ipython¶

ipython is an interactive version of the python interpreter. It provides a number of extras which are helpful when writing code. ipython code is almost always python code, and the differences are generally only important when editing a code in a live (interactive) environment.

The jupyter notebook is a fine example of an interactive environment - you are changing the code as it runs and checking answers as you go. Because you may have a lot of half-completed results in an interactive script, you probably want to make as few mistakes as you can. This is the purpose of ipython.

ipython provides access to the help / documentation system, provides tab completion of variable and function names, allows you see see what methods live inside a module …

## Try the autocomplete ... it works on functions that are in scope

#print

# it also works on variables

long_but_helpful_variable_name = 1

long_but_helpful_variable_name

It works on modules to list the available methods and variables. Take the math module, for example:

import math

math.isinf  # Try completion on this

help(math.isnan)

# try math.isinf() and hit shift-tab while the cursor is between the parentheses 
# you should see the same help pop up.

# math.isinf()

It works on functions that take special arguments and tells you what you need to supply.

Try this and try tabbing in the parenthesis when you use this function yourself:

import string
string.capwords("the quality of mercy is not strained")

string.capwords()

It also provides special operations that allow you to drill down into the underlying shell / filesystem (but these are not standard python code any more).

# execute simple unix shell commands 

!ls

!echo ""

!pwd

Another way to do this is to use the cell magic functionality to direct the notebook to change the cell to something different (here everything in the cell is interpreted as a unix shell )

%%sh 

ls -l

echo ""

pwd

I don’t advise using this too often as the code becomes more difficult to convert to python.

A % is a one-line magic function that can go anywhere in the cell.
A %% is a cell-wide function

%magic  # to see EVERYTHING in the magic system !

Useful magic functions:

%matplotlib inline makes plots appear in the notebook and not an external window
%run FILE runs the contents of the file in place of the given cell
%%timeit times how long the cell takes to run

You can also run ipython in the terminal / shell on this machine. You will see that some of the interactivity still works in a text environment but not all of the pop up help is as helpful as in the notebooks.

Terminal

EMSC 4033 Computational Geoscience

ipython

ipython¶