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.print "Hi"
Hi
Getting help:
?
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.
import collections
collections.namedtuple?
collections.Counter??
*int*?
An IPython quick reference card:
%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.
collections.
2+10
12
_+10
22
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):
10+20;
_
22
The output is stored in _N
and Out[N]
variables:
_10 == Out[10]
True
And the last three have shorthands for convenience:
print 'last output:', _
print 'next one :', __
print 'and next :', ___
last output: True next one : 22 and next : 22
In[11]
u'_10 == Out[10]'
_i
u'In[11]'
_ii
u'In[11]'
print 'last input:', _i
print 'next one :', _ii
print 'and next :', _iii
last input: _ii next one : _i and next : In[11]
%history -n 1-5
1: print "Hi" 2: ? 3: import collections collections.namedtuple? 4: collections.Counter?? 5: *int*?
Exercise
Write the last 10 lines of history to a file named log.py
.
!pwd
/home/fperez/teach/astro-hack-week/day1/ipython
files = !ls
print "My current directory's files:"
print files
My current directory's files: ['Beyond Plain Python.ipynb', 'Converting Notebooks With nbconvert.ipynb', 'Custom Display Logic.ipynb', 'images', 'Notebook Basics.ipynb', 'Rich Output.ipynb', 'Using Interact.ipynb', 'Working With Markdown Cells.html', 'Working With Markdown Cells.ipynb', 'Working With Markdown Cells.pdf', 'Working With Markdown Cells.tex']
!echo $files
[Beyond Plain Python.ipynb, Converting Notebooks With nbconvert.ipynb, Custom Display Logic.ipynb, images, Notebook Basics.ipynb, Rich Output.ipynb, Using Interact.ipynb, Working With Markdown Cells.html, Working With Markdown Cells.ipynb, Working With Markdown Cells.pdf, Working With Markdown Cells.tex]
!echo {files[0].upper()}
BEYOND PLAIN PYTHON.IPYNB
Note that all this is available even in multiline blocks:
import os
for i,f in enumerate(files):
if f.endswith('ipynb'):
!echo {"%02d" % i} - "{os.path.splitext(f)[0]}"
else:
print '--'
00 - Beyond Plain Python 01 - Converting Notebooks With nbconvert 02 - Custom Display Logic -- 04 - Notebook Basics 05 - Rich Output 06 - Using Interact -- 08 - Working With Markdown Cells -- --
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.
%magic
Line vs cell magics:
%timeit range(10)
1000000 loops, best of 3: 195 ns per loop
%%timeit
range(10)
range(100)
1000000 loops, best of 3: 832 ns per loop
Line magics can be used even inside code blocks:
for i in range(5):
size = i*100
print 'size:',size,
%timeit range(size)
size: 010000000 loops, best of 3: 122 ns per loop size: 1001000000 loops, best of 3: 651 ns per loop size: 2001000000 loops, best of 3: 1.1 µs per loop size: 3001000000 loops, best of 3: 1.74 µs per loop size: 400100000 loops, best of 3: 2.66 µs per loop
Magics can do anything they want with their input, so it doesn't have to be valid Python:
%%bash
echo "My shell is:" $SHELL
echo "My memory status is:"
free
My shell is: /bin/bash My memory status is: total used free shared buffers cached Mem: 7870496 7077772 792724 265364 442596 2153668 -/+ buffers/cache: 4481508 3388988 Swap: 3905532 20552 3884980
Another interesting cell magic: create any file you want locally from the notebook:
%%writefile test.txt
This is a test file!
It can contain anything I want...
And more...
Writing test.txt
!cat test.txt
This is a test file! It can contain anything I want... And more...
