如何使用装饰器向python中的函数发送参数

Question

I have a set of functions in python that gets the same 2 parameters + other parameters.

def myMethodA (param1, param2, specificParm)
    do code

 def myMethodB (param1, param2, specificParm1 specificParam2)
    do code

I waned to create a decorator that replace the need to call with the first 2 parameters by pushing the parameters before calling the function:

@withParams()
def myMethodA (specificParam)
        do code

But if I omit the parameters then the decorator can't call it either and if I leave them then the caller need to specify them as well.

anyway to solve this? Can I do something with args* but still have named parameters for specificParam? Also, How can I reference param1 and param2 inside myMethodA

Answer 1

It sounds like you may want functools.partial . It returns a new function with some parameters already specified:

import functools

def withParams(func):
    return functools.partial(func,1,2)

@withParams
def myMethodA (param1, param2, specificParam):
    print(param1,param2,specificParam)

@withParams
def myMethodB (param1, param2, specificParam1, specificParam2):
    print(param1,param2,specificParam1, specificParam2)

myMethodA(10)
myMethodB(12,13)

 1 2 10 1 2 12 13 

Answer 2

You can add those two parameters when you call the function in the decorator's wrapper function as part of the kwargs . All decorated functions will automatically have those two parameters passed as keyword arguments before making the call:

def withParams(func):
    def wrapper(*args, **kwargs):
        kwargs['param1'] = 1
        kwargs['param2'] = 2
        return func(*args, **kwargs)
    return wrapper

@withParams
def add(specificparam, *args, **kwargs):
      print(specificparam)  # 3
      print(args)           # (4,)
      print(kwargs)         # {'param2': 2, 'param1': 1}
      return specificparam + sum(args) + sum(kwargs.values())

print(add(3,4)) # 10

You can drop the args part if all you'll be passing from the main function call are the specific parameters for each function.

Answer 3

I'd recommend you go old school, and just reassign the names using functools.partial :

# module foo

def func1(common_1, common_2, specific_1):
    pass

def func2(common_1, common_2, specific_2, specific_3):
    pass

Then elsewhere (or lower in the file, if you like) you can do this:

import functools

import foo

common_args = (1, 'fred')
foo.func1 = functools.partial(foo.func1, *common_args)
foo.func2 = functools.partial(foo.func2, *common_args)

# ...

foo.func1('special')

foo.func2('equally special', 'but different')

Answer 4

Sounds like you need functools.partial , to pre-populate the "constant" parameters:

>>> from functools import partial

>>> def myMethodA(param1, param2, specificParm):
        print("myMethodA(", param1, param2, specificParm, ")")

>>>> def myMethodB (param1, param2, specificParm1, specificParam2):
        print("myMethodB(", param1, param2, specificParm1, specificParam2, ")")

>>> preMethodA = partial(myMethodA, "p1", "p2")
>>> preMethodB = partial(myMethodB, "p1", "p2")
>>> preMethodA(34)
myMethodA( p1 p2 34 )
>>> preMethodB(8, 9)
myMethodB( p1 p2 8 9 )