Question

我有这样的python代码：

newlist =[[52, None, None], [129, None, None], [56, None, None], [111, None, None],  
          [22, None, None], [33, None, None], [28, None, None], [52, None, None],  
          [52, None, None], [52, None, None], [129, None, None], [56, None, None],  
          [111, None, None], [22, None, None], [33, None, None], [28, None, None]]

我希望newlist喜欢：

newlist =[52, None, None,129, None, None,56, None, None,111, None, None,22, 
          None, None,33, None, None,28, None, None,52, None, None,52, None,  
          None,52, None, None,129, None, None,56, None, None, 111, None,  
          None,22, None, None,33, None, None,28, None, None]

有什么方法可以解决吗？

Answer 1

您要做的事情称为展平列表。根据{{3}}，你正在努力做正确的事。引用那个

Flat比嵌套好。

所以你可以像这样使用列表理解

newlist = [item for items in newlist for item in items]

或者您可以使用chain中的itertools

from itertools import chain
newlist = list(chain(*newlist))

或者您可以使用chain.from_iterable，其中无需解压缩列表

from itertools import chain
newlist = list(chain.from_iterable(newlist))

使用sum功能
```
newlist = sum(newlist, [])
```

使用reduce功能

newlist = reduce(lambda x,y: x+y, newlist)

使用operator.add。这比reduce版lambda更快。

import operator
newlist = reduce(operator.add, newlist)

修改：为了完整起见，还包括Zen of Python中的答案。

我尝试在 Python 2.7 中计算所有这些内容，就像这样

from timeit import timeit
print(timeit("[item for items in newlist for item in items]", "from __main__ import newlist"))
print(timeit("sum(newlist, [])", "from __main__ import newlist"))
print(timeit("reduce(lambda x,y: x+y, newlist)", "from __main__ import newlist"))
print(timeit("reduce(add, newlist)", "from __main__ import newlist; from operator import add"))
print(timeit("list(chain(*newlist))", "from __main__ import newlist; from itertools import chain"))
print(timeit("list(chain.from_iterable(newlist))", "from __main__ import newlist; from itertools import chain"))

我机器上的输出

2.26074504852
2.45047688484
3.50180387497
2.56596302986
1.78825688362
1.61612296104

因此，最有效的方法是在Python 2.7中使用list(chain.from_iterable(newlist))。在 Python 3.3

from timeit import timeit
print(timeit("[item for items in newlist for item in items]", "from __main__ import newlist"))
print(timeit("sum(newlist, [])", "from __main__ import newlist"))
print(timeit("reduce(lambda x,y: x+y, newlist)", "from __main__ import newlist; from functools import reduce"))
print(timeit("reduce(add, newlist)", "from __main__ import newlist; from operator import add; from functools import reduce"))
print(timeit("list(chain(*newlist))", "from __main__ import newlist; from itertools import chain"))
print(timeit("list(chain.from_iterable(newlist))", "from __main__ import newlist; from itertools import chain"))

我机器上的输出

2.26074504852
2.45047688484
3.50180387497
2.56596302986
1.78825688362
1.61612296104

因此，无论是Python 2.7还是3.3，使用list(chain.from_iterable(newlist))来展平嵌套列表。

Answer 2

temp = []
for small_list in newlist:
    temp += small_list
newlist = temp

这应该这样做。

Answer 3

尝试：

newlist = [j for i in newlist for j in i]

Answer 4

最简单的一个：

newlist = sum(newlist, [])
print newlist

如何展平列表/嵌套列表列表？

4 个答案: