Python Filter,map,lambda,reduce, List parsing

Filter usage filter (FUNC,SEQ)

Converts the elements of a SEQ into Func by one generation, using the return value of Func to determine whether to retain or filter

1 def foo (x): 2     return x>334 >>> filter (Foo,range (6))5 [4, 5]

>>> Filter (lambda x:x>3,range (6))
[4, 5]

6 # Note that you only need to write the function name without parameters

Map usage map (FUNC/LAMBDA,SEQ)

By using a function to manipulate each element in the queue, the element is replaced with a return value, note that a new sequence is generated and the original sequence does not change

>>> map (Lambda x:x*2,range (62, 4, 6, 8, ten# the same, here is either a lambda expression, Or is it a function name >>> a[1, 2, 3, 4, 5, 6]>>> Map (foo,a) [False, False, False, True, Tr UE, True]>>> a[1, 2, 3, 4, 5, 6]#foo is to determine if X is greater than three, is true, no returns false
Operations on multiple sequences

>>> map(Lambda X,y:x+y,range (4), Range (5))

Traceback (most recent):
File "<pyshell#84>", line 1, in <module>
Map (Lambda X,y:x+y,range (4), Range (5))
File "<pyshell#84>", line 1, in <lambda>
Map (Lambda X,y:x+y,range (4), Range (5))
typeerror:unsupported operand type (s) for +: ' Nonetype ' and ' int '
>>> map(Lambda X,y:x+y,range (4), Range (4))
[0, 2, 4, 6]

List parsing

[Expression/function, for loop]

>>> [x**2 forXinchRange (6)][0,1, 4, 9, 16, 25]>>> [a**2 forXinchRange (6)][1, 1, 1, 1, 1, 1]>>>#It can be seen that when you write an unrelated variable in a for loop, it simply repeats the result of the expression>>> [foo (x) forXinchRange (6)][false, False, False, False, True, True]#here's the function with parentheses, Foo ibid .>>> [LambdaX:x**2 forXinchRange (6)][<function <Lambda> at 0x01de8870>, <function <Lambda> at 0x01de8830>, <function <Lambda> at 0x01de88f0>, <function <Lambda> at 0x01de8930>, <function <Lambda> at 0x01de8970>, <function <Lambda> at 0x01de89b0>]>>> [(Lambdax:x**2) (x) forXinchRange (6)][0,1, 4, 9, 16, 25]#also you need to think of lambda as a function name, or a return value>>> [x**2 forXinchRange (6)ifX**2>9][16, 25]>>> [(X**2,Y**3) forXinchRange (4) forYinchRange (3)ifX>0 andY>0] [(1, 1), (1, 8), (4, 1), (4, 8), (9, 1), (9, 8)]>>>#consider the subsequent for as nested, and the preceding expression remember parentheses

Reduce iterates over the item order in sequence call function, and if there is starting_value, it can also be called as an initial value

>>> reduce (lambda x,y:x+y,range (1,101))#reduce must accept a two-dollar function, such as above (((1+2) + 3) +4) + ... >>> reduce (lambda x,y:x+y,range (1,101), 5150# ) accepted initial value

Python Filter,map,lambda,reduce, List parsing