flatten 展平列表操作

maiyantao

py 中有时候需要展平一个嵌套的列表，偶然发现一个已经实现的工具，位于：parlse.utils.py

1. from typing import Any, Iterable, Iterator, List
   
2. 
   
3. 
   
4. def flatten(x: Iterable[Any]) -> List[Any]:
   
5.     """flatten(sequence) -> list
   
6.     Returns a single, flat list which contains all elements retrieved
   
7.     from the sequence and all recursively contained sub-sequences
   
8.     (iterables).
   
9.     Examples:
   
10.     >>> [1, 2, [3,4], (5,6)]
    
11.     [1, 2, [3, 4], (5, 6)]
    
12.     >>> flatten([[[1,2,3], (42,None)], [4,5], [6], 7, (8,9,10)])
    
13.     [1, 2, 3, 42, None, 4, 5, 6, 7, 8, 9, 10]
    
14.     >>> flatten(["foo", "bar"])
    
15.     ['foo', 'bar']
    
16.     >>> flatten(["foo", ["baz", 42], "bar"])
    
17.     ['foo', 'baz', 42, 'bar']
    
18.     """
    
19.     return list(iflatten(x))
    
20. 
    
21. 
    
22. def iflatten(x: Iterable[Any]) -> Iterator[Any]:
    
23.     """iflatten(sequence) -> Iterator
    
24.     Similar to ``.flatten()``, but returns iterator instead"""
    
25.     for el in x:
    
26.         if _is_listlike(el):
    
27.             yield from flatten(el)
    
28.         else:
    
29.             yield el
    
30. 
    
31. 
    
32. def _is_listlike(x: Any) -> bool:
    
33.     """
    
34.     >>> _is_listlike("foo")
    
35.     False
    
36.     >>> _is_listlike(5)
    
37.     False
    
38.     >>> _is_listlike(b"foo")
    
39.     False
    
40.     >>> _is_listlike([b"foo"])
    
41.     True
    
42.     >>> _is_listlike((b"foo",))
    
43.     True
    
44.     >>> _is_listlike({})
    
45.     True
    
46.     >>> _is_listlike(set())
    
47.     True
    
48.     >>> _is_listlike((x for x in range(3)))
    
49.     True
    
50.     >>> _is_listlike(range(5))
    
51.     True
    
52.     """
    
53.     return hasattr(x, "__iter__") and not isinstance(x, (str, bytes))
    
54. 
    
55. 
    
56. if __name__ == '__main__':
    
57.     print(flatten([[[1, 2, 3, [7, 8]], (42, None)], [4, 5], [6], 7, (8, 9, 10)]))
    

复制代码