IPython3 (Notes)

IPython3 provides a series of advantages over the standard Python shell - in particular with regard to scientific computing. A good start is too look into the IPython documentation. Start by making sure it is properly installed:

$ sudo apt install ipython3 python3-ipdb ipython3-qtconsole ipython3-notebook

IPython can be started via eg.

$ ipython3
$ ipython3 qtconsole --pylab=inline
$ ipython3 notebook --pylab=inline

However, I prefer adding an alias to start it with less typing. This can, for example, be achieved by

$ echo "alias i='ipython3'" >> ~/.bashrc

Shortcuts

_, __

last, second last output

_i[X] / _[X]

input / output number X

var = !command

execute operating system shell command and store output in var

!command $var

use content of Python variable var as arguments to operating system command

Magic Functions

One of IPython's key features are so-called magic functions. They are helpful when Python would not be natural / straight-forward in solving a problem. Examples include %cpaste, %paste and . Refer to the documentation (%quickref) for more. It is possible to obtain help for the magic functions by appending a ? directly after their name.

%cpaste

Open a special prompt for manually pasting Python code to be executed

%debug

Invoke post mortem debugger

%hist

Print command input history for copying to an editor

%logstart

Create log of entire console session

%paste

Execute pre-formatted Python code from clipboard

%pdb

Automatically enter debugger after any exception

%quickref

Display the IPython Quick Reference Card

%run [-d] script.py

Run passed script inside IPython (-d enables the debugger); -p -s cumulative runs the script with profiling enabled.

%timeit statement

Time execution of a Python statement or expression. It has a heuristic to run the statement multiple times to produce a fairly reliable average runtime.

%prun statement

Run a statement through the python code profiler

ipdb

IPython's integrated debugger. Allows inspecting the status of variable by simply typing their name. Should their name overlap with a debugger command, the latter takes precedence. To be able to still access the variable, type

!varname

Inside the debugger, simply type h for help. If you have trouble getting out of the debugger, the following should help

import os
os._exit(0)

For debugging a function available inside ipython, the following snipped (kudos to Wes McKinney) will be helpful

def debug(f, *args, **kwargs):
    from IPython.core.debugger import Pdb
    pdb = Pdb(color_scheme='Linux')
    return pdb.runcall(f, *args, **kwargs)