Python String startswith() Method

The startswith() method in Python is used to check if a string starts with a specific substring (prefix). It returns True if the string starts with the given value, and False otherwise.

Syntax

string.startswith(prefix[, start[, end]])

Parameters:

• prefix: The substring you want to check at the beginning.
• start (optional): The position to start checking from.
• end (optional): The position to stop checking (not included).

Returns:

• True if the string starts with the specified prefix; otherwise, False.

Example 1: Basic Usage

text = "hello world"
print(text.startswith("hello"))

True

Example 2: Case Sensitivity

print("Python".startswith("py"))

False

The method is case-sensitive.

Example 3: Using Start and End Parameters

msg = "Learn Python Programming"
print(msg.startswith("Python", 6))

True

It starts checking from index 6.

Example 4: Tuple of Prefixes

website = "https://example.com"
print(website.startswith(("http://", "https://")))

True

You can pass a tuple of prefixes to check against multiple options.

Common Use Cases

• Checking if a URL starts with "https://"
• Filtering strings by prefix (e.g., files starting with "log_")
• Text parsing or log filtering

Common Mistakes

• Assuming it's case-insensitive – use .lower() or .upper() to handle case.
• Passing an empty string – returns True because every string starts with "".

Interview Tip

In interviews, startswith() is often used in filtering, log analysis, and string-matching problems.

Summary

• startswith() checks if a string starts with a given prefix.
• Supports optional start and end positions.
• Returns True or False.
• Is case-sensitive.

Practice Problem

Write a program that reads a filename from the user and checks if it starts with "img_".

filename = input("Enter filename: ")
if filename.startswith("img_"):
    print("This is an image file.")
else:
    print("Not an image file.")