scienceoss.com » IPython help

Run programs in the background in IPython

ryan — Sun, 02 Dec 2007 17:36:35 +0000

You can start another thread in IPython to run a program in the background.

bg go()	runs the function go() in another thread
jobs[0].status	tells you what’s going on with that job
jobs[0].result	the result of the job
jobs?	see more help on this part of IPython

Debug and optimize your code in IPython

ryan — Sun, 02 Dec 2007 17:34:22 +0000

One great thing about Python is the interactive debugger, which lets you inspect the value of variables at the point an error occurred. Of course, IPython integrates nicely with the Python debugger and makes debugging code a cinch.

xmode Plain	plain exception mode
xmode Context	shows source code around an error
xmode Verbose	alo shows the arguments going into the function where the error occured
pdb	Toggls automatic pdb. Upon hitting an error, you are dropped into the Python debugger. See {ln: Python debugger} for details.
run -d scriptName	starts the debugger from the beginning of the script
debug	go into the debugger right away.

IPython from any script

IPython can be embedded in a script. Wherever the command ipshell() occurs in your code, an IPython shell will pop up, giving you full access to everything in the namespace of the script. This is extremely useful if you want to add interactive functionality to a program, or need to check on some variables without using the debugger.

from IPython.Shell import IPShellEmbed 
ipshell = IPShellEmbed()
ipshell()  # add this wherever you would like to open an IPython window

Each ipshell() will open up a new shell. You have to close the newly opened shell using exit() or Exit before the script will continue.

Checking performance of your code

time sum(range(10000000))	time the summing of the list of numbers 1 through ten million and print how long it took
timeit sum(range(1000))	automatically figures out if it should try a couple times to get an accurate estimate for commands that take very little time. Prints average time.
prun go()	runs the profiler on the function, go(). The output from the profiler shows how long it took for each part of the script to run. prun works on expressions, not files.
run -p scriptname	runs the profiler on the script, "c">scriptname. run -p works on files, not statements.

Edit your code in IPython

ryan — Sun, 02 Dec 2007 17:31:39 +0000

IPython makes it easy to edit source code, or create new scripts based on a couple of lines in your history, or paste examples from the web.

edit script.py	Opens script.py in the default editor. NOTE: upon exit, the script executes
edit -x script.py	Opens script.py in the default editor. Upon exit, the script will not execute.
edit 1-3 6	Opens the default editor to edit commands 1, 2, 3, and 6 in the history
save apple 1-3, 5	Saves the history commands 1, 2, 3, and 5 in the file apple.py
cpaste	Tells IPython to expect code pasted from the clipboard. NOTE: type – on a line by itself to quit out of cpaste mode.

System commands from IPython

ryan — Sun, 02 Dec 2007 17:29:14 +0000

You can make use of your Python skills by interacting with system commands directly for things like file renaming, directory restructuring, or calling any arbitrary system command from within IPython. Here are some ways to do that.

!	at the beginning of a line, tells IPython this line is to be sent to the system shell
!ls	list directory (the magic function, ls, does the same thing)
patt = ‘*.py’	set up a Python variable, patt, which will be used in the examples below
!ls -l $patt	look for .py files using the -l format. The $ expands the Python variable to the shell.
!ls -l ${patt+c}	adds a c to the end of patt to make ls look for .pyc files. {} indicates a Python expression
alias	shows defined aliases, like ldir or ll
alias pr echo You Said: %s	define an alias called pr
pr HELLO	prints out “You Said HELLO” (executes the alias)
unalias pr	remove the alias pr

Note: The magic command, ls, can also be used to find .py files with the command ls *.py. However, more advanced usage, like passing Python variables and expressions or using options of the ls command (!ls -lha for example, to list the details of all files, including hidden ones, with human-readable sizes ) need to be done with the system command. The magic command is actually an alias for !ls -F. Using the system call form is the more general case, and can be used for any system calls.

Define a function to be used in the examples below:

def go(patt):  
    !ls -l $patt

go(‘*.py’)	looks for .py files using the go() function defined above
x = !ls	saves a list of the results of the system call to ls
len(x)	how many items were in the directory (where x = !ls as above)
x.s	displays the contents as a long string
x.l	displays as a list
x.n	display with newlines
x = !ls *.py \| sort	a sorted list of items ending with .py in the directory

Note: the list returned by a system call is not a standard Python list. Rather, it is a list of type IPython.genutils.SList which has the .s, .l, and other useful methods. Check out what it can do with x.[tab] (see introspection section, above).

Shortcuts in IPython

ryan — Sun, 02 Dec 2007 17:25:44 +0000

For the pathologically lazy, there are some shortcuts in IPython to save you from typing often-used commands.

p	short for print
page	prints long variables one page at a time
demo1 3,4	function call to demo1(): don’t have to use parentheses
,demo1 a,b	function call to demo1(): send arguments as strings ‘a’ and ‘b’
/demo2	function call to demo2(), a function with no input arguments
xyz(3,4);	semicolon suppresses output from xyz()‘s return statement

Running a program in IPython

ryan — Sun, 02 Dec 2007 17:16:05 +0000

Running programs or scripts in IPython is easy, and here are the commands to use.

run filename.py	runs the program "c">filename.py found in the present working directory
run python/filename.py	runs the program "c">filename.py found in the python directory under the present working directory
run -p filename	profile the script, "c">filename
run -d filename	run the script through the Python debugger, pdb
run?	show help for run . . . many useful options

Directory navigation in IPython

ryan — Sun, 02 Dec 2007 17:15:21 +0000

A reference table of commands to use when navigating directories in IPython.

pwd	display the present working directory
ls	list the contents of the present working directory
cd /tmp	move to the /tmp directory
cd ..	move up one directory
cd -	move to the last directory visited
bookmark mydir	save the current directory as mydir
bookmark mydir ../python	bookmarks the directory "c">../python (up one directory, then down into python) as mydir
cd mydir	change to the directory saved in the bookmark mydir
dhist	view a history of the directories you’ve been to
cd -2	change to the directory listed in position 2 in the directory history
pushd /usr/lib	push /usr/lib onto the directory stack
dirs	show directories in the directory stack

Getting help in IPython

ryan — Sun, 02 Dec 2007 17:04:08 +0000

IPython has an in-depth integrated help system. You can get help on IPython’s magic functions, view documentation from a single function, check out syntax-highlighted source code, or enter the Python interactive help system. Here’s a list of the commands to use.

lsmagic	lists the magic commands
?	(at the end of a function or variable) show help
??	(at the end of a function or object) show detailed help; often includes source code
help(sys)	online documentation for the sys module (sys must be imported first)
help(‘for’)	online doc for the for keyword
help()	enters the help system
topics	(at the help prompt) lists help topics. Type one to view it.
q	(at the help prompt) Exit the help system.

Import the re module (regular expression module) as an example for the commands below:

import re

pdef re.match	just the initialization expression for the re.match function
pdoc re.match	just the help text for re.match
pinfo re.match	same as using re.match? (shows help)
psource re.match	same as using re.match?? (shows detailed help)
pfile re.match	shows the contents of the file where the function is defined
pycat scriptName	displays the file, scriptName, in syntax-highlighted text
edit -x re.match	opens the source file for re.match in default editor