Python Special Syntax: filter, map, reduce, lambda

Python has built-in special functions that are Python-specific. You can make your code more concise.

Examples can be seen:

1 filter (function, sequence):

str = [' A ', ' B ', ' C ', ' d ']

def fun1 (s): return s if s! = ' a ' else None

RET = filter (FUN1, str)

Print ret

# # [' B ', ' C ', ' d ']

A function (item) is executed on item in sequence, and the item that executes the result of true consists of a list/string/tuple (depending on the type of sequence) returned.

Can be seen as a filter function.

2 map (function, sequence)

str = [' A ', ' B ', ' C ', ' d ']

def fun2 (s): return S + ". txt"

ret = map (fun2, str)

Print ret

# # [' A.txt ', ' b.txt ', ' c.txt ', ' d.txt ']

Execute function (item) on item in sequence, and see the result of the execution to make a list return:

Map also supports multiple sequence, which requires that the function also supports the corresponding number of parameter inputs:
def add (x, y): Return x+y
Print map (add, Range), range (10))
##[0, 2, 4, 6, 8, 10, 12, 14, 16, 18]

3 reduce (function, sequence, Starting_value): def add1 (x, y): return x + y

Print reduce (ADD1, range (1, 100))

Print reduce (ADD1, range (1, 100), 20)

# 4950 (Note: 1+2+...+99)
# 4970 (Note: 1+2+...+99+20)

The function is called on an iteration of the item order in sequence, and if there is starting_value, it can also be called as an initial value, for example to sum the list:

4 Lambda:

g = lambda s:s + ". FSH"

Print g ("haha")

Print (Lambda x:x * 2) (3)

# # HAHA.FSH

# 6

This is an interesting syntax that Python supports, which allows you to quickly define the smallest function of a single line, similar to a macro in C, which are called lambda functions.

Python Special Syntax: filter, map, reduce, lambda