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Python File Modes (r, w, a, x)

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In Python, file modes determine how a file is opened and interacted with. Choosing the correct mode is crucial for reading, writing, appending, or creating files safely. Each mode has a specific behavior that impacts data preservation and program execution.

This tutorial covers all file modes, their usage, practical examples, and best practices for efficient file handling.

What Are File Modes?

When you open a file in Python using the open() function, you must specify the mode. The mode defines whether the file is:

  • Opened for reading

  • Opened for writing

  • Opened for appending

  • Created only if it doesn’t exist

Syntax:

file = open("filename", "mode")

  • filename – Name of the file

  • mode – File mode ('r', 'w', 'a', 'x', etc.)

Mode: 'r' – Read Mode

  • Default mode if no mode is specified

  • Opens the file for reading only

  • Raises FileNotFoundError if the file does not exist

Example:

file = open("example.txt", "r")
content = file.read()
print(content)
file.close()

  • Use 'r' when you only need to access file content

  • Does not allow writing or modifying the file

Mode: 'w' – Write Mode

  • Opens the file for writing

  • If the file exists, its contents are overwritten

  • If the file does not exist, a new file is created

Example:

file = open("example.txt", "w")
file.write("Python file handling in write mode.\n")
file.close()

  • Use 'w' to create new files or overwrite existing files

  • Important: Existing data will be lost

Mode: 'a' – Append Mode

  • Opens the file for appending

  • New data is added to the end of the file

  • Does not overwrite existing content

  • Creates a new file if it does not exist

Example:

file = open("example.txt", "a")
file.write("This line will be appended.\n")
file.close()

  • Ideal for logs, records, or incremental data storage

  • Ensures existing data is preserved

Mode: 'x' – Create Mode

  • Opens the file for exclusive creation

  • Creates a new file only if it does not exist

  • Raises FileExistsError if the file already exists

Example:

file = open("newfile.txt", "x")
file.write("This file is created using 'x' mode.\n")
file.close()

  • Use 'x' to prevent overwriting important files

  • Useful in automation scripts where accidental overwriting must be avoided

Binary Modes

Python also supports binary file modes for non-text files like images or PDFs:

Mode Description
rb Read binary
wb Write binary
ab Append binary
xb Create binary

Example: Writing binary data:

data = b"Binary data example."
with open("example.bin", "wb") as file:
    file.write(data)

Text vs Binary Modes

  • Text modes (r, w, a, x) – Work with strings

  • Binary modes (rb, wb, ab, xb) – Work with bytes

  • Use the appropriate mode depending on the file type

Using Context Managers

Using the with statement ensures files are automatically closed:

with open("example.txt", "w") as file:
    file.write("File handling with context manager.\n")

  • Prevents resource leaks

  • Recommended for all file operations

Summary of File Modes

Mode Purpose Behavior
r Read Access file content, error if file does not exist
w Write Overwrites existing content, creates file if not exists
a Append Adds data to the end, preserves existing content
x Create Creates a new file, error if file exists
rb Read binary Reads bytes from a file
wb Write binary Writes bytes to a file, overwrites existing file
ab Append binary Adds bytes at the end of the file
xb Create binary Creates new binary file, error if exists

Practical Examples

  1. Read a file using 'r' mode:

with open("example.txt", "r") as file:
    print(file.read())

  1. Write a file using 'w' mode:

with open("example.txt", "w") as file:
    file.write("This is written in write mode.\n")

  1. Append text using 'a' mode:

with open("example.txt", "a") as file:
    file.write("Appending new text.\n")

  1. Create a new file using 'x' mode:

with open("newfile.txt", "x") as file:
    file.write("File created using 'x' mode.\n")

  1. Write binary data using 'wb':

data = b"Example binary data"
with open("data.bin", "wb") as file:
    file.write(data)

  1. Read binary file using 'rb':

with open("data.bin", "rb") as file:
    content = file.read()
    print(content)

  1. Append binary data using 'ab':

data = b"\nAdditional bytes"
with open("data.bin", "ab") as file:
    file.write(data)

  1. Prevent overwriting using 'x' mode:

try:
    with open("example.txt", "x") as file:
        file.write("Safe creation.\n")
except FileExistsError:
    print("File already exists!")

  1. Iterate over a file opened in 'r' mode:

with open("example.txt", "r") as file:
    for line in file:
        print(line.strip())

  1. Writing multiple lines safely:

lines = ["Line 1\n", "Line 2\n"]
with open("example.txt", "w") as file:
    file.writelines(lines)

Summary of the Tutorial

Python file modes determine how files are opened and manipulated:

  • r – Read only

  • w – Write, overwrites if file exists

  • a – Append, preserves content

  • x – Create exclusively, error if exists

Binary modes handle non-text data like images or PDFs. Always use context managers (with) to ensure safe opening and closing of files.

Mastering file modes is essential for data management, automation, and safe file operations, forming the foundation of real-world Python applications.

Practice Questions

Q1. Write a Python program to open a file in read ("r") mode and print its content.

Q2. Write a Python program to write "Good Morning" to a file using "w" mode (overwrites existing content).

Q3. Write a Python program to append a message to a file using "a" mode without deleting previous content.

Q4. Write a Python program to create a file using "x" mode and add some text (error if file already exists).

Q5. Write a Python program to handle error if a file does not exist in "r" mode using try-except.

Q6. Write a Python program to use "wb" mode to write binary data like b'010101' to a file.

Q7. Write a Python program to open a text file using "rt" mode and read its content.

Q8. Write a Python program to try opening a non-existing file in "x" mode and handle the error.

Q9. Write a Python program to check what happens if "w" mode is used on an existing file (observe overwritten content).

Q10. Write a Python program to read image data using "rb" mode and print the type of the data (should be bytes).

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