How do I return a function from within a Python function?

Python supports first-class functions. In fact, all functions in Python are first-class functions. Python can return functions from functions, store functions in collections (such as lists), and generally treat functions like any variable or object. In Python, functions can return functions because they are treated as first-class objects. This means you can assign a function to a variable, pass it as an argument to another function, or use it in a function’s return value. It’s also possible to define functions within other functions and return them.

In this code, the outer function defines and returns the inner function. You can then call the outer function and assign its return value to a variable:

Now, f is a reference to the inner function. You can call it like any other function:

Example

def outer():
def inner():
print("Hello from inner!")
return inner
f = outer()
f()

Output

Hello from inner!

Returning a Function with Parameters

You can use parameters in the returned function in different ways. One way is to pass them to the outer function and use them in the inner function.

In this code, the outer function takes one parameter, x, and returns a function that prints its value. You can call it like this:

Example

def outer(x):
def inner():
print("x is", x)
return inner
f = outer(10)
f()

Output

x is 10

Another way is to pass arguments to the inner function when calling it.

In this code, the outer function returns a function that takes the argument y and prints its value. You can call it like this:

Example

def outer():
def inner(y):
print("y is", y)
return inner
f = outer()
f(20)

Output

y is 20

Higher-Order Functions

In Python, a function can return another function as its result. This is called a “higher-order function.”

Example

def adder(x):
def inner(y):
return x + y
return inner

In this example, we define a function called adder that takes a single argument, x. Inside adder, we define another function called inner that takes a single argument, y, and returns the sum of x and y.

Instead of returning the sum directly, adder returns the inner function itself. This means that when we call adder(1), for example, we get a new function that adds 1 to its argument.

Returning Functions from Functions in Python

To return a function from a function in Python, you can define a new function within the first function and then return it. This technique is called nested functions or closures. You can then assign the returned function to a variable and call it later.

Example

def adder(x):
def inner(y):
return x + y
return inner

add_one = adder(1)
print(add_one(5)) # prints 6

Output

6

In this example, adder is a function that takes one argument, x, and returns a new function, inner. The function inner takes one argument, y, and returns the sum of x and y. When we call adder(1), it returns a new function object inner with x set to 1. We can then assign this new function object to the variable add_one and call it with the argument 5, which will result in the output being 6.

Overall, this pattern can be used to write more flexible and reusable code, especially when combined with other higher-level programming concepts like closures and currying.

Example

def create_multiplier(factor):
def multiplier(number):
return number * factor
return multiplier

double = create_multiplier(2)
triple = create_multiplier(3)

print(double(5)) # Output: 10
print(triple(5)) # Output: 15

Output

10
15

In this example, create_multiplier is a function that takes a factor argument and returns a new function, multiplier. The function multiplier takes a number argument and returns the product of number and factor. We create two new functions, double and triple, by calling create_multiplier with different factors. We can then call these functions with different numbers to get the desired output.

It’s important to note that each time we call create_multiplier, it returns a new function object. This means that even though they were created using the same create_multiplier function, double and triple are different functions.

Returning Functions from Functions in Python
Returning functions from functions in Python can be a powerful tool for creating flexible and reusable code. By returning a function, we can abstract away the details of how a function works and provide a higher-level interface to the user. In this article, we’ll explore how to return functions in Python using nested functions or lambda functions.

Example: Nested Functions

def adder(x):
def inner(y):
return x + y
return inner

add_one = adder(1)
print(add_one(5)) # Output 6

Output

6

In this example, adder is a function that takes one argument, x, and returns a new function, inner. The function inner takes one argument, y, and returns the sum of x and y. When we call adder(1), it returns a new function object, inner, with x set to 1. We then assign this new function to the variable add_one. When we call add_one(5), it is equivalent to calling inner(5) with x set to 1.

Overall, this pattern can be used to write more flexible and reusable code, especially when combined with other higher-level programming concepts like closures and currying.

Here is another example of a function returning a function in Python, but this time using a lambda function:

Example: Lambda Function

def make_incrementor(n):
return lambda x: x + n

increment_by_five = make_incrementor(5)
increment_by_ten = make_incrementor(10)

print(increment_by_five(3)) # Output: 8
print(increment_by_ten(3)) # Output: 13

Output

8
13

In this example, make_incrementor is a function that takes one argument, n, and returns a lambda function that takes one argument, x, and returns the sum of x and n. When we call make_incrementor(5), it returns a new lambda function object that adds 5 to its argument. We then assign this new function to the variable increment_by_five. When we call increment_by_five(3), it is equivalent to calling (lambda x: x + 5)(3).

By returning a function from a function, we can create more flexible and reusable code in Python. Whether you use nested functions or lambda functions, the ability to return functions as values is a powerful feature in your programming toolset.

In summary, returning functions from functions in Python can use either nested functions or lambda functions, and it allows us to create more flexible and reusable code. By returning a function, we can abstract the details of how the function works and provide a higher-level interface to the user.