Writing Files in Python

Writing data to files is a core operation for data persistence, logging, and data export. Python offers simple and flexible methods to write text or binary data to files.

Key Concepts

Opening Files for Writing: Use 'w' mode to write (overwrites existing content), 'a' to append.
Writing Methods: write(), writelines().
Binary Writing: Use 'wb' mode for writing binary data.
File Auto-closing: Use with statement for safe file handling.
File Position: Writing starts at the beginning (overwrite) or end (append) depending on mode.

10 Python Examples for Writing Files

Example 1: Writing a string to a file

with open('output.txt', 'w') as file:
    file.write("Hello, world!\n")

Example 2: Writing multiple lines using writelines()

lines = ["Line 1\n", "Line 2\n", "Line 3\n"]
with open('output.txt', 'w') as file:
    file.writelines(lines)

Example 3: Appending text to an existing file

with open('output.txt', 'a') as file:
    file.write("This line is appended.\n")

Example 4: Writing numbers as strings

numbers = [1, 2, 3, 4]
with open('numbers.txt', 'w') as file:
    for num in numbers:
        file.write(str(num) + '\\n')

Example 5: Writing with encoding specified

with open('utf8.txt', 'w', encoding='utf-8') as file:
    file.write("Some UTF-8 text: café\n")

Example 6: Writing binary data

with open('binaryfile.bin', 'wb') as file:
    data = bytes([120, 3, 255, 0])
    file.write(data)

Example 7: Writing formatted data using f-strings

name = "Alice"
score = 95
with open('results.txt', 'w') as file:
    file.write(f"{name} scored {score} points.\n")

Example 8: Using try-except with file writing

try:
    with open('output.txt', 'w') as file:
        file.write("Safe writing example\n")
except IOError as e:
    print("File write error:", e)

Example 9: Writing lines from user input

with open('user_input.txt', 'w') as file:
    for _ in range(3):
        line = input("Enter a line: ")
        file.write(line + '\\n')

Example 10: Overwriting a file with empty content

with open('output.txt', 'w') as file:
    pass  # this truncates the file, making it empty