更短的"lambda"关键字替代方法?

问题描述：

Python是关于简单易读的代码的.它的版本比以前更好，我是忠实的粉丝！但是，每次必须定义lambda时键入l a m b d a都是不好玩的(您可能会不同意). 问题是，这6个字符l a m b d a使我的语句更长，特别是当我在map和filter s中嵌套几个lambda时. 我嵌套的数量不超过2或3，因为它占用了python的可读性！

Python is about simple and readable code. It got better over the versions and I am a huge fan! However, typing l a m b d a every time I have to define a lambda is not fun (you may disagree). The problem is, these 6 characters l a m b d a make my statements longer, especially when I nest a couple of lambdas inside maps and filters. I am not nesting more than 2 or three, because it takes away the readability of python!

# How to rename/alias a keyword to a nicer one? 
lines = map(lmd x: x.strip(), sys.stdin)

# OR, better yet, how to define my own operator like -> in python?
lines = map(x -> x.strip(), sys.stdin)
# Or may be :: operator is pythonic
lines = map(x :: x.strip(), sys.stdin)

# INSTEAD of this ugly one. Taking out this is my goal!
lines = map(lambda x: x.strip(), sys.stdin)

我很高兴添加这样的导入:

I am happy to add import like this:

from myfuture import lmd_as_lambda
# OR
from myfuture import lambda_operator

答

好消息是:您根本不需要使用map或filter，您可以使用列表理解(急切)，因此完全避免了lambda.

The good news is: You don't need to use map or filter at all, you can use generator expressions (lazy) or list comprehensions (eager) instead and thus avoid lambdas completely.

所以代替:

lines = map(lambda x: x.strip(), sys.stdin)

只需使用:

# You can use either of those in Python 2 and 3, but map has changed between
# Python 2 and Python 3 so I'll present both equivalents:
lines = (x.strip() for x in sys.stdin)  # generator expression (Python 3 map equivalent)
lines = [x.strip() for x in sys.stdin]  # list comprehension   (Python 2 map equivalent)

如果您使用理解力，它可能也会更快.在map或filter中使用时，实际上很少有函数会更快-使用lambda时，会有更多的反模式(而且很慢).

It's probably also faster if you use comprehensions. Very few functions are actually faster when used in map or filter - and using a lambda there is more of an anti-pattern (and slow).

该问题仅包含map的示例，但是您也可以替换filter.例如，如果您要filter排除奇数:

The question only contained an example for map, but you can also replace filter. For example if you want to filter out odd numbers:

filter(lambda x: x%2==0, whatever)

您可以改为使用条件理解:

You can use a conditional comprehension instead:

(x for x in whatever if x%2==0)
[x for x in whatever if x%2==0]

您甚至可以将map和filter组合在一起:

You could even combine a map and filter in one comprehension:

(x*2 for x in whatever if x%2==0)

只需考虑map和filter的外观:

map(lambda x: x*2, filter(lambda x: x%2==0, whatever))

注意:这并不意味着lambda没有用！在很多地方lambda非常方便.考虑sorted 的 key参数(对于min同样和max)或 functools.reduce (但最好远离该函数，大多数情况下通常需要一个谓词函数的for -loop或itertools可读性更好: ， itertools.groupby 和

Note: That doesn't mean lambda isn't useful! There are lots of places where lambdas are very handy. Consider the key argument for sorted (and likewise for min and max) or functools.reduce (but better keep away from that function, most of the times a normal for-loop is more readable) or itertools that require a predicate function: itertools.accumulate, itertools.dropwhile, itertools.groupby and itertools.takewhile. Just to name a few examples where a lambda could be useful, there are probably lots of other places as well.

更短的"lambda"关键字替代方法?

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