python - 在 reduce 函数中传递两个以上的参数

Question

我知道 Python reduce 只接受带有两个参数的函数。但是，有没有办法使函数可以使用两个以上的参数？我不想让它成为一个全局变量，因为它对所有其他导入都是可见的。以下片段可能有助于描述问题(请阅读片段中的评论):

# The reduce function
def apply_something(something, config):
    # Consrtuct a class object based on the truth value of some other variable.
    # some_var can be changed and is being accessed in different threads so its 
    # not safe to make it global. The reduce function is being called from 
    # inside some other function so It would be better to make 
    # some_var only accessible in the function context.

    if some_var:
        obj = Klass(some_var)
    else:
        obj = Klass()

def callee():
    # This is how I apply the reduce operation.
    reduce(apply_something, [1, 2, 3], something_initializer)

    # I want something like this:
    some_var = True  # So this can be accessed in apply_something

请提供对此类问题的一些见解。

Answer 1

我想你要找的是 partial function application ，您可以使用 functools 来做到这一点.

def apply_something(something, config, some_var):
    pass  # ...

import functools

functools.reduce(functools.partial(apply_something, some_var=True), 
       [1, 2, 3], something_initializer)

例子:

>>> def foo(a, b, c):
...     return a + b if c else a * b

>>> functools.reduce(functools.partial(foo, c=True), [1,2,3,4,5], 0)
15

>>> functools.reduce(functools.partial(foo, c=False), [1,2,3,4,5], 1)
120