IPython - An Interactive Python Shell

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IPython - A Configurable Interactive Python Shell

IPython - A ConfigurableInteractive Python Shell

Finnbarr P. Murphy ([email protected])

Python is a popular interpretive object-orientated programming language that has been aroundsince the early 1990s and comes with its own command line shell. To make Python moreproductive for himself, Fernando Perez , currently a research scientist at U.C. Berkeley , created anenhanced version of the standard interactive Python shell which he called IPython .

IPython evolved from a number of then existing projects:

An existing project by Fernando Prez to add Mathematica-like prompts and a flexibleqconfiguration system to the standard Python interactive interpreter.An enhanced interactive Python prompt by Janko Hauser, called IPP, which maintained a promptqhistory which could be incrementally searched. It also had tab completion like many shellinterpreters and a help system which you could invoke using ?A project called LazyPython developed by Nathan Gray, who also developed the deep_reloadqmodule, which provided automatic quoting and parens, verbose tracebacks and shell escapesamongst other features.

According to a talk Perez gave at a SciPy conference in 2003, while at CU Bolder he merged hiscode and theirs as an afternoon hack in 2001 and six weeks later (with little sleep or thesisprogress) IPython version 0.1 was born.

Interestingly IPython started life under a GPL license but switched to a BSD license after version0.6.3. All new code contributions must now be licensed under the BSD license or a similar opensource license such as the MIT license. The current stable release is version 0.10.1. Officially,IPython 0.10.1 supports Python versions 2.5 and 2.6 but I use it with Python 2.7 withoutencountering any problems.

IPython is very popular within the scientific and research communities and is used in manyscientific packages and computer algebra systems such as SAGE and Singular .

Nowadays IPython consists of two main components:

An enhanced interactive shell.qAn architecture for interactive parallel computingq

Starting with version 0.9, IPython supports a wxPython based IPython GUI. IPython also supportsnon-blocking interaction with Tkinter , GTK , Qt, WX and even your own custom graphics librarieswhereas the standard Python shell only interacts with Tkinter which is is a thin object-orientedlayer on top of Tcl/Tk .

This post focuses on providing a quick introduction to the interactive command-line shell. Thisshell is a replacement for the Python interactive shell which tries to incorporate the most commonshell-like usage patterns in a natural way, while keeping 100% syntactic compatibility with the

Python language. Some of the features are simple time savers like automatic parenthesizes andtab completion. Others add capabilities such as profiles and editor use from within the shell.

The first time you invoke the IPython shell, it creates a configuration directory (called .ipython ) in

02-25-2011 Copyright 2004-2011 Finnbarr P. Murphy. All rights reserved. 1/9
http://blog.fpmurphy.com/2011/02/ipython.htmlhttp://blog.fpmurphy.com/2011/02/ipython.htmlhttp://www.python.org/http://fperez.org/http://berkeley.edu/http://ipython.scipy.org/http://www.scipy.org/http://www.colorado.edu/http://www.sagemath.org/http://www.singular.uni-kl.de/http://wiki.python.org/moin/TkInterhttp://www.gtk.org/http://qt.nokia.com/http://wxwidgets.org/http://tcl.sourceforge.net/http://tcl.sourceforge.net/http://wxwidgets.org/http://qt.nokia.com/http://www.gtk.org/http://wiki.python.org/moin/TkInterhttp://www.singular.uni-kl.de/http://www.sagemath.org/http://www.colorado.edu/http://www.scipy.org/http://ipython.scipy.org/http://berkeley.edu/http://fperez.org/http://www.python.org/http://blog.fpmurphy.com/2011/02/ipython.htmlhttp://blog.fpmurphy.com/2011/02/ipython.html


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your home directory.

$ ipython**********************************************************************Welcome to IPython. I will try to create a personal configuration directorywhere you can customize many aspects of IPython's functionality in:

/home/fpm/.ipythonInitializing from configuration: /usr/lib/python2.7/site-packages/IPython/UserConfig

Successful installation!

