Python 将函数应用于列表的每个元素
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Apply function to each element of a list
提问by shantanuo
How do I apply a function to the list of variable inputs?
For e.g. the filterfunction returns true values but not the actual output of the function.
如何将函数应用于变量输入列表？例如，filter函数返回真值而不是函数的实际输出。
from string import upper
mylis=['this is test', 'another test']
filter(upper, mylis)
['this is test', 'another test']
The expected output is :
预期的输出是：
['THIS IS TEST', 'ANOTHER TEST']
I know upperis built-in. This is just an example.
我知道upper是内置的。这只是一个例子。
采纳答案by mdml
I think you mean to use mapinstead of filter:
>>> from string import upper
>>> mylis=['this is test', 'another test']
>>> map(upper, mylis)
['THIS IS TEST', 'ANOTHER TEST']
Even simpler, you could use str.upperinstead of importing from string(thanks to @alecxe):
更简单的是，您可以使用str.upper而不是从导入string（感谢@alecxe）：
>>> map(str.upper, mylis)
['THIS IS TEST', 'ANOTHER TEST']
In Python 2.x, mapconstructs a new list by applying a given function to every element in a list. filterconstructs a new list by restricting to elements that evaluate to Truewith a given function.
在 Python 2.x 中，map通过将给定函数应用于列表中的每个元素来构造一个新列表。filter通过限制对True给定函数求值的元素来构造一个新列表。
In Python 3.x, mapand filterconstruct iterators instead of lists, so if you are using Python 3.x and require a list the list comprehension approach would be better suited.
在Python 3.x中，map和filter构建迭代器，而非列表，所以如果你使用Python 3.x和要求的清单列表解析的方法会更适合。
回答by alecxe
Or, alternatively, you can take a list comprehensionapproach:
或者，您可以采取一种list comprehension方法：
>>> mylis = ['this is test', 'another test']
>>> [item.upper() for item in mylis]
['THIS IS TEST', 'ANOTHER TEST']
