A Comprehensive Guide to Using `startswith()` and `endswith()` in Python

Python offers a wide range of built-in functions and methods that make string manipulation a breeze. Among these, the `startswith()` and `endswith()` methods are valuable tools for checking the beginnings and endings of strings, respectively. In this article, we will explore how to use these methods with practical examples.

1. Introduction to `startswith()` and `endswith()`.

1. Both `startswith()` and `endswith()` are string methods in Python used to determine if a given string starts or ends with a specified prefix or suffix, respectively.
2. They return a Boolean value (True or False) based on the outcome of the check.
3. These methods are commonly used for data validation, filtering, and conditional branching.

1.1 The `startswith()` Method.

1. The `startswith()` method checks whether a string begins with a specified substring. Its syntax is as follows:

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

2. `string`: The string you want to check.
3. `prefix`: The substring you want to search for at the beginning of the string.
4. `start` (optional): The starting index for the search. If provided, the search will begin at this index.
5. `end` (optional): The ending index for the search. If provided, the search will stop before this index.

1.2 The `endswith()` Method.

1. The `endswith()` method, on the other hand, checks whether a string ends with a specified substring. Its syntax is similar to `startswith()`:

   string.endswith(suffix[, start[, end]])

2. `string`: The string you want to check.
3. `suffix`: The substring you want to search for at the end of the string.
4. `start` (optional): The starting index for the search. If provided, the search will begin at this index.
5. `end` (optional): The ending index for the search. If provided, the search will stop before this index.

2. Using `startswith()` with Examples.

1. Let’s start by exploring the `startswith()` method with some practical examples:

2.1 Example 1: Basic Usage.

1. Source code.

   text = "Hello, World!"
   result = text.startswith("Hello")
   print(result)  # Output: True

2. In this example, the `startswith()` method checks if the string text starts with the substring “Hello“. Since it does, the method returns `True`.

2.2 Example 2: Specifying Start and End.

1. You can specify the start and end positions for the search:

   >>> text = "Python is great!"
   >>> result = text.startswith("is", 7, 13)
   >>> print(result)  # Output: True
   True
   >>>
   #>>> result = text.startswith("is", 6, 13)
   #>>> print(result)  # Output: False
   #False

2. Here, we check if the substring “is” starts at index 7 and ends before index 13 in the string. Since it does, the method returns `True`.

2.3 Example 3: Checking for Multiple Prefixes.

1. You can check if a string starts with any of several prefixes using a tuple:

   >>> text = "apple banana cherry"
   >>> prefixes = ("apple", "orange", "banana")
   >>> result = text.startswith(prefixes)
   >>> print(result)  # Output: True
   True
   >>>
   >>> prefixes = ( "orange", "banana")
   >>>
   >>> result = text.startswith(prefixes)
   >>>
   >>> print(result)  # Output: False
   False

2. In this case, the method returns `True` because the string starts with one of the prefixes in the tuple.

3. Using `endswith()` with Examples.

1. Now, let’s dive into the `endswith()` method with some illustrative examples:

3.1 Example 1: Basic Usage.

1. Source code.

   filename = "document.pdf"
   result = filename.endswith(".pdf")
   print(result)  # Output: True

2. In this example, we check if the filename ends with the suffix “.pdf“. Since it does, the method returns `True`.

3.2 Example 2: Specifying Start and End.

1. You can also specify the start and end positions for the search, similar to `startswith()`:

   >>> text = "Python is great!"
   >>> result = text.endswith("is", 0, 10)
   >>> print(result)  # Output: False
   False
   >>> result = text.endswith("is", 0, 9)
   >>> print(result)  # Output: True
   True

2. Here, we check if the substring “is” ends at index 10 in the string. Since it does not, the method returns `False`.

3.3 Example 3: Checking for Multiple Suffixes.

1. Just like with `startswith()`, you can check if a string ends with any of several suffixes using a tuple:

   >>> filename = "document.pdf"
   >>> suffixes = (".pdf", ".txt", ".doc")
   >>> result = filename.endswith(suffixes)
   >>> print(result)  # Output: True
   True

2. The method returns True because the filename ends with one of the suffixes in the tuple.

4. Conclusion.

1. In this article, we have explored how to use the `startswith()` and `endswith()` methods in Python for checking prefixes and suffixes in strings.
2. These methods are valuable tools for performing string validation, filtering, and conditional logic.
3. By mastering these techniques, you can efficiently manipulate strings and enhance the functionality of your Python programs.