Видео надо смотреть с 25-ой минуты (IPython in Depth, SciPy2013 Tutorial, Part 1 of 3 )... Как получать помощь (? ?? %quickref ...), история , i, _7, %history -n 1-5, files=!ls, !echo
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.
First things first: running code, getting help¶
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-Enterto force the creation of a new cell unconditionally (useful when inserting new content in the middle of an existing notebook).Control-Enterexecutes 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¶
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.
The interactive workflow: input, output, history¶
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2+10
Out[7]:
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_+10
Out[8]:
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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_
Out[10]:
The output is stored in
_N and Out[N] variables:
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_7 == Out[7]
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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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In[11]
Out[13]:
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_i
Out[14]:
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_ii
Out[15]:
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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
Write the last 10 lines of history to a file named
log.py.Accessing the underlying operating system¶
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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()}
Beyond Python: magic functions¶
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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Running normal Python code: execution and errors¶
Notonly 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)
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%xmode plain
mod.g(0)
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%xmode verbose
mod.g(0)
The default
%xmode is "context", which shows additional context but not all local variables. Let's restore that one for the rest of our session.
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%xmode context
Raw Input in the notebook¶
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
Plotting in the notebook¶
This imports numpy as
np and matplotlib's plotting routines as plt, plus setting lots of other stuff for you to work interactivel very easily:
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%matplotlib inline
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import numpy as np
import matplotlib.pyplot as plt
from matplotlib.pyplot import gcf
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x = np.linspace(0, 2*np.pi, 300)
y = np.sin(x**2)
plt.plot(x, y)
plt.title("A little chirp")
f = gcf() # let's keep the figure object around for later...
The IPython kernel/client model¶
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%connect_info
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%qtconsole
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