Filter, Map & Reduce of list

将开发过程中经常用到的内容备份一下，下面的代码段是关于Filter, Map & Reduce of lists的代码。

# [SNIPPET_NAME: Filter, Map & Reduce of lists]

# [SNIPPET_CATEGORIES: Python Core]

# [SNIPPET_DESCRIPTION: Simple examples to show common features in everyday work with lists]

# [SNIPPET_AUTHOR: Benjamin Klueglein <scheibenkaes@googlemail.com>]

# [SNIPPET_LICENSE: GPL]

numbers = range(1, 20, 1) # Numbers from 1 to 20

#########################

# Filtering of lists:

# Pick a amount of items which match a certain condition

#########################

# e.g. Get all odd numbers

odd_numbers = filter(lambda n: n % 2, numbers)

print odd_numbers

# prints [1, 3, 5, 7, 9, 11, 13, 15, 17, 19]

#########################

#########################

# Mapping of lists:

# Apply a function to each item and return the result of each invocation in a list

#########################

# Calculate the square of two for each number

# Alternate approach:

print squared_numbers

# prints [1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 144, 169, 196, 225, 256, 289, 324, 361]

#########################

#########################

# Reducing of lists

# Apply a function of two arguments cumulatively to the items of a sequence,

#    from left to right, so as to reduce the sequence to a single value.

# (Taken from reduce docstring)

#########################

# Sum up all numbers

sum_of_numbers = reduce(lambda n, m: n + m, numbers)

print sum_of_numbers

# prints 190

#########################