What is the difference between modes `a`, `a+`, `w`, `w+`, and `r+` in built-in file handling in Python?

Differences Between File Modes in Python File Handling

When working with files in Python, the mode you use determines how you can interact with the file. Here’s an explanation of the commonly used modes:

1. Mode a (Append)

• Opens the file for writing.
• Appends content to the end of the file without overwriting existing data.
• If the file doesn’t exist, it creates a new file.
• You cannot read from the file in this mode.

2. Mode a+ (Append and Read)

• Opens the file for both reading and appending.
• Appends content to the end of the file without overwriting existing data.
• Allows you to read the file as well as write to it.
• If the file doesn’t exist, it creates a new file.

3. Mode w (Write)

• Opens the file for writing.
• Overwrites the file if it already exists, erasing all previous data.
• If the file doesn’t exist, it creates a new file.
• You cannot read from the file in this mode.

4. Mode w+ (Write and Read)

• Opens the file for both reading and writing.
• Overwrites the file if it already exists, erasing all previous data.
• If the file doesn’t exist, it creates a new file.
• Allows you to both read from and write to the file.

5. Mode r+ (Read and Write)

• Opens the file for both reading and writing.
• The file pointer starts at the beginning of the file.
• Does not create a new file if it doesn’t exist.
• Overwriting happens from the start of the file, but it doesn’t truncate (erase) the file entirely unless explicitly done.

Quick Comparison Table

Key Notes:

• Use a or a+ when you want to preserve existing data and add new content to the end of the file.
• Use w or w+ when you want to start fresh with a file, erasing its content if it exists.
• Use r+ when you need to read and modify an existing file without erasing its content.