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Python String startswith() Method – Check If a String Starts With


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.")


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