partial function of python

Abstract: The core design principle of python is simplicity - guided by this principle, lambda expressions and partial functions were born: both make function calls concise. This article mainly introduces you to the application of partial functions.

Why use partial functions

If we define a function, say add(one,two,three,four) to add four numbers, there are many functions in the upper layer that need to call this function. In these calls, 80% of the passed parameters are one=1, two=20. If we enter the same parameters every time, it is tedious and wasteful. Of course, we can solve this problem by default parameters; but if In addition, we also need the parameters to be one=2, two=10? Therefore, we need a function that can convert a function of any number of parameters into a function object with the remaining parameters.

Through the above, we roughly understand what a partial function is: simply put, a partial function is the realization of a function with fixed parameters, so we need:

1) Name the partial function

2) Passing fixed parameters

from functools import partial
def add(a,b):
    return a+b

p1 = partial(add, 100)

p2 = partial(add, 90)

print('p1=', p1(99))

print('p2=', p2(30))

'''
result:
p1=199
p2=120    
'''

Use partial functions

Combine getattr reflection

            import functools
            class RequestContext(object):
                def __init__(self):
                    self.request = "xxxxx"
                    self.session = "iusdkfjlskdf"

            obj = RequestContext()
            # obj.request
            # obj.session



            def get_data(name):
                return getattr(obj,name)

            request_proxy = functools.partial(get_data,'request')
            session_proxy = functools.partial(get_data,'session')

            request = request_proxy()
            print(request)

            session = session_proxy()
            print(session)

Result: 
"xxxxx"

"iusdkfjlskdf"