How To Apply A Function To Each Element Of A Tuple?

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This article shows you how to apply a given function to each element of a tuple.

The best way to apply a function to each element of a tuple is the Python built-in map(function, iterable) function that takes a function and an iterable as arguments and applies the function to each iterable element. An alternate way is to use list comprehension

Note: All the solutions provided below have been verified in Python 3.9.5.

Problem Formulation

Imagine the following tuple of strings in Python.

my_tuple = ('you',  'cannot',  'exercise',  
            'away',  'a',  'bad',  'diet')

How does one apply a function string.upper() to uppercase each string in the tuple?


I’ll start with the “naive approach” first and show you the more Pythonic solutions afterward. So, let’s get started!

Method 1: Simple For Loop

The above problem, like many others, has quite a simple solution in Python.

A simple solution uses a vanilla Python loop to iterate over each element of the original tuple. Apply the function to each element in the loop body and store the elements in a mutable container type such as a list. Finally, create a new tuple using the tuple() constructor and pass the new elements as arguments.

The result is a tuple of new elements — here stored in the variable new_tuple after applying the function string.upper() to each element of a Python tuple:

my_tuple = ('you',  'cannot',  'exercise',  
            'away',  'a',  'bad',  'diet')

tmp = []
for element in my_tuple:
    # Apply function to each element here:

# Create a new tuple here:
new_tuple = tuple(tmp)

# ('YOU', 'CANNOT', 'EXERCISE', 'AWAY', 'A', 'BAD', 'DIET')

However, this is not the most Pythonic way to approach this problem.

Method 2: map()

Using the Python built-in map() function is the most efficient and elegant way to solve the problem. The map(function, iterable) function takes a function and an iterable as arguments and applies the given function to each element of the iterable.

For example, to apply the string.upper() function to each element of a Python tuple, use the map(str.upper, my_tuple) function to obtain a generator object. Now, convert the result to a tuple using the tuple() constructor and you’ve solved the problem!

This method is shown in the following code snippet:

# 'my_tuple' is the original tuple whose string elements need to be
# fully uppercased. Note that 'my_tuple' is an object of the Python
# built-in Tuple class. Lists, Sets, Dicts and Tuples are considered
# iterables.
my_tuple = ('you',  'cannot',  'exercise',  'away',  'a',  'bad',  'diet')

# Use the upper() function of Python's built-in str class, to modify
# each element of the my_tuple iterable.
my_generic_iterable = map(str.upper, my_tuple)
# map() returns an iterable (or generator) object.
# It contains all the modified elements. Generators are temporary container
# objects. They can be iterated upon only once, to extract the elements
# within them. For example, use the 'tuple()' constructor to go thru each
# element of the 'my_generic_iterable' generator and generate a tuple.
new_tuple = tuple(my_generic_iterable)

# Output:
# ['YOU', 'CANNOT', 'EXERCISE', 'AWAY', 'A', 'BAD', 'DIET']

If you need a quick explanation of the map() function, feel free to watch my training video here:

Mastering the Python Map Function [+Video]

Personally, I’d use the following method—but this is only a matter of personal style.

Method 3: Generator Expression

You can use generator expressions to apply a function to each element of a tuple.

Here’s how to accomplish that:

my_tuple = ('you',  'cannot',  'exercise',  
            'away',  'a',  'bad',  'diet')
new_tuple = tuple(str.upper(x) for x in my_tuple)

# Output:
# ['YOU', 'CANNOT', 'EXERCISE', 'AWAY', 'A', 'BAD', 'DIET']

Generator expressions are similar to list comprehensions. You can learn more about list comprehensions in the following video—generator expressions work analogously but are more generally applicable:

A Simple Introduction to List Comprehension in Python

Related Video

The following video shows how to apply a function to each element of a Python list. This is very similar to our problem, so it applies analogously to the solutions presented here:

How To Apply A Function To Each Element Of A Python List?

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