Please read the sections 'Initial Configuration' and 'Quick Tips' in theIPython manual (there are both HTML and PDF versions supplied with thedistribution) to make sure that your system environment is properly configuredto take advantage of IPython's features.

Important note: the configuration system has changed! The old system isstill in place, but its setting may be partly overridden by the settings in"~/.ipython/ipy_user_conf.py" config file. Please take a look at the file

if some of the new settings bother you.

Please press to start IPython.**********************************************************************Python 2.7 (r27:82500, Sep 16 2010, 18:02:00)Type "copyright", "credits" or "license" for more information.

IPython 0.10.1 -- An enhanced Interactive Python.? -> Introduction and overview of IPython's features.%quickref -> Quick reference.help -> Python's own help system.object? -> Details about 'object'. ?object also works, ?? prints more.

In [1]:

To exit the IPython shell, type Ctrl-D (which will request confirmation before editing) or either Exitor Quit (note the case!), both of which exit without prompting.

Here is a listing of what is created in your $HOME/.ipython subdirectory:

[fpm@ultra ~]$ ls -al .ipythontotal 80drwxr-xr-x 3 fpm fpm 4096 Feb 12 15:40 .drwx------. 53 fpm fpm 4096 Feb 12 15:40 ..drwxrwxr-x 3 fpm fpm 4096 Feb 12 15:40 db

-rw------- 1 fpm fpm 4 Feb 12 15:40 history-rw-r--r-- 1 fpm fpm 0 Jun 2 2010 __init__.py-rw-r--r-- 1 fpm fpm 150 Nov 14 21:26 __init__.pyc-rw-r--r-- 1 fpm fpm 150 Nov 14 21:26 __init__.pyo-rw-r--r-- 1 fpm fpm 24116 Feb 12 15:40 ipythonrc-rw-r--r-- 1 fpm fpm 1345 Feb 12 15:40 ipythonrc-math-rw-r--r-- 1 fpm fpm 2138 Feb 12 15:40 ipythonrc-numeric-rw-r--r-- 1 fpm fpm 1692 Feb 12 15:40 ipythonrc-physics-rw-r--r-- 1 fpm fpm 3602 Feb 12 15:40 ipythonrc-pysh-rw-r--r-- 1 fpm fpm 1260 Feb 12 15:40 ipythonrc-tutorial-rw-r--r-- 1 fpm fpm 3474 Jun 2 2010 ipy_user_conf.py-rw-r--r-- 1 fpm fpm 1742 Nov 14 21:26 ipy_user_conf.pyc-rw-r--r-- 1 fpm fpm 1742 Nov 14 21:26 ipy_user_conf.pyo[fpm@ultra ~]$

I have to say that one problem with IPython is the number of different types of configuration files.Originally IPython used ipythonrc -style key-value files. Then it switched to using ipy_user_conf.py



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-style configuration files but still kept support for ipythonrc files. Starting with IPython v0.11,which is currently under development, the IPython developers have introduced yet anothercompletely new configuration system that is designed from scratch to address the particular configuration needs of IPython .

One of the more interesting features of IPython is that it has a number of magic keywords(commands). It checks the command entered against its list of magic keywords. If the command isa magic keyword, IPython handles it. If its not a magic keyword, it passes the command off toPython to deal with. If automagic is on (the default), you do not need to prepend the % symbol to amagic keyword. If automagic is off, keywords must be prepended with the % symbol. Type magicat the shell prompt to see a list of all magic keywords together with descriptions of their usage.Type lsmagic at the shell prompt to see just a list of all the magic keywords.

In [1]: lsmagicAvailable magic functions:%Exit %Pprint %Quit %alias %autocall %autoindent %automagic %bg %bookmark %cd%clear %color_info %colors %cpaste %debug %dhist %dirs %doctest_mode %ed %edit%env %exit %hist %history %logoff %logon %logstart %logstate %logstop %lsmagic%macro %magic %p %page %paste %pdb %pdef %pdoc %pfile %pinfo %popd %profile%prun %psearch %psource %pushd %pwd %pycat %quickref %quit %r %rehash %rehashx%rep %reset %run %runlog %save %sc %store %sx %system_verbose %time %timeit%unalias %upgrade %who %who_ls %whos %xmode

Automagic is ON, % prefix NOT needed for magic functions.

