Smooth python and cookbook learning notes (8), pythoncookbook

Smooth python and cookbook learning notes (8), pythoncookbook
1. The default parameters of the function must be unchangeable.

If the default parameter of a function is a variable object, modification of the default parameter outside the function will also affect the function itself.

>>> Def spam (a, B = None): # variable parameters such as empty list [] cannot be used if B is an unchangeable parameter... if B is None :... B = []...

 

2. Anonymous Functions

1. You can use an anonymous function if you do not know the function name or want a short operation.

>>> Sum = lambda x, y: x + y >>>> sum (2, 3) 5 >>> def sum (x, y): # The above anonymous function, equivalent to this function... print (x + y)... >>> sum (3, 4) 7

2. bind variables to anonymous Functions

>>> X = 10 >>> a = lambda y: x + y >>>> x = 20 >>> B = lambda y: x + y> a (5) # found that not the expected 15, because x is changed by 25 >>> B (5) 25 >>> x = 25 >>> a = lambda y, x = x: x + y # bind x when defining, x is a local variable, not Affected by x changes> B = lambda y, x = x: x + y> a (5) 30> B (5) 20