如何通过引用调用多个Python函数来操作一个变量，以便轻松更改函数调用的顺序？

Question

我想创建一个“功能管道”，就像工厂一样。

假设我有以下功能：

def func1(var):
    var = # do something with var
    return var

def func2(var):
    var = # do something else with var
    return var

def func3(var):
    var = # do another thing with var
    return var

def func4(var):
    var = # do something with var we haven't done before
    return var

现在我想按顺序调用对象上的所有函数，但我想测试以所有可能的顺序排列调用它们并检查结果，因为最终结果将根据调用函数的顺序而变化。

如何更改此手动函数调用顺序：

myvar = something
myvar = func1(myvar)
myvar = func2(myvar)
myvar = func3(myvar)
myvar = func4(myvar) # final variable function transformation (result)

...我可以迭代所有可能的序列，但无需按如下方式手动编码？

def func1(var):
    var = # do something with var
    return var

def func2(var):
    var = # do something else with var
    return var

def func3(var):
    var = # do another thing with var
    return var

def func4(var):
    var = # do something with var we haven't done before
    return var

myvar = func4(func3(func2(func1(myvar))))
# or
myvar = func3(func4(func2(func1(myvar))))
# or
myvar = func3(func2(func4(func1(myvar))))
# or
myvar = func3(func2(func1(func4(myvar))))
# or
myvar = func4(func2(func3(func1(myvar))))
# or
# ...etc...
# or (finally)
myvar = func1(func2(func3(func4(myvar))))

Answer 1

要获取所有函数排列，您可以使用

itertools.permutations

还可以将一系列函数应用于一个值，您可以使用

functools.reduce

import functools
import reduce

def applyfunc(val, func):
    return func(val)

def apply_sequence(sequence, val):
    return functools.reduce(applyfunc, sequence, val)

def apply_permutations(func_list, val):
    return map(apply_sequence,
               itertools.permutations(sequence))


# use it like this:

for v in apply_permutations([f1, f2, f3, f4], val):
    print v