What is the itertools.starmap() method in Python?

Overview

The itertools module provides functions help in iterating through iterables. The starmap() method of the itertools module returns an iterator that applies to the given function by passing the elements of the specified iterable as arguments to the function. starmap() works similar to map() with the only difference in the way the arguments are passed to the function, meaning map() expects function(x,y) while starmap() expects function(*x).

The output of the method can be accessed in the following ways:

• Converting it to a list using list() constructor.
• Converting it to a tuple using tuple() constructor.
• Using a for loop.
• Using the next() method on the output map object.

Note: starmap() expects every element of the iterable to be iterable. If not TypeError is thrown.

Syntax

itertools.starmap(function, iterable)

Parameters

• function: The function to be applied.
• iterable: The iterable of iterables.

Applying a user-defined function

Explanation

• Line 1: We import the itertools module.
• Line 3: We call an iterable of iterables called lst.
• Lines 5–6: We define a function called func that takes two arguments and returns the product of the two arguments.
• Line 8: We apply func to lst using the starmap() method. The result is stored in ret_val.
• Line 10: We print ret_val and lst.

Applying an in-built function

Explanation

• Line 1: We import the itertools module.
• Line 3: We define an iterable of iterables called lst.
• Line 5: We apply the built-in pow function to lst using the starmap() method. We store the results in ret_val.
• Line 10: We print ret_val and lst.

Applying a lambda function

Explanation

• Line 1: We import the itertools module.
• Line 3: We define an iterable of iterables called lst.
• Line 5: We define a lambda function called lambda_div that takes two arguments, that is (x, y) and returns the result of x / y.
• Line 8: We apply lambda_div to lst using the starmap() method. We store the results in ret_val.
• Line 10: We print ret_val and lst.

The TypeError use case

In the example above, as lst is not an iterable of iterables, the method throws a TypeError indicating that int object in lst is not an iterable.