Overview
Teaching: 20 min
Exercises: 0 minQuestions
How can I use IPython for developing programs
Objectives
Explain what IPython is for.
Demonstrate key features of IPython.
IPython is an interactive shell for the Python programming language that offers enhanced introspection, additional shell syntax, tab completion and rich history. A good source of documentation for IPython can be found here.
To start IPython, type the ipython command in a terminal window.
$ ipython
Python 3.5.2 |Anaconda custom (x86_64)| (default, Jul 2 2016, 17:52:12)
Type "copyright", "credits" or "license" for more information.
IPython 4.2.0 -- An enhanced Interactive Python.
? -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help -> Python's own help system.
object? -> Details about 'object', use 'object??' for extra details.
In [1]:
Exiting IPython
To exit IPython and return to the shell, type
exitwhenever a prompt is visible. You’ll need to do this in order to edit a Python script with a text editor.In [1]: exit $
IPython can be used to write Python programs interactively, however the more usual
workflow is to use a text editor to edit your code, save the file, and load and run it
in IPython. You do this with the %run command. Let’s start by creating a simple
Python program:
$ nano simple.py
$ cat simple.py
def fib(n):
if n <= 1:
return n
else:
return(fib(n-1) + fib(n-2))
if __name__ == "__main__":
for i in range(10):
print(fib(i))
Now it can be run in IPython using %run:
$ ipython
Python 3.5.2 |Anaconda custom (x86_64)| (default, Jul 2 2016, 17:52:12)
Type "copyright", "credits" or "license" for more information.
IPython 4.2.0 -- An enhanced Interactive Python.
? -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help -> Python's own help system.
object? -> Details about 'object', use 'object??' for extra details.
In [1]: %run simple.py
0
1
1
2
3
5
8
13
21
34
In [2]: exit
$
It is also possible to pass variables defined in the IPython environment to
the program using the %run -i command. If we change the code to:
$ nano simple.py
$ cat simple.py
def fib(n):
if n <= 1:
return n
else:
return(fib(n-1) + fib(n-2))
if __name__ == "__main__":
for i in range(num_values): # get num_values from IPython
print(fib(i))
The we can set the num_values variable interactively in IPython, then run the program.
$ ipython
Python 3.5.2 |Anaconda custom (x86_64)| (default, Jul 2 2016, 17:52:12)
Type "copyright", "credits" or "license" for more information.
IPython 4.2.0 -- An enhanced Interactive Python.
? -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help -> Python's own help system.
object? -> Details about 'object', use 'object??' for extra details.
In [1]: num_values=5
In [2]: %run -i simple.py
0
1
1
2
3
In [3]: exit
$
IPython distinguishes commands from Python objects using the % symbol. So
%run means run the Python program supplied as an argument. IPython calls
these magic commands and provides many different commands. To see a list of
the available commands, use %lsmagic.
Tab Completion
Tab completion, especially for attributes, is a convenient way to explore the structure of any object you’re dealing with.
To use completion, type a pattern you would like the shell to match, followed by the
Tabkey.For example, to view an object’s attributes, type
object_name.followed by theTabkey.Besides Python objects and keywords, tab completion also works on file and directory names.
%automagic
By default, IPython will assume a command is a magic command unless there is a corresponding Python object with the same name. This means that it is possible to enter magic commands without the
%most of the time. The%automagicoption toggles between this behavior and requiring a%to be present if the command is a magic command.
Getting Help
Typing ‘?’ on its own will show an introduction and overview of IPython’s features.
The
%quickrefcommand shows a quick reference card with a lot of useful information about IPython magic commands.Typing an object name followed by a
?(i.e.object?) will show information about the object. Use??to get even more information.
IPython stores both the commands you enter, and the results that are produced. Only results from
statements or functions that are not assigned to variables are stored. It does not store the
output from print statements! You can easily go through previous
commands with the up- and down-arrow keys, or access your history in more sophisticated ways.
Input and output history are kept in variables called In and Out, keyed by the prompt numbers, e.g. In[4]
and Out[3]. The last three objects in output history are also kept in variables named _, _ _ and _ _ _.
You can treat these like any other Python variables, use them in expressions, etc.
$ ipython
Python 3.5.2 |Anaconda custom (x86_64)| (default, Jul 2 2016, 17:52:12)
Type "copyright", "credits" or "license" for more information.
IPython 4.2.0 -- An enhanced Interactive Python.
? -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help -> Python's own help system.
object? -> Details about 'object', use 'object??' for extra details.
In [1]: [1, 2, 3]
Out [1]: [1, 2, 3]
In [2]: var=33
In [3]: print(var)
33
In [4]: print(In[1])
[1, 2, 3]
In [5]: map(lambda x: x*2, 'ABC')
Out [5]: <map at 0x10410f208>
In [6]: print(list(Out[5]))
['AA', 'BB', 'CC']
In [7]: exit
$
You can use the %history magic function to examine past input and output. Input history from previous
sessions is saved in a database, and IPython can be configured to save output history.
Several other magic functions can use your input history, including %edit, %rerun, %recall, %macro,
%save and %pastebin.
It is possible to run any shell command from within IPython by prefixing the command with !. The output
from the command can also be captured by simply assigning it to a variable. Variables can also be passed to
the shell commands by prefixing the variable with a $. The following example shows each of these
features being used.
$ ipython
Python 3.5.2 |Anaconda custom (x86_64)| (default, Jul 2 2016, 17:52:12)
Type "copyright", "credits" or "license" for more information.
IPython 4.2.0 -- An enhanced Interactive Python.
? -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help -> Python's own help system.
object? -> Details about 'object', use 'object??' for extra details.
In [1]: !ping -c 1 google.com
PING google.com (172.217.1.78): 56 data bytes
64 bytes from 172.217.1.78: icmp_seq=0 ttl=56 time=14.319 ms
--- google.com ping statistics ---
1 packets transmitted, 1 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 14.319/14.319/14.319/0.000 ms
In [2]: files = !ls
In [3]: print(files[2])
Desktop
In [4]: file = files[2]
In [5]: !ls -l $file
total 97912
drwxr-xr-x@ 13 user 1551083765 442 Jan 25 17:06 data-shell
-rw-r--r--@ 1 user 1551083765 230351 Sep 29 22:13 doc.pages
drwxr-xr-x 4 user 1551083765 136 Jun 28 2016 iOSBackup
-rw-------@ 1 user 1551083765 41221 Jan 26 09:57 logo.png
drwxr-xr-x 28 user 1551083765 952 Feb 6 16:22 make-lesson
-rw-r--r--@ 1 user 1551083765 20097 Apr 26 2016 matmul.png
In [6]: exit
$
Key Points
IPython provides an interactive environment for developing Python programs