Some special uses of Python Python (map, reduce, filter, lambda, list derivation, etc.) __python

map function:

Prototype: Map (function, sequence), which is to map a list to another list,

How to use:

def f (x):

Return x**2

L = Range (1,10)

Map (f,l)

OUT[3]: [1, 4, 9, +, BA] reduce function

Prototypes: Reduce (function, sequence, startvalue), which is to generalize a list into one output,
How to use:

def f2 (x,y):

Return X+y

Reduce (f1,l)

OUT[7]: 45

Reduce (f2,l,10)

OUT[8]: The filter function

Prototype: filter (function, sequence) that filters out some elements of a list according to the function defined.
How to use:

def f2 (x):

return x%2!= 0

Filter (F2,L)

OUT[5]: [1, 3, 5, 7, 9]

Remember: The function here must return a Boolean value. Lambda functions

Prototypes: Lambda < parameters: function body, implicit function, define some simple operations,
How to use:

F3 = Lambda x:x**2

F3 (2)

OUT[10]: 4

You can also combine map, reduce, and filter to use, such as:

Map (f3,l)

OUT[11]: [1, 4, 9, +, BA] list of deduced

Basic form: [X for item in sequence <if (conditions)], where x represents the operation of the item,

How to use:

[I**2 for I in L]

OUT[12]: [1, 4, 9, +, BA] dictionary set default values

The default value of setting entries in the Python dictionary is sometimes useful, such as initializing a dictionary.
How to use:

x = {}

X.setdefault (1,0)

OUT[15]: 0

X[2] = 10

X

OUT[17]: {1:0, 2:10}

X.setdefault (2,1)

OUT[18]: 10

Author: Alex Yu
Source: http://www.cnblogs.com/biaoyu/
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