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Reference Docs

for standard objects and modules, see Python Standard Library
for language reference, see Python Language Reference

Index

Unix Script

on top of the file, add

#!/usr/bin/env python3.1

Encoding type

on top of the file, add

# -*- coding: encoding -*-

Looping Techniques

items() for dict

>>> knights = {'gallahad': 'the pure', 'robin': 'the brave'}
>>> for k, v in knights.items():
...     print(k, v)
...
gallahad the pure
robin the brave

enumerate() for sequence

>>> for i, v in enumerate(['tic', 'tac', 'toe']):
...     print(i, v)
...
0 tic
1 tac
2 toe

zip() for two or more sequences at the same time

>>> questions = ['name', 'quest', 'favorite color']
>>> answers = ['lancelot', 'the holy grail', 'blue']
>>> for q, a in zip(questions, answers):
...     print('What is your {0}?  It is {1}.'.format(q, a))
...
What is your name?  It is lancelot.
What is your quest?  It is the holy grail.
What is your favorite color?  It is blue.

To loop over a sequence in reverse, first specify the sequence in a forward direction and then call the reversed() function

>>> for i in reversed(range(1, 10, 2)):
...     print(i)
...
9
7
5
3
1

sorted() for sorting while leaving the source unaltered

>>> basket = ['apple', 'orange', 'apple', 'pear', 'orange', 'banana']
>>> for f in sorted(set(basket)):
...     print(f)
...
apple
banana
orange
pear

to change a list while you are looping over it; however, it is often simpler and safer to create a new list instead

>>> import math
>>> raw_data = [56.2, float('NaN'), 51.7, 55.3, 52.5, float('NaN'), 47.8]
>>> filtered_data = []
>>> for value in raw_data:
...     if not math.isnan(value):
...         filtered_data.append(value)
...
>>> filtered_data
[56.2, 51.7, 55.3, 52.5, 47.8]

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