In this tutorial, I will explain how to check if a string ends with a pattern in Python. As a Python developer working on a project for one of my New York clients, I came across a scenario where I needed to check if a string started with a specific pattern, I explored various Python’s built-in methods to perform this check efficiently. Let us learn more about this topic.
Check if a String Ends with a Pattern in Python
Python provides various methods to achieve this task. Let us see some important techniques.
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1. Use the endswith() Method
Python provides an easy method endswith() to check if a string ends with a specified suffix. This method is part of the string class and is very easy to use.
Syntax
str.endswith(suffix[, start[, end]])suffix: This can be a string or a tuple of strings to check for.start(optional): The position in the string where the check should start.end(optional): The position in the string where the check should end.
Example 1: Check File Extensions
Let’s say you are working with a list of filenames and you want to filter out only those that are CSV files.
filenames = ["data.csv", "report.pdf", "summary.csv", "notes.txt"]
csv_files = [file for file in filenames if file.endswith(".csv")]
print(csv_files)Output:
['data.csv', 'summary.csv']I have executed the above example code and added the screenshot below.
In this example, we use the endswith() method to check if each filename ends with .csv. The list comprehension filters out the filenames that do not match the pattern.
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Example 2: Validate URLs
Suppose you are working on a web application and you need to ensure that certain URLs end with /home.
urls = [
"https://example.com/home",
"https://example.com/about",
"https://example.com/home?user=123",
"https://example.com/contact"
]
home_urls = [url for url in urls if url.endswith("/home")]
print(home_urls)Output:
['https://example.com/home']I have executed the above example code and added the screenshot below.
Here, we use the endswith() method to check if each URL ends with /home. The list comprehension helps filter out URLs that do not match the pattern.
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2. Use Regular Expressions
While the endswith() method is simple and effective, but there are cases where you might need more flexibility. This is where regular expressions (regex) come into play. Python’s re module provides powerful tools for working with regex.
Example: Use Regex for More Complex Patterns
Let’s consider a scenario where you want to check if a string ends with either .com or .org.
import re
websites = ["https://example.com", "https://nonprofit.org", "https://example.net"]
pattern = re.compile(r"\.(com|org)$")
matching_websites = [site for site in websites if pattern.search(site)]
print(matching_websites)Output:
['https://example.com', 'https://nonprofit.org']I have executed the above example code and added the screenshot below.
In this example, we use a regex pattern to check if the string ends with .com or .org. The re.compile() function compiles the regex pattern, and the search() method checks if the pattern is found in the string.
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Performance Considerations
When working with large datasets or performance-critical applications, it’s important to consider the efficiency of your string operations. The endswith() method is highly optimized and performs well for most use cases. However, if you need to perform complex pattern matching, regular expressions might be more suitable despite their potential performance overhead.
Example: Performance Comparison
Let’s compare the performance of endswith() and regex for a simple pattern check.
import time
# Large list of strings
large_list = ["file{}.txt".format(i) for i in range(1000000)]
# Using endswith()
start_time = time.time()
txt_files = [file for file in large_list if file.endswith(".txt")]
end_time = time.time()
print("endswith() took:", end_time - start_time, "seconds")
# Using regex
pattern = re.compile(r"\.txt$")
start_time = time.time()
txt_files_regex = [file for file in large_list if pattern.search(file)]
end_time = time.time()
print("Regex took:", end_time - start_time, "seconds")Output:
endswith() took: 0.19353866577148438 seconds
Regex took: 0.46854496002197266 secondsI have executed the above example code and added the screenshot below.
In this example, the endswith() method is faster than the regex approach. Therefore, for simple suffix checks, endswith() is generally the better choice.
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Handle Case Sensitivity
By default, the endswith() method is case-sensitive. If you need to perform a case-insensitive check, you can convert the string to lowercase (or uppercase) before using endswith().
Example: Case-Insensitive Check
filenames = ["DATA.CSV", "report.PDF", "summary.csv", "NOTES.TXT"]
csv_files = [file for file in filenames if file.lower().endswith(".csv")]
print(csv_files)Output:
['DATA.CSV', 'summary.csv']In this example, we convert each filename to lowercase using the lower() method before checking if it ends with .csv.
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Check Multiple Suffixes
The endswith() method can also accept a tuple of suffixes, allowing you to check for multiple patterns at once.
Example: Multiple Suffixes
filenames = ["data.csv", "report.pdf", "summary.csv", "notes.txt"]
valid_files = [file for file in filenames if file.endswith((".csv", ".txt"))]
print(valid_files)Output:
['data.csv', 'summary.csv', 'notes.txt']In this example, we check if each filename ends with either .csv or .txt by passing a tuple of suffixes to the endswith() method.
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Conclusion
In this tutorial, I explained how to check if a string ends with a pattern in Python. I covered various methods, like the use of endswith() method for simple checks, regular expressions for more complex patterns, and performance considerations. I also discussed handling case sensitivity and checking multiple suffixes.
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I am Bijay Kumar, a Microsoft MVP in SharePoint. Apart from SharePoint, I started working on Python, Machine learning, and artificial intelligence for the last 5 years. During this time I got expertise in various Python libraries also like Tkinter, Pandas, NumPy, Turtle, Django, Matplotlib, Tensorflow, Scipy, Scikit-Learn, etc… for various clients in the United States, Canada, the United Kingdom, Australia, New Zealand, etc. Check out my profile.
