将Lambda表达式转换为简单函数

Question

I'm curious if it is possible to avoid lambda expressions in the following case.

For example using lambda expression I can simple define a function that returns a lambda exp.

def square_fun(a,b,c):
   return lambda x: a*x**2 + b*x + c

After we can call it using:

f = square_fun(1,2,3)

f(1) # here x = 1

How can I get the same behaviour avoiding lambda expression?

for example, square_fun must return another function

def square_fun(a,b,c):
   return f...

Answer 1

In python you can define a function inside another function, so the following snippet should give you the same behavior:

def square_fun(a, b, c):
    def result(x):
        return a*x**2 + b*x + c
    return result

f = square_fun(1, 2, 3)
print(f(1))
# Should print 6

So, I'll try to explain what's going on here:

1. In the line f = square_fun(1, 2, 3) , f will actually be mapped to the internal function (aka. result )
2. Please note that return result does not have the () at the end, hence the function is not called yet
3. The function gets called in print(f(1)) and the variable x takes 1 as its value
4. Finally the result function returns the computed value using x , and a , b and c (from square_fun(1, 2, 3) )

You can find additional info here => https://www.learnpython.org/en/Closures

Answer 2

You can also use functools.partial :

from functools import partial


def square_fun(x, a, b, c):
    return a * x ** 2 + b * x + c


f = partial(square_fun, a=1, b=2, c=3)
print(f(1))
# should print 6