IPython

Tips & Tricks

2 kinds of Pythonistas

Live demo #1

I've decided that the best way to show you the capabilities of IPython is with a short live demo. This is how those demos usually ends. Nevertheless, let's give it a try.
So let's start the IPython REPL
OFFLINE NOTES:
increase the font !
import requests ->TAB # Let's import a random module, you can see that pressing TAB gives you the auto completion
requests.get? # Adding a question mark will show you the doc string of that function
requests.get?? # Adding two question marks will show you the whole body of a function
requests.cookies # It works also with classes or modules

%magic

%edit


def hello(name):
    print 'Hello', name '!'

So, what happens if I paste this code into IPython ? Well, I get an error, cause I forgot the comma. I could press arrow up and try to fix it, but when the function has multiple lines this can become quite a hassle. So we can use a magic function called %edit. It will open your favorite text editor (or Vim, if you haven't configured it) and allow you to edit your code there. After you save and exit, it will execute the code. I could write my function here, but I'm too lazy to do this. Instead, I can use the %edit command and specify a line number, and this line will be automatically copied inside the editor. There is also another great feature of %edit command, if you run if with -p option, it will reopen the same file as last time. So you can keep iterating on your function until you fix all the errors.

%debug


def hello(name):
    print 'Hello', name, '!'
    print number + 42

But what happens if the function is more complicated and I don't see the error right away ?
IPython has a nice function that you can use in this case, called %debug.
It will automatically find the error in the code and fix it for you. How cool is that ? No, I'm kidding, it won't do that (yet!), instead it will start the debugger session in the place where the error has occurred, so you can poke around and find the error. So, let's see what is the problem.
Name is defined...
Ahh, but the number is not defined.
I could now use the %edit command to fix it, but let's continue with another example.

%cpaste


def hello(name):
    print 'Hello', name, '!'
    print number + 42
number = 0

%timeit function()

%pastebin 10-20
# 'https://gist.github.com/8f03e623fe366'

%macro foo 10-20

%save foo.py 10-20

There are many more interesting functions in IPython, I will just quickly show a few:
- you can use %timeit to measure the execution time of a function
- if you think that some code is worth sharing, you can use %pastebin command. It creates a gist on github with lines 10-20 and return the URL that you can share with your colleagues.
- you can save some lines as a macro with %macro command. This command will save lines 10-20 as a macro called foo, so each time you type foo, it will execute those 10 lines.
- and if you are particularly happy with some code you just wrote, you can save it to a file with %save command. This example with save lines 10-20 in a file called foo.py.

Shell commands:

ls
pwd
cd ..
!ping www.google.com

Debugging your code with IPython:

some code
import IPython; IPython.embed()
some other code that fails

Summary

Tab completion
Easy access to documentation with ? and ??
%magic function
Shell commands
Debugging

Where can I get it ?

http://ipython.org/install.html