5 Best Ways to Merge Strings into a List in Python

πŸ’‘ Problem Formulation: Python developers often need to combine multiple strings into a single list. This is a common task when handling textual data, where strings need to be aggregated for processing or output. For example, joining a series of user-input strings into a list structure to be used later. The desired outcome is, given several strings, to assemble them into one cohesive list object.

Method 1: Using the List Append Method

Appending strings to a list one by one is the most straightforward method. It’s highly readable and easy to understand. The append() method simply adds its argument as a single element to the end of a list. The length of the list increases by one.

Here’s an example:

strings = ["Hello", "world!"]
combined_list = []
for string in strings:
    combined_list.append(string)

Output:

['Hello', 'world!']

This snippet iteratively adds each string from the strings array to the combined_list using a for loop and the append() method, resulting in a list of strings.

Method 2: Using the List Extend Method

The extend() method is perfect when you need to merge an iterable of strings (like a list or tuple) with another list. As opposed to append(), extend() unpacks the iterable and adds each element to the list.

Here’s an example:

first_list = ["Hello"]
second_list = ["beautiful", "world!"]
first_list.extend(second_list)

Output:

['Hello', 'beautiful', 'world!']

The extend() method takes all items from second_list and adds them to the first_list, which makes it easy to concatenate multiple lists of strings.

Method 3: Using the Plus Operator

The plus operator (+) is a quick and elegant way to concatenate two lists in Python. It’s an intuitive and widely-used method to join lists, however, it creates a new list instead of modifying the original one.

Here’s an example:

list_one = ["The", "quick"]
list_two = ["brown", "fox"]
combined_list = list_one + list_two

Output:

['The', 'quick', 'brown', 'fox']

Simply by using the ‘+’ operator, list_one and list_two are combined into a new list combined_list with all the elements in the correct order.

Method 4: Using List Comprehension

List comprehension offers a concise way to create a new list by concatenating a group of strings, based on existing strings or a range of values. It is more compact and arguably faster, especially for large datasets.

Here’s an example:

names = ["Alice", "Bob", "Charlie"]
greetings = ["Hello " + name for name in names]

Output:

['Hello Alice', 'Hello Bob', 'Hello Charlie']

This list comprehension joins “Hello ” with every name in the names list, creating a new list greetings with personalized greetings.

Bonus One-Liner Method 5: Using the * Operator

The asterisk (*) operator is commonly used for repetitively adding elements to a list, but it can also be used for concatenation in a compact form known as starred expression.

Here’s an example:

phrase_parts = ["Code", "Review"]
full_phrase = [*phrase_parts, "Day"]

Output:

['Code', 'Review', 'Day']

The starred expression *phrase_parts unpacks the contents of the phrase_parts list into the new full_phrase list, which is then extended with an additional string “Day”.

Summary/Discussion

  • Method 1: List Append. Simple and clear. It’s great for iteratively building a list of strings. However, it can be less efficient than other methods if used in large scale due to creating a new list object each time.
  • Method 2: List Extend. Efficiently combines lists without creating unnecessary copies. Ideal for merging two or more lists, but not as handy for adding single strings to a list.
  • Method 3: Plus Operator. Intuitive for small lists or when the original lists are not needed afterward. However, since it creates a new list, it is not memory efficient for large lists.
  • Method 4: List Comprehension. Provides a slick and compact approach for merging strings. It performs well with large datasets and its one-liner appeal can be very pythonic.
  • Bonus Method 5: Starred Expression. A neat trick for quick and readable string concatenations in a list. It shines for its conciseness but may not be as familiar to newcomers.