with no-ops) the event loops. This is done to allow applications that
actually need to run the real event loops to do so. This is often needed to
process pending events at critical points.

Finally, we also have a number of examples in our source directory
:file:`docs/examples/lib` that demonstrate these capabilities.

PyQt and PySide
---------------

.. attempt at explanation of the complete mess that is Qt support

When you use ``--gui=qt`` or ``--pylab=qt``, IPython can work with either
PyQt4 or PySide.  There are three options for configuration here, because
PyQt4 has two APIs for QString and QVariant - v1, which is the default on
Python 2, and the more natural v2, which is the only API supported by PySide.
v2 is also the default for PyQt4 on Python 3.  IPython's code for the QtConsole
uses v2, but you can still use any interface in your code, since the
Qt frontend is in a different process.

The default will be to import PyQt4 without configuration of the APIs, thus
matching what most applications would expect. It will fall back of PySide if
PyQt4 is unavailable.

If specified, IPython will respect the environment variable ``QT_API`` used
by ETS.  ETS 4.0 also works with both PyQt4 and PySide, but it requires
PyQt4 to use its v2 API.  So if ``QT_API=pyside`` PySide will be used,
and if ``QT_API=pyqt`` then PyQt4 will be used *with the v2 API* for
QString and QVariant, so ETS codes like MayaVi will also work with IPython.

If you launch IPython in pylab mode with ``ipython --pylab=qt``, then IPython
will ask matplotlib which Qt library to use (only if QT_API is *not set*), via
the 'backend.qt4' rcParam.  If matplotlib is version 1.0.1 or older, then
IPython will always use PyQt4 without setting the v2 APIs, since neither v2
PyQt nor PySide work.

.. warning::

    Note that this means for ETS 4 to work with PyQt4, ``QT_API`` *must* be set
    to work with IPython's qt integration, because otherwise PyQt4 will be
    loaded in an incompatible mode.
    
    It also means that you must *not* have ``QT_API`` set if you want to
    use ``--gui=qt`` with code that requires PyQt4 API v1.


.. _matplotlib_support:

Plotting with matplotlib
========================

`Matplotlib`_ provides high quality 2D and 3D plotting for Python. Matplotlib
can produce plots on screen using a variety of GUI toolkits, including Tk,
PyGTK, PyQt4 and wxPython. It also provides a number of commands useful for
scientific computing, all with a syntax compatible with that of the popular
Matlab program.

To start IPython with matplotlib support, use the ``--pylab`` switch.  If no
arguments are given, IPython will automatically detect your choice of
matplotlib backend.  You can also request a specific backend with
``--pylab=backend``, where ``backend`` must be one of: 'tk', 'qt', 'wx', 'gtk',
'osx'.

.. _Matplotlib: http://matplotlib.sourceforge.net

.. _interactive_demos:

Interactive demos with IPython
==============================

IPython ships with a basic system for running scripts interactively in
sections, useful when presenting code to audiences. A few tags embedded
in comments (so that the script remains valid Python code) divide a file
into separate blocks, and the demo can be run one block at a time, with
IPython printing (with syntax highlighting) the block before executing
it, and returning to the interactive prompt after each block. The
interactive namespace is updated after each block is run with the
contents of the demo's namespace.

This allows you to show a piece of code, run it and then execute
interactively commands based on the variables just created. Once you
want to continue, you simply execute the next block of the demo. The
following listing shows the markup necessary for dividing a script into
sections for execution as a demo:

.. literalinclude:: ../../examples/lib/example-demo.py
    :language: python

In order to run a file as a demo, you must first make a Demo object out
of it. If the file is named myscript.py, the following code will make a
demo::

    from IPython.lib.demo import Demo

    mydemo = Demo('myscript.py')

This creates the mydemo object, whose blocks you run one at a time by
simply calling the object with no arguments. If you have autocall active
in IPython (the default), all you need to do is type::

    mydemo 

and IPython will call it, executing each block. Demo objects can be
restarted, you can move forward or back skipping blocks, re-execute the
last block, etc. Simply use the Tab key on a demo object to see its
methods, and call '?' on them to see their docstrings for more usage
details. In addition, the demo module itself contains a comprehensive
docstring, which you can access via::

    from IPython.lib import demo

    demo?

Limitations: It is important to note that these demos are limited to
fairly simple uses. In particular, you can not put division marks in
indented code (loops, if statements, function definitions, etc.)
Supporting something like this would basically require tracking the
internal execution state of the Python interpreter, so only top-level
divisions are allowed. If you want to be able to open an IPython
instance at an arbitrary point in a program, you can use IPython's
embedding facilities, see :func:`IPython.embed` for details.