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reference.txt
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reference.txt
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=================
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 ipythonrc configuration file for details on those. This file is 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 ipythonrc 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 ipythonrc 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 ipythonrc 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 sec. 6.4 <#sec:dyn-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 ~/.inputrc
configuration (or whatever file your INPUTRC variable points to). Adding
the following lines to your .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 ipythonrc 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 along with a corresponding detailed
explanation in your ipythonrc file.
Session logging and restoring
-----------------------------
You can log all input from a session either by starting IPython with the
command line switche ``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 and the alias option in the ipythonrc
configuration file allow 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 %rehash/rehashx magics allow you to load your entire $PATH as
ipython aliases. See their respective docstrings (or sec. 6.2
<#sec:magic> 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: stores previous input. _ii: next previous. _iii: next-next previous.
_ih : a list of all input _ih[n] is the input from line n and this list
is aliased to the global variable In. 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), such that
_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, 'exec In[9:14]+In[18]' will re-execute lines
9 through 13 and line 18).
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? or see
sec. 6.2 <#sec:magic> 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 also searches through the so called *shadow history*,
which remembers all the commands (apart from multiline code blocks)
you have ever entered. Handy for searching for svn/bzr URL's, IP adrresses
etc. You can bring shadow history entries listed by '%hist -g' up for editing
(or re-execution by just pressing ENTER) with %rep command. Shadow history
entries are not available as _iNUMBER variables, and they are identified by
the '0' prefix in %hist -g output. That is, history entry 12 is a normal
history entry, but 0231 is a shadow history entry.
Shadow history was added because the readline history is inherently very
unsafe - if you have multiple IPython sessions open, the last session
to close will overwrite the history of previountly closed session. Likewise,
if a crash occurs, history is never saved, whereas shadow history entries
are added after entering every command (so a command executed
in another IPython session is immediately available in other IPython
sessions that are open).
To conserve space, a command can exist in shadow history only once - it doesn't
make sense to store a common line like "cd .." a thousand times. The idea is
mainly to provide a reliable place where valuable, hard-to-remember commands can
always be retrieved, as opposed to providing an exact sequence of commands
you have entered in actual order.
Because shadow history has all the commands you have ever executed,
time taken by %hist -g will increase oven time. If it ever starts to take
too long (or it ends up containing sensitive information like passwords),
clear the shadow history by `%clear shadow_nuke`.
Time taken to add entries to shadow history should be negligible, but
in any case, if you start noticing performance degradation after using
IPython for a long time (or running a script that floods the shadow history!),
you can 'compress' the shadow history by executing
`%clear shadow_compress`. In practice, this should never be necessary
in normal use.
.. _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 ipythonrc
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