learnPython

IPython Installation and Implementation

IPython is an interactive command-line tool for the Python programming language. Some of the features include tab completion, shell syntax, data visualizations, tools for parallel computing. One of the more popular features is the browser-based IPython notebook which can combine code (and evaluate it), text, equations and plots all in one environment. The IPython notebook is similar to using Rstudio when writing code in the R programming language.

To start ipython (or ipython notebook) in a command line, use the ipython (ipython notebook) command

$ ipython

Each ipython notebook is comprised of many “cells” which can have code or text in it. To evaluate a cell, click the “play” button at the top of the notebook or click Shift + Enter.

Evaluating code in ipython

  • To evaluate code, use the <return>
  • Pressing will interrupt any code running
  • Use the %run command to evaluate a .py script inside of ipython (identical to running python myscript.py in command line)
%run myscript.py
%run -i myscript .py

The second line gives access to using variables defined in the ipython namespace

  • Use the %paste magic function to take whatever text is on the clipboard and execute it as a single block in the shell (i.e. overcomes code with unexpected indents or new lines)
  • Use the %cpaste magic function (similar to %paste) except you can paste as much code as you would like before evaluating it

Getting help in ipython

  • Tab completion can be used to complete any variables (objects, functions, modules, file paths)
  • Use the question mark (?) before or after any variable to get help about the object or show the docstring (documentation)
  • Use a double question mark (??) to show functions source code (if available)

IPython magic commands

As you saw above, ipython has a set of magic functions which are special commands that make programming in ipython significantly easier. To get help use %quickref or %magic.

For example, to delete all variables in the interactive namespace use %reset. To time a process use %timeit. To print the command input history, use %hist. To create a bookmark to save aliases for common directories, use %bookmark

%bookmark db ~/Dropbox/

Themes in IPython