Checking Prefixes and Suffixes (startswith, endswith)

When working with text data, you often need to check whether a string begins or ends with a specific sequence of characters. Python provides two simple methods for this: startswith() and endswith(). These are incredibly useful when validating file extensions, checking URL protocols, or parsing log entries.

⚙️ What Are Prefix and Suffix Checks?

• A prefix is the beginning portion of a string. For example, in the string "hello_world.txt", the prefix "hello" appears at the start.
• A suffix is the ending portion of a string. In the same example, the suffix ".txt" appears at the end.
• The startswith() method checks if a string starts with a given prefix.
• The endswith() method checks if a string ends with a given suffix.
• Both methods return a boolean value: True if the condition is met, False otherwise.

🛠️ Using startswith()

• The basic syntax is: string.startswith(prefix)
• It returns True if the string begins with the specified prefix.
• Example: "report_final.pdf".startswith("report") returns True
• Example: "data_2024.csv".startswith("log") returns False
• You can also specify a starting position: string.startswith(prefix, start)
• Example: "error_log.txt".startswith("log", 6) returns True (starts checking from index 6)

🛠️ Using endswith()

• The basic syntax is: string.endswith(suffix)
• It returns True if the string ends with the specified suffix.
• Example: "image.png".endswith(".png") returns True
• Example: "document.pdf".endswith(".docx") returns False
• You can also check within a range: string.endswith(suffix, start, end)
• Example: "backup_2024_old.zip".endswith("old", 0, 14) returns True (only checks characters from index 0 to 13)

📊 Checking Multiple Options

Both methods accept a tuple of prefixes or suffixes to check against:

• startswith() with a tuple: string.startswith(("http", "https", "ftp")) returns True if the string starts with any of those protocols
• endswith() with a tuple: filename.endswith((".jpg", ".png", ".gif")) returns True if the file has any of those image extensions
• This is much cleaner than writing multiple or conditions

🕵️ Practical Examples

⚡ Common Use Cases

• File processing: Check file extensions before reading or writing files
• URL validation: Verify that a URL uses the expected protocol
• Log parsing: Identify log entries by their starting keywords (INFO, WARNING, ERROR)
• Data cleaning: Remove or process strings that begin or end with specific characters
• Configuration checks: Validate that configuration keys follow naming conventions

🧠 Key Takeaways

• startswith() and endswith() are case-sensitive by default
• Both methods accept a tuple for checking multiple prefixes or suffixes at once
• You can specify start and end indices to limit the search range
• These methods return True or False, making them perfect for conditional statements
• They are efficient and readable alternatives to using slicing or regular expressions for simple prefix/suffix checks

The startswith() and endswith() methods check whether a string begins or ends with a specified substring, returning True or False.

🔧 Example 1: Basic prefix check with startswith()

Check if a simple word starts with a given letter.

text = "engineer"
result = text.startswith("eng")
print(result)

📤 Output: True

🔧 Example 2: Basic suffix check with endswith()

Check if a filename ends with a specific file extension.

filename = "report.pdf"
result = filename.endswith(".pdf")
print(result)

📤 Output: True

🔧 Example 3: Case sensitivity matters

Both methods are case-sensitive — uppercase and lowercase are treated as different.

text = "Python"
result_start = text.startswith("python")
result_end = text.endswith("ON")
print(result_start)
print(result_end)

📤 Output: False
📤 Output: False

🔧 Example 4: Checking multiple possible prefixes at once

Pass a tuple of strings to check if the string starts with any of them.

url = "https://docs.python.org"
result = url.startswith(("http://", "https://"))
print(result)

📤 Output: True

🔧 Example 5: Practical use — validating log file names

Engineers often need to verify file naming conventions before processing.

log_file = "error_2024_01_15.log"
starts_correctly = log_file.startswith("error_")
ends_correctly = log_file.endswith(".log")
print(starts_correctly)
print(ends_correctly)

📤 Output: True
📤 Output: True

📊 Comparison Table: startswith() vs endswith()

When working with text data, you often need to check whether a string begins or ends with a specific sequence of characters. Python provides two simple methods for this: startswith() and endswith(). These are incredibly useful when validating file extensions, checking URL protocols, or parsing log entries.

