Python notes, python

Python notes, python

This article is a supplement to the Python notes -- decorator.

When using the decorator, some attributes of the decorated function will be lost, such as the following code:

 1 #!/usr/bin/env python 2  3 def deco(func): 4     def wrapper(): 5         print "Wrap start" 6         func() 7         print "Wrap end\n" 8     return wrapper 9 10 @deco11 def foo():12     """Docstring for foo"""13     print "In foo():"14 15 foo()16 print foo.__name__17 print foo.__doc__

The output is as follows:

$ python decorator_test.pyWrap startIn foo():Wrap endwrapperNone

We can see that the __name _ attribute is wrapper, while the _ doc _ attribute is None. This is inconvenient for common use. You cannot rewrite _ name _ and _ doc _ for every function using the decorator.

The update_wrapper and wraps provided by Python functools can effectively solve this problem. However, update_wrapper is called in the form of a method, while wraps encapsulates update_wrapper with a decorator. The sample code is as follows:

1 #! /Usr/bin/env python 2 from functools import update_wrapper 3 4 def deco (func): 5 def wrapper (): 6 print "Wrap start" 7 func () 8 print "Wrap end \ n" 9 return update_wrapper (wrapper, func) # Call the update_wrapper Method 10 11 @ deco12 def foo (): 13 "Docstring for foo" 14 print "In foo ():" 15 16 foo () 17 print foo. _ name _ 18 print foo. _ doc __

1 #! /Usr/bin/env python 2 from functools import wraps 3 4 def deco (func): 5 @ wraps (func) # Use the decorator to implement 6 def wrapper (): 7 print "Wrap start" 8 func () 9 print "Wrap end \ n" 10 return wrapper11 12 @ deco13 def foo (): 14 "Docstring for foo" 15 print "In foo ():" 16 17 foo () 18 print foo. _ name _ 19 print foo. _ doc __

The foo method decorated by deco can retain the previous _ name _ and _ doc _ attributes.

$ python decorator_test_with_update_wrapper.pyWrap startIn foo():Wrap endfooDocstring for foo$ python decorator_test_with_wraps.pyWrap startIn foo():Wrap endfooDocstring for foo

 

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1. CPU (no matter what, including the mobile phone's ARM chip)
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