它是pythonic:命名lambdas [英] Is it pythonic: naming lambdas

问题描述

我开始欣赏lambda表达式在python中的价值，尤其是在函数式编程中，map， functions返回函数，等等.但是，我也一直在函数中命名lambda，因为:

I'm beginning to appreciate the value of lambda expressions in python, particularly when it comes to functional programming, map, functions returning functions, etc. However, I've also been naming lambdas within functions because:

• 我多次需要相同的功能，并且不想重复代码.
• 该功能特定于其出现的功能；它不需要其他地方.

当遇到满足上述条件的情况时，我一直在编写一个命名的lambda表达式，以便进行DRY并缩小作用域的范围.例如，我正在编写一个在某些numpy数组上运行的函数，并且我需要对传递给该函数的所有数组进行适度繁琐的索引编制(可以很容易地放在一行上).我已经编写了一个名为lambda表达式来进行索引编制，而不是编写整个其他函数或在整个函数定义中多次复制/粘贴索引.

When I encounter a situation that meets the above criteria, I've been writing a named lambda expression in order to DRY and narrowly scope functionality. For example, I am writing a function that operates on some numpy arrays, and I need to do some moderately tedious indexing of all the arrays passed to the function (which can easily fit on a single line). I've written a named lambda expression to do the indexing instead of writing a whole other function or copy/pasting the indexing several times throughout the function definition.

def fcn_operating_on_arrays(array0, array1):
    indexer = lambda a0, a1, idx: a0[idx] + a1[idx]

    # codecodecode

    indexed = indexer(array0, array1, indices)

    # codecodecode in which other arrays are created and require `indexer`

    return the_answer

这是否滥用python的lambda?我应该吸收它并定义一个单独的功能吗?

Is this an abuse of python's lambdas? Should I just suck it up and define a separate function?

可能值得链接函数内部的函数.

推荐答案

这不是Pythonic， PEP8不建议使用:

This is not Pythonic and PEP8 discourages it:

始终使用def语句而不是使用赋值语句 直接将lambda表达式绑定到标识符.

Always use a def statement instead of an assignment statement that binds a lambda expression directly to an identifier.

是:

def f(x): return 2*x

否:

f = lambda x: 2*x

第一种形式表示结果函数对象的名称为 特别是'f'而不是通用'<lambda>'.这更多 通常对于回溯和字符串表示很有用.使用 赋值语句的注释消除了lambda的唯一好处 表达式可以提供显式的def语句(即它可以 嵌入更大的表达式中

The first form means that the name of the resulting function object is specifically 'f' instead of the generic '<lambda>'. This is more useful for tracebacks and string representations in general. The use of the assignment statement eliminates the sole benefit a lambda expression can offer over an explicit def statement (i.e. that it can be embedded inside a larger expression)

经验法则是考虑其定义 :lambdas表达式是匿名函数.如果您命名，它就不再是匿名的了. :)

A rule of thumb for this is to think on its definition: lambdas expressions are anonymous functions. If you name it, it isn't anonymous anymore. :)

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