⚙️ What Are Prefix and Suffix Checks?

• A prefix is the beginning portion of a string. For example, in the string "hello_world.txt", the prefix "hello" appears at the start.
• A suffix is the ending portion of a string. In the same example, the suffix ".txt" appears at the end.
• The startswith() method checks if a string starts with a given prefix.
• The endswith() method checks if a string ends with a given suffix.
• Both methods return a boolean value: True if the condition is met, False otherwise.

🛠️ Using startswith()

• The basic syntax is: string.startswith(prefix)
• It returns True if the string begins with the specified prefix.
• Example: "report_final.pdf".startswith("report") returns True
• Example: "data_2024.csv".startswith("log") returns False
• You can also specify a starting position: string.startswith(prefix, start)
• Example: "error_log.txt".startswith("log", 6) returns True (starts checking from index 6)

🛠️ Using endswith()

• The basic syntax is: string.endswith(suffix)
• It returns True if the string ends with the specified suffix.
• Example: "image.png".endswith(".png") returns True
• Example: "document.pdf".endswith(".docx") returns False
• You can also check within a range: string.endswith(suffix, start, end)
• Example: "backup_2024_old.zip".endswith("old", 0, 14) returns True (only checks characters from index 0 to 13)

📊 Checking Multiple Options

Both methods accept a tuple of prefixes or suffixes to check against:

• startswith() with a tuple: string.startswith(("http", "https", "ftp")) returns True if the string starts with any of those protocols
• endswith() with a tuple: filename.endswith((".jpg", ".png", ".gif")) returns True if the file has any of those image extensions
• This is much cleaner than writing multiple or conditions

🕵️ Practical Examples

⚡ Common Use Cases

• File processing: Check file extensions before reading or writing files
• URL validation: Verify that a URL uses the expected protocol
• Log parsing: Identify log entries by their starting keywords (INFO, WARNING, ERROR)
• Data cleaning: Remove or process strings that begin or end with specific characters
• Configuration checks: Validate that configuration keys follow naming conventions

🧠 Key Takeaways

• startswith() and endswith() are case-sensitive by default
• Both methods accept a tuple for checking multiple prefixes or suffixes at once
• You can specify start and end indices to limit the search range
• These methods return True or False, making them perfect for conditional statements
• They are efficient and readable alternatives to using slicing or regular expressions for simple prefix/suffix checks

The startswith() and endswith() methods check whether a string begins or ends with a specified substring, returning True or False.

🔧 Example 1: Basic prefix check with startswith()

Check if a simple word starts with a given letter.

text = "engineer"
result = text.startswith("eng")
print(result)

📤 Output: True

🔧 Example 2: Basic suffix check with endswith()

Check if a filename ends with a specific file extension.

filename = "report.pdf"
result = filename.endswith(".pdf")
print(result)

📤 Output: True

🔧 Example 3: Case sensitivity matters

Both methods are case-sensitive — uppercase and lowercase are treated as different.

text = "Python"
result_start = text.startswith("python")
result_end = text.endswith("ON")
print(result_start)
print(result_end)

📤 Output: False
📤 Output: False

🔧 Example 4: Checking multiple possible prefixes at once

Pass a tuple of strings to check if the string starts with any of them.

url = "https://docs.python.org"
result = url.startswith(("http://", "https://"))
print(result)

📤 Output: True

🔧 Example 5: Practical use — validating log file names

Engineers often need to verify file naming conventions before processing.

log_file = "error_2024_01_15.log"
starts_correctly = log_file.startswith("error_")
ends_correctly = log_file.endswith(".log")
print(starts_correctly)
print(ends_correctly)

📤 Output: True
📤 Output: True

📊 Comparison Table: startswith() vs endswith()