Python Filter List of Strings endswith() : Chris

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February 05, 2024
Python Filter List of Strings endswith()
by: Chris
blow post content copied from  Be on the Right Side of Change
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Problem Formulation

Imagine a scenario where you have a list of strings and your goal is to filter out only those strings that end with a specific suffix. Here’s a minimal example with the desired input and output:

Input:

my_strings = ['hello.py', 'readme.md', 'test.py', 'documentation.txt']
suffix = '.py'

Output:

filtered_strings = ['hello.py', 'test.py']

Method 1: Using a Loop with endswith()

Python’s endswith() string method can be used within a for-loop to test if each element in the list ends with the provided suffix. If the condition is met, the element can be added to a new list.

Here’s an example:

my_strings = ['hello.py', 'readme.md', 'test.py', 'documentation.txt']
suffix = '.py'
filtered_strings = []

for string in my_strings:
    if string.endswith(suffix):
        filtered_strings.append(string)

print(filtered_strings)

In this example, filtered_strings will only contain the elements from my_strings that have the .py suffix.

Method 2: Using filter() with a Lambda Function

The filter() function in conjunction with a lambda function can provide a more concise way to accomplish the filtering. The filter() function applies a function to every item of the iterable (list) and returns an iterator that gets the items for which the function returns True.

Here’s an example:

my_strings = ['hello.py', 'readme.md', 'test.py', 'documentation.txt']
suffix = '.py'
filtered_strings = list(filter(lambda x: x.endswith(suffix), my_strings))

print(filtered_strings)

Here, filter() is used with a lambda function that returns True for items ending with .py. The result is then cast back to a list.

Method 3: List Comprehension

List comprehensions provide a more Pythonic and readable approach to creating lists based on existing lists. It’s a concise way to apply an if condition to filter items.

Here’s an example:

my_strings = ['hello.py', 'readme.md', 'test.py', 'documentation.txt']
suffix = '.py'
filtered_strings = [s for s in my_strings if s.endswith(suffix)]

print(filtered_strings)

The list comprehension checks each string’s suffix and includes it in the new list if the check passes.

Method 4: Using filter() with the str.endswith() Method Directly

Instead of a lambda function, you can use the endswith() method directly in the filter() function to achieve the same result.

Here’s an example:

my_strings = ['hello.py', 'readme.md', 'test.py', 'documentation.txt']
suffix = '.py'
filtered_strings = list(filter(str.endswith(suffix), my_strings))

print(filtered_strings)

Here, str.endswith(suffix) is treated as a function that filter() can apply to each item in the list my_strings.

Method 5: Using Regular Expressions with re

For more complex string ending patterns, regular expressions can be used. The re module provides a powerful way to filter strings based on patterns.

Here’s an example:

import re

my_strings = ['hello.py', 'readme.md', 'test.py', 'documentation.txt']
suffix = '\.py$'  # $ denotes the end of the string
filtered_strings = [s for s in my_strings if re.search(suffix, s)]

print(filtered_strings)

This method compiles a regular expression pattern and checks if any strings in the list match that pattern, specifically looking for strings that end with .py.

Bonus One-Liner Method 6: Using fnmatch.filter()

When working with files and patterns, you can use the fnmatch module. Its filter() function matches strings using Unix shell-style wildcards.

Here’s an example:

import fnmatch

my_strings = ['hello.py', 'readme.md', 'test.py', 'documentation.txt']
suffix_pattern = '*.py'  # Unix shell-style wildcard
filtered_strings = fnmatch.filter(my_strings, suffix_pattern)

print(filtered_strings)

The fnmatch library filters the list based on the pattern *.py, returning only strings that end with .py.

Summary/Discussion

To sum up, we’ve explored six different methods to filter a list of strings in Python that end with a specific suffix:

  1. Using a loop with endswith()
  2. Using filter() with a lambda function
  3. Using list comprehension
  4. Using filter() with str.endswith() directly
  5. Using regular expressions with re
  6. Using fnmatch.filter()

For everyday use, list comprehensions and filter() are often the most straightforward. However, regular expressions are useful for more complex patterns, and fnmatch is handy when working with filename patterns.


February 05, 2024 at 05:28PM
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