带有3个输入的python 3 map/lambda方法 [英] python 3 map/lambda method with 2 inputs

问题描述

我在python 3中有如下字典:

I have a dictionary like the following in python 3:

ss = {'a':'2', 'b','3'}

我想使用map函数将他的所有值转换为int，我写了这样的东西:

I want to convert all he values to int using map function, and I wrote something like this:

list(map(lambda key,val: int(val), ss.items())))

但是python抱怨:

but the python complains:

TypeError:()缺少1个必需的位置参数:'val'

TypeError: () missing 1 required positional argument: 'val'

我的问题是如何编写具有两个输入(例如key和val)的lambda函数

My question is how can I write a lambda function with two inputs (E.g. key and val)

推荐答案

ss.items()将给出一个可迭代的对象，该对象将在每次迭代时提供元组.在lambda函数中，已将其定义为接受两个参数，但是元组将被视为单个参数.因此，没有值可以传递给第二个参数.

ss.items() will give an iterable, which gives tuples on every iteration. In your lambda function, you have defined it to accept two parameters, but the tuple will be treated as a single argument. So there is no value to be passed to the second parameter.

1. 您可以像这样修复它

1. You can fix it like this

print(list(map(lambda args: int(args[1]), ss.items())))
# [3, 2]

如果仍然忽略键，只需使用ss.values()这样

print(list(map(int, ss.values())))
# [3, 2]

否则，按照Ashwini的建议， Chaudhary ，使用 itertools.starmap ，

Otherwise, as suggested by Ashwini Chaudhary, using itertools.starmap,

from itertools import starmap
print(list(starmap(lambda key, value: int(value), ss.items())))
# [3, 2]

我更喜欢列表理解方式

I would prefer the List comprehension way

print([int(value) for value in ss.values()])
# [3, 2]

在Python 2.x中，您可以这样做

In Python 2.x, you could have done that like this

print map(lambda (key, value): int(value), ss.items())

此功能称为元组参数解包.但这已在Python 3.x中删除.在 PEP-3113

This feature is called Tuple parameter unpacking. But this is removed in Python 3.x. Read more about it in PEP-3113

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