In [2]:

In IPython, commands like cd or ls do what youd expect of them, while still allowing you to typenormal Python code. For example:

In [2]: ls100_2460.JPG* dia1.jpg hw* Music/ pf5.c.1 t2.js*10.xml dia2.jpg hwaddr* myimage/ pf5.c.2 temp.dat10.xsl dia3.jpg hwaddr1* myimage.img pfdemo* Templates/1.ksh* Documents/ hwaddr1.c new.jpg pfdemo.c test1.xml Downloads/ hwaddr.c newr.jpg Pictures/ t.js*arps* edk5.png i686 passwd Public/ tl*arps.c example1.js image/ perl/ qgis.sh* tmp/

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You can define your own magic functions. The following example defines a new magic commandcalled %stat :

def dostat(self, arg):"""Demonstrate a custom magic function."""ip = self.apiip.ex('import os; print os.stat("%s")' % arg)

ip.expose_magic('stat', dostat)

If you add the above lines to your $HOME/.ipython/ipy_user_conf.py (above main() ), you can stat

files directly from the command line.



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In [1]: stat file1posix.stat_result(st_mode=33204, st_ino=13895499, st_dev=64770L, st_nlink=1, st_uid=500, st_gid=500, st_size=0, st_atime=1297656251, st_mtime=1297656251, st_ctime=1297656251)

IPython supports custom modes called profiles . A profile is simply a configuration file that followsa specific naming convention and can be loaded using a specific syntax. The idea behind profiles isthat a user may want to maintain different configurations for different purposes, e.g. one for doingnumerical computing with NumPy and another for doing symbolic computing with SymPy .

Profiles ( custom modes ) make it easy to keep a separate configuration file for each of thesepurposes. The search path for profiles is the same as that of regular configuration files. The onlydifference is that profiles are named by simply adding _profilename to the end of the normalconfiguration file name. For example, if I wished to create a profile called fpm , I create aconfiguration file $HOME/.ipython/ipy_user_conf_fpm.py . A profile is loaded by means of the -pprofilename command line option.

One such profile which ships with IPython is called the shell profile and activates even moredefaults for shell-like behaviour. This mode can be invoked as follows:

$ ipython -p sh

System command list not initialized, probably the first run...running %rehashx to refresh the command list. Run %rehashxagain to refresh command list (after installing new software etc.)

IPython 0.10.1 [on Py 2.7]

[home/fpm]|1>Ctrl-D

$ ipython -p shIPython 0.10.1 [on Py 2.7][home/fpm]|1>

You can run any Python script and load all of its data directly into the interactive namespace usingthe %run magic command. This magic command supports flags for timing the execution of aPython script ( -t) and for executing them under the control of either the Python debugger ( -d) orprofiler ( -p).

In [1]: cat fibonacci.pydef fibonacci(n):

if n == 0:return 0

elif n == 1:return 1

else:return fibonacci(n-1) + fibonacci(n-2)

print fibonacci(8)

In [2]: run fibonacci21

In [3]: run -d fibonacciBreakpoint 1 at /home/fpm/fibonacci.py:1NOTE: Enter 'c' at the ipdb> prompt to start your script.

> (1)()

ipdb> c> /home/fpm/fibonacci.py(1)()



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1---> 1 def fibonacci(n):2 if n == 0:3 return 0

ipdb> q

In [4]: run -p fibonacci21

71 function calls (5 primitive calls) in 0.000 CPU seconds

Ordered by: internal time

ncalls tottime percall cumtime percall filename:lineno(function)1 0.000 0.000 0.000 0.000 {execfile}

67/1 0.000 0.000 0.000 0.000 fibonacci.py:1(fibonacci)1 0.000 0.000 0.000 0.000 fibonacci.py:1()1 0.000 0.000 0.000 0.000 :1()1 0.000 0.000 0.000 0.000 {method 'disable' of '_lsprof.Profiler' obje

cts}

In [5]:

Incidentally the %pdb magic command allows you to toggle on and off the automatic invocation of the IPython-enhanced pdb debugger.

