使用装饰器更改已装饰 function 的参数

Question

Background

I want to perform different methods to the same data. Different methods are variants of an original method, only with different arguments for param:p3 .

# This is original method
def method(p1,p2,p3,data):
    return data + p1 + p2 + p3
method(p1=1, p2=2, p3=3, data=10)

16

# By changing param:p3, I can define 3 methods based on original method.
# but it seems stupid and very unclear...
def method1(*args, **kw):
    return method(*args, **kw, p3 = 1)
def method2(*args, **kw):
    return method(*args, **kw, p3 = 2)
def method3(*args, **kw):
    return method(*args, **kw, p3 = 3)
method1(p1=1,p2=2,data =10),\
method2(p1=1,p2=3, data =100)

(14,106)

Question

Is there any decorator to revise my original method to any variant, like method1 ?

# After decorated, method equals to method1
@decorator(p3 = 1)
def method(p1,p2,p3,data):
    return data + p1 + p2 + p3

# After decorated, method equals to method2
@decorator(p3 = 2)
def method(p1,p2,p3,data):
    return data + p1 + p2 + p3

Or, Shouldn't I use a decorator to satisfy my demand, maybe a class instead?

Answer 1

To flesh out rchome's comment, you can use functools.partial as follows:

>>> from functools import partial
>>> def method(p1,p2,p3,data):
...     return data + p1 + p2 + p3
>>> method1 = partial(method, p3=1)
>>> method2 = partial(method, p3=2)
>>> method3 = partial(method, p3=3)
>>> method1(p1=1,p2=2,data=10)
14
>>> method2(p1=1,p2=2,data=10)
15
>>> method3(p1=1,p2=2,data=10)
16

Answer 2

We can use decorator to do the same thing as follows:

# this is a decorator factory
def de_fac(**out_kw):
    def my_decorator(f):
        def wrapper(*args, **kw):
            print('inside function arguments:',{*args})
            print('inside function keywords:',{**kw})
            print("outside decorator factory\'s arguments:", {**out_kw})
            # override {**kw} with {**out_kw}
            return f(*args, **{**kw, **out_kw})
        return wrapper
    return my_decorator


@de_fac(p3=1)
def method_to_be_dec(p1,p2,p3,data):
    return data + p1 + p2 + p3

# it's same
method_to_be_dec(p1=1, p2=2, data=10), method1(p1=1, p2=2, data=10)

inside function arguments: set()
inside function keywords: {'p1': 1, 'p2': 2, 'data': 10}
outside decorator factory's arguments: {'p3': 1}
(14, 14)