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Currying function with example in Python

Python currying function: Here, we are going to learn about the currying function with example in Python.
Submitted by Yash Khandelwal, on March 31, 2019

In terms of Mathematics and Computer science, currying is the approach/technique by which we can break multiple-argument function to single argument function.

Mathematical illustration: h(x)=g(f(x))

The composition of two functions is a chaining process in which the output becomes the input for the outer function.

    def currying( g , f ):
        def h(x):
            return g(f(x))
        return h

In the technical term "Currying is the process of transforming a function that takes 'n' arguments into a series of 'n' function that only takes the one argument each."

In problem-solving approach, currying is to be done to simplify the programming i.e. execution of the function which takes multiple arguments into the single - single argument functions.

Example code 1:

def f(a):
    def g(b, c, d, e):
        print(a, b, c, d, e)
    return g #as in f it return g this is currying
 
f1 = f(1)

f1(2,3,4,5)

Output

1 2 3 4 5

Explanation of the above code:

Now, f(1) returns the function g(b, c, d, e) which, for all b, c, d, and e, behaves exactly like f(1, b, c, d, e). Since g is a function, it should support currying as well.

Example code 2:

def f(a):
    def g(b):
        def h(c):
            def i(d):
                def j(e):
                    print(a, b, c, d, e)
                return j  #return to function i
            return i      #return to function h
        return h          #return to function g
    return g              #return to function f
 
f(1)(2)(3)(4)(5)

Output

1 2 3 4 5

Explanation of the above code:

In the code we have, X(a,b,c,d,e) = f(g(h(i(j(a,b,c,d,e))))

Here, the concept is of nesting of one function to another and hence the result of one function get stored or recorded in another function as a chain of functions.

Note: Now f(a,b,c,d,e) is no more i.e. now f no more take 5 arguments.

Python example of currying function to convert INR to pounds

# program to covert the Indian Rupee to Pound
# Demonstrating  Currying of composition of function
def change(b, c): 
    def a(x): #by currying function
        return b(c(x)) 
    return a 
      
def IR2USD(ammount):  
    return ammount*0.014  # as 1IR=0.014USD
      
def USD2Pound(ammount):  # Function converting USD to Pounds 
    return ammount * 0.77 
      
if __name__ == '__main__': 
    Convert = change(IR2USD,USD2Pound )
    
    e = Convert(565)
    print("Conveted Indian Rupee to Pound:")
    print('565 INDIAN RUPEES =',e,'PoundSterling')      

Output

Conveted Indian Rupee to Pound:
565 INDIAN RUPEES = 6.0907 PoundSterling