Python 实现 first()

zltzlt

Python 实现 first()

上代码：

1. _def = object()    # default value
   
2. 
   
3. 
   
4. def first(iterable, *, default=_def):
   
5.     """first(iterable, *, default) --> The first item of *iterable*, or *default* if *iterable* is empty"""
   
6.     for i in iterable:
   
7.         return i
   
8.     if default is _def:    # no default value was provided
   
9.         raise ValueError('first() was called on an empty iterable, and no default value was provided.')
   
10.     return default
    
11. 
    
12. 
    
13. print(first([3, 4, 6, 7]))     # Out 3
    
14. print(first(range(5, 8)))      # Out 5
    
15. print(first([], default=0))    # Out 0
    
16. print(first(()))               # Error

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如果代码有问题，欢迎在评论区指正

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