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How to convert a Map object to a List in Python

The map() function in Python returns a map object (an iterator) that applies a function to every item in an iterable.

This guide explores various methods for converting map objects to lists, allowing you to work with the results in a standard list format. We will cover using the list() constructor, iterable unpacking, list comprehensions, and loops.

Converting Map Objects with the list() Constructor​

The simplest way to convert a map object to a list is by using the list() constructor. The list() constructor takes an iterable (like a map object) and returns a new list object containing all the items from the iterable.

my_list = ['1.1', '2.2', '3.3']
new_list = list(map(float, my_list))
print(new_list)         # Output: [1.1, 2.2, 3.3]
print(type(new_list))   # Output: <class 'list'>
  • The map(float, my_list) creates a map object which applies the function float() to each item in the my_list.
  • The list() constructor then converts this map object into a new list.

Iterating over Map Objects​

If you only need to access the elements from the map object, you can iterate directly using a for loop:

my_list = ['1.1', '2.2', '3.3']
map_obj = map(float, my_list)

for item in map_obj:
    print(item)

output

1.1
2.2
3.3

Converting Map Objects with Iterable Unpacking​

Another way to convert a map object to a list is by using the iterable unpacking operator (*). This operator unpacks the map object's elements, allowing them to be collected into a list:

my_list = ['1.1', '2.2', '3.3']
new_list = [*map(float, my_list)]
print(new_list)         # Output: [1.1, 2.2, 3.3]
print(type(new_list))   # Output: <class 'list'>
  • The * operator unpacks the elements from the map object which causes the list to be created.

Using List Comprehensions Instead of map()​

List comprehensions offer a concise way to achieve the same result as using map(), allowing you to apply an operation and collect the result into a list:

my_list = ['1.1', '2.2', '3.3']
new_list = [float(item) for item in my_list]
print(new_list)  # Output: [1.1, 2.2, 3.3]
  • The list comprehension [float(item) for item in my_list] iterates over each item in the my_list, converts it to a float and stores it in the new list.

Converting Map Objects with a for Loop​

You can also convert a map object to a list by iterating over the map object using a for loop and appending each value to the new list:

my_list = ['1.1', '2.2', '3.3']
map_obj = map(float, my_list)
new_list = []
for item in map_obj:
    new_list.append(item)
print(new_list) # Output: [1.1, 2.2, 3.3]
note

This approach allows more flexibility within the for loop, and performs the exact same function as the list() constructor approach.

Using a for Loop Instead of map()​

You can achieve the same result using a for loop directly on the original list:

my_list = ['1.1', '2.2', '3.3']
new_list = []
for item in my_list:
    new_list.append(float(item))

print(new_list) # Output: [1.1, 2.2, 3.3]

This creates an empty list new_list, then iterates over the original list and converts each item to float and appends the result to new_list.

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