Let's see what other magics are currently defined in the system:
%lsmagic
Available line magics: %alias %alias_magic %autocall %automagic %autosave %bookmark %cat %cd %cl %clear %clk %colors %config %connect_info %cp %d %dd %debug %dhist %dirs %dl %doctest_mode %dx %ed %edit %env %gui %hist %history %install_default_config %install_ext %install_profiles %killbgscripts %ldir %less %lf %lk %ll %load %load_ext %loadpy %logoff %logon %logstart %logstate %logstop %ls %lsmagic %lx %macro %magic %man %matplotlib %mkdir %more %mv %notebook %page %pastebin %pdb %pdef %pdoc %pfile %pinfo %pinfo2 %popd %pprint %precision %profile %prun %psearch %psource %pushd %pwd %pycat %pylab %qtconsole %quickref %recall %rehashx %reload_ext %rep %rerun %reset %reset_selective %rm %rmdir %run %save %sc %store %sx %system %tb %time %timeit %unalias %unload_ext %who %who_ls %whos %xdel %xmode Available cell magics: %%! %%HTML %%SVG %%bash %%capture %%debug %%file %%html %%javascript %%latex %%perl %%prun %%pypy %%python %%python2 %%python3 %%ruby %%script %%sh %%svg %%sx %%system %%time %%timeit %%writefile Automagic is ON, % prefix IS NOT needed for line magics.
Not only can you input normal Python code, you can even paste straight from a Python or IPython shell session:
>>> # Fibonacci series:
... # the sum of two elements defines the next
... a, b = 0, 1
>>> while b < 10:
... print b
... a, b = b, a+b
1 1 2 3 5 8
In [1]: for i in range(10):
...: print i,
...:
0 1 2 3 4 5 6 7 8 9
And when your code produces errors, you can control how they are displayed with the %xmode
magic:
%%writefile mod.py
def f(x):
return 1.0/(x-1)
def g(y):
return f(y+1)
Writing mod.py
Now let's call the function g
with an argument that would produce an error:
import mod
mod.g(0)
--------------------------------------------------------------------------- ZeroDivisionError Traceback (most recent call last) <ipython-input-34-a54c5799f57e> in <module>() 1 import mod ----> 2 mod.g(0) /home/fperez/teach/astro-hack-week/day1/ipython/mod.py in g(y) 4 5 def g(y): ----> 6 return f(y+1) /home/fperez/teach/astro-hack-week/day1/ipython/mod.py in f(x) 1 2 def f(x): ----> 3 return 1.0/(x-1) 4 5 def g(y): ZeroDivisionError: float division by zero
Since 1.0 the IPython notebook web application support raw_input
which for example allow us to invoke the %debug
magic in the notebook:
mod.g(0)
--------------------------------------------------------------------------- ZeroDivisionError Traceback (most recent call last) <ipython-input-40-5e708f13c839> in <module>() ----> 1 mod.g(0) /home/fperez/teach/astro-hack-week/day1/ipython/mod.py in g(y) 4 5 def g(y): ----> 6 return f(y+1) /home/fperez/teach/astro-hack-week/day1/ipython/mod.py in f(x) 1 2 def f(x): ----> 3 return 1.0/(x-1) 4 5 def g(y): ZeroDivisionError: float division by zero
%debug
> /home/fperez/teach/astro-hack-week/day1/ipython/mod.py(3)f() 2 def f(x): ----> 3 return 1.0/(x-1) 4 ipdb> u > /home/fperez/teach/astro-hack-week/day1/ipython/mod.py(6)g() 4 5 def g(y): ----> 6 return f(y+1) ipdb> q
Don't foget to exit your debugging session. Raw input can of course be use to ask for user input:
enjoy = raw_input('Are you enjoying this tutorial ?')
print 'enjoy is :', enjoy
Are you enjoying this tutorial ?Yes ! enjoy is : Yes !
%%
magics¶%%perl
@months = ("July", "August", "September");
print $months[0];
July
%%ruby
name = "world"
puts "Hello #{name.capitalize}!"
Hello World!
%connect_info
{ "stdin_port": 50023, "ip": "127.0.0.1", "control_port": 50024, "hb_port": 50025, "signature_scheme": "hmac-sha256", "key": "b54b8859-d64d-48bb-814a-909f9beb3316", "shell_port": 50021, "transport": "tcp", "iopub_port": 50022 } Paste the above JSON into a file, and connect with: $> ipython <app> --existing <file> or, if you are local, you can connect with just: $> ipython <app> --existing kernel-30f00f4a-230c-4e64-bea5-0e5f6a52cb40.json or even just: $> ipython <app> --existing if this is the most recent IPython session you have started.
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:
%qtconsole