To view your command line history (inputs), enter %hist at the prompt:

In [4]: histIn [4]: hist1: _ip.magic("lsmagic ")2: x = 1 + 63: print x4: _ip.magic("hist ")In [5]:

To display the inputs without numbers, use %hist -n . %hist -r will show inputs exactly as you typedthem. %history n1 n2 will print inputs between n1 and n2 (but excluding n2 ).

To access a single line in your history, you can use _i notation as shown below:

n [1]: 2+3Out[1]: 5

In [2]: 4+5Out[2]: 9

In [3]: 6+7Out[3]: 13

In [4]: _iOut[4]: u'6+7\n'

In [5]: _i3Out[5]: u'6+7\n'

Output results are automatically stored in a global dictionary named Out and variables named _1,_2, and so on alias them. Additionally, the three variables named _, __ and ___ always contain thelast three results.

In [1]: 4+5



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Out[1]: 9

In [2]: 6*3Out[2]: 18

In [3]: Out[1]Out[3]: 9

In [4]: _1Out[4]: 9

In [5]: _2Out[5]: 18

In [6]: ___Out[6]: 9

If a command begins with two exclamation marks, the command is executed but its output iscaptured and returned as a python list, split on newlines. The !! syntax is a shorthand for the %sxmagic command.

In [1]: lsfile1 file2 file3 file4

In [2]: !!lsOut[2]: SList (.p, .n, .l, .s, .grep(), .fields(), sort() available):0: file11: file22: file33: file4

Another useful feature of IPython is that it can automatically add quotations to strings and

parentheses to functions and methods.

In [5]: str='www.example.com'In [6]: ,str.lstrip cmowz.-------> str.lstrip("cmowz.")Out[6]: 'example.com'

In [7]: min 1,2------> min(1,2)Out[7]: 1

You can log your IPython session using the command line option -log which creates the fileipython_log.py in the current directory or you can use the command line option -logfile to specifyyour own filename. To resume a session enter ipython -logplay [file] .

Within a session the %logstart , %logoff and %logon keywords allow you to create session log andstop and start session logging.

In [1]: logstartActivating auto-logging. Current session state plus future input saved.Filename : ipython_log.pyMode : rotateOutput logging : FalseRaw input log : FalseTimestamping : FalseState : active



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In [2]: logonLogging is already ON

In [3]: logoffSwitching logging OFF

In [4]: hist1: _ip.magic("logstart ")

2: _ip.magic("logon ")3: _ip.magic("logoff ")4: _ip.magic("hist ")

In [5]: logonSwitching logging ON

You can also customize your IPython shell prompt. The syntax for doing this is similar to that usedin the Bash shell. The following are the default IPython prompts:

prompt_in1 'In [\#]:'

prompt_in2 ' .\D.:'prompt_out 'Out[\#]:'

You can change the prompt to your liking by editing $HOME/.ipyton/ipy_user_conf.py . Forexample, here is my configuration:

o.prompt_in1 = r'\W \#> 'o.prompt_in2 = r'\W \D> 'o.prompt_out = r'\W \#> '

which produces the following prompts when IPython is invoked:

$ ipython -p shIPython 0.10.1 [on Py 2.7].ipython 1> lsdb/ __init__.py ipythonrc-math ipythonrc-tutorialhistory __init__.pyc ipythonrc-numeric ipy_user_conf.pyhistory-pysh __init__.pyo ipythonrc-physics ipy_user_conf.pychistory-sh ipythonrc ipythonrc-pysh ipy_user_conf.pyo.ipython 2> max 3,4----------> max(3,4).ipython 2> 4.ipython 3> Ctrl_D

