哪个更可取:lambda 函数或嵌套函数 ('def')? [英] Which is more preferable to use: lambda functions or nested functions ('def')?

问题描述

我主要使用 lambda 函数，但有时使用似乎提供相同行为的嵌套函数.

这里有一些简单的例子，如果在另一个函数中找到它们，它们在功能上做同样的事情:

Lambda 函数

<预><代码>>>>a = λ x : 1 + x>>>一(5)6

嵌套函数

<预><代码>>>>def b(x): 返回 1 + x>>>乙(5)6

使用一种比另一种有优势吗?(性能?可读性?限制?一致性?等)

这还重要吗?如果没有，那么这是否违反了 Pythonic 原则:

<块引用>

应该有一个——最好只有一个——明显的方法..

解决方案

如果您需要将 lambda 分配给名称，请改用 def.def 只是赋值的语法糖，所以结果是一样的，而且它们更加灵活和可读.

lambdas 可以用于使用一次，扔掉没有名字的函数.

然而，这种用例非常罕见.您很少需要传递未命名的函数对象.

内置map() 和filter() 需要函数对象，但列表推导式 和生成器表达式通常比那些函数更具可读性，并且可以涵盖所有用例，而无需 lambda.

如果你真的需要一个小函数对象，你应该使用operator模块函数，比如operator.add而不是lambda x,y:x + y

如果您仍然需要一些未涵盖的 lambda，您可以考虑编写一个 def，以提高可读性.如果函数比 operator 模块中的函数更复杂，def 可能更好.

因此，现实世界中好的 lambda 用例非常罕见.

I mostly use lambda functions but sometimes use nested functions that seem to provide the same behavior.

Here are some trivial examples where they functionally do the same thing if either were found within another function:

Lambda function

>>> a = lambda x : 1 + x
>>> a(5)
6

Nested function

>>> def b(x): return 1 + x

>>> b(5)
6

Are there advantages to using one over the other? (Performance? Readability? Limitations? Consistency? etc.)

Does it even matter? If it doesn't then does that violate the Pythonic principle:

There should be one-- and preferably only one --obvious way to do it..

解决方案

If you need to assign the lambda to a name, use a def instead. defs are just syntactic sugar for an assignment, so the result is the same, and they are a lot more flexible and readable.

lambdas can be used for use once, throw away functions which won't have a name.

However, this use case is very rare. You rarely need to pass around unnamed function objects.

The builtins map() and filter() need function objects, but list comprehensions and generator expressions are generally more readable than those functions and can cover all use cases, without the need of lambdas.

For the cases you really need a small function object, you should use the operator module functions, like operator.add instead of lambda x, y: x + y

If you still need some lambda not covered, you might consider writing a def, just to be more readable. If the function is more complex than the ones at operator module, a def is probably better.

So, real world good lambda use cases are very rare.

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