When executing code in IPython, all valid Python syntax works as-is, but IPython provides a number of features designed to make the interactive experience more fluid and efficient.
In the notebook, to run a cell of code, hit Shift-Enter. This executes the cell and puts the cursor in the next cell below, or makes a new one if you are at the end. Alternately, you can use:
Alt-Enter to force the creation of a new cell unconditionally (useful when inserting new content in the middle of an existing notebook).Control-Enter executes the cell and keeps the cursor in the same cell, useful for quick experimentation of snippets that you don't need to keep permanently.
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print "Hi"
Getting help:
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?
Typing object_name? will print all sorts of details about any object, including docstrings, function definition lines (for call arguments) and constructor details for classes.
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import collections
collections.namedtuple?
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collections.Counter??
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*int*?
An IPython quick reference card:
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%quickref
Tab completion, especially for attributes, is a convenient way to explore the structure of any object you’re dealing with. Simply type object_name.<TAB> to view the object’s attributes. Besides Python objects and keywords, tab completion also works on file and directory names.
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collections.
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2+10
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_+10
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You can suppress the storage and rendering of output if you append ; to the last cell (this comes in handy when plotting with matplotlib, for example):
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10+20;
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_
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The output is stored in _N and Out[N] variables:
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_10 == Out[10]
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And the last three have shorthands for convenience:
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print 'last output:', _
print 'next one :', __
print 'and next :', ___
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_i
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_ii
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print 'last input:', _i
print 'next one :', _ii
print 'and next :', _iii
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%history -n 1-5
Exercise
Write the last 10 lines of history to a file named log.py.
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!pwd
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files = !ls
print "My current directory's files:"
print files
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!echo $files
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!echo {files[0].upper()}
Note that all this is available even in multiline blocks:
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import os
for i,f in enumerate(files):
if f.endswith('ipynb'):
!echo {"%02d" % i} - "{os.path.splitext(f)[0]}"
else:
print '--'
The IPyhton 'magic' functions are a set of commands, invoked by prepending one or two % signs to their name, that live in a namespace separate from your normal Python variables and provide a more command-like interface. They take flags with -- and arguments without quotes, parentheses or commas. The motivation behind this system is two-fold:
To provide an orthogonal namespace for controlling IPython itself and exposing other system-oriented functionality.
To expose a calling mode that requires minimal verbosity and typing while working interactively. Thus the inspiration taken from the classic Unix shell style for commands.
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%magic
Line vs cell magics:
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%timeit range(10)
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%%timeit
range(10)
range(100)
Line magics can be used even inside code blocks:
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for i in range(5):
size = i*100
print 'size:',size,
%timeit range(size)
Magics can do anything they want with their input, so it doesn't have to be valid Python:
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%%bash
echo "My shell is:" $SHELL
echo "My memory status is:"
free
Another interesting cell magic: create any file you want locally from the notebook:
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%%writefile test.txt
This is a test file!
It can contain anything I want...
And more...
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!cat test.txt
Let's see what other magics are currently defined in the system:
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%lsmagic
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Not only can you input normal Python code, you can even paste straight from a Python or IPython shell session:
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>>> # Fibonacci series:
... # the sum of two elements defines the next
... a, b = 0, 1
>>> while b < 10:
... print b
... a, b = b, a+b
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In [1]: for i in range(10):
...: print i,
...:
And when your code produces errors, you can control how they are displayed with the %xmode magic:
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%%writefile mod.py
def f(x):
return 1.0/(x-1)
def g(y):
return f(y+1)
Now let's call the function g with an argument that would produce an error:
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import mod
mod.g(0)
Since 1.0 the IPython notebook web application support raw_input which for example allow us to invoke the %debug magic in the notebook:
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mod.g(0)
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%debug
Don't foget to exit your debugging session. Raw input can of course be use to ask for user input:
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enjoy = raw_input('Are you enjoying this tutorial ?')
print 'enjoy is :', enjoy
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%%perl
@months = ("July", "August", "September");
print $months[0];
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%%ruby
name = "world"
puts "Hello #{name.capitalize}!"
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%connect_info
We can connect automatically a Qt Console to the currently running kernel with the %qtconsole magic, or by typing ipython console --existing <kernel-UUID> in any terminal:
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%qtconsole