$

Ipython makes it easier to work with objects. With Python the dir function is used to list all theattributes of an object. For example:

>>> import Crypto>>> dir(Crypto)['__all__', '__builtins__', '__doc__', '__file__', '__name__', '__package__', '__path__','__revision__', '__version__', 'version_info']>>>

IPython has a set of special functions for providing more information about an object. Typingobject_name? will print all sorts of details about any object, including docstrings, functiondefinitions and class constructor details. For example, Crypto? or ?Crypto (either way will work)



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outputs detailed information about the Crypto module.

In [12]: import Crypto

In [13]: ? CryptoType: module

Base Class:String Form:Namespace: InteractiveFile: /usr/lib64/python2.7/site-packages/Crypto/__init__.pyDocstring:

Python Cryptography Toolkit

A collection of cryptographic modules implementing various algorithmsand protocols.

Subpackages:Crypto.Cipher Secret-key encryption algorithms (AES, DES, ARC4)Crypto.Hash Hashing algorithms (MD5, SHA, HMAC)Crypto.Protocol Cryptographic protocols (Chaffing, all-or-nothing

transform). This package does not contain anynetwork protocols.Crypto.PublicKey Public-key encryption and signature algorithms

(RSA, DSA)Crypto.Util Various useful modules and functions (long-to-string

conversion, random number generation, numbertheoretic functions)

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There are also a number of magic commands for retrieving specific information as shown in thefollowing example.

In [1]: import printer

In [2]: %psource printer"""This function call print"""def printer(x):

print xprintstatus = 1

In [3]: %pdoc printerThis function call print

In [4]: %pdef printerObject is not callable.

Entering complex code or nested structures into the interpreter can be difficult with onlysingle-line editing. The %edit magic keyword enables multiline editing by opening the editordefined by the environment variable $EDITOR or within your configuration files. If $EDITOR is notdefined, IPython defaults to using vim on GNU/Linux.

When you call %edit (%ed is an alias) with no arguments, IPython opens an editor with atemporary empty file, executes the contents of the temporary file upon closing the editor and itreturns the contents of the file as a string variable. If you do not want the contents of thetemporary file to be executed upon editor exit, use %edit -x .

In [4] %edIPython will make a temporary file named: /tmp/ipython_edit_RcMZ4_.pyEditing... done. Executing edited code...



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output is 4Out[4]: 'print "output is ", 2 + 2\n'In [8]: %ed -xIn [5] %ed -xIPython will make a temporary file named: /tmp/ipython_edit_OMkEok.pyEditing...Out[5]: 'print "output is ", 2 + 2\n'

On GNU/Linux the temporary file is created in the /tmp directory rather than the /var/tmpdirectory. So far, I have not found a way to change the pathname of the temporary file but thereprobably is some way of doing it.

By the way, IPython is not the only enhanced shell for Python. One of the more popularalternatives is bpython which features syntax highlighting, code completion, expected parameters,rewind, save work to file and pastebin support. Others include DreamPie and enhanced shellsincluded in Python IDEs such as the SPE IDE .

Finally I am moved to once again point out that the Internet is becoming filled with rubbish andincorrect information. While researching IPython examples for this post, I came across moreobsolete and incorrect information about IPython than correct information. This is becauseIPython has significantly changed since inception in areas such as configuration files and magicfunction definitions but documentation and examples relating to obsolete versions of IPython stilllitter the Internet. Perhaps there needs to be a mechanism for removing obsolete information fromthe Internet or at least clearly marking it as obsolete.

I have barely scratched the surface of all the features in IPython but I need to finish this post. If you are a Python developer, I strongly encourage you to switch to IPython and enjoy the resultingproductivity gains.

http://bpython-interpreter.org/http://dreampie.sourceforge.net/http://pythonide.stani.be/http://pythonide.stani.be/http://dreampie.sourceforge.net/http://bpython-interpreter.org/