Python File Handling

Python File Handling: Context Managers & Open Modes

File I/O in Python should always use context managers (with open(...) as file:) to guarantee automatic file handle closure even if exceptions occur.

Open Access Modes Table

Practical Code Example

from pathlib import Path

def file_io_demo(file_path: Path) -> None:
    # Writing text cleanly via Context Manager
    with open(file_path, mode='w', encoding='utf-8') as f:
        f.write("Line 1: Log Entry
")
        f.write("Line 2: System Status OK
")

    # Appending text
    with open(file_path, mode='a', encoding='utf-8') as f:
        f.write("Line 3: Appended Audit Record
")

    # Reading contents
    with open(file_path, mode='r', encoding='utf-8') as f:
        content = f.read()

    print("--- File Contents ---")
    print(content)

if __name__ == "__main__":
    target = Path("sample_test_file.txt")
    file_io_demo(target)
    if target.exists():
        target.unlink()  # Cleanup

Best Practices & Gotchas

• Always Specify Encoding: Always pass encoding='utf-8' explicitly when opening text files to prevent platform-dependent default encoding bugs.
• Always Use with Statement: Never call f = open(...) without a context manager; unclosed file handles cause resource leaks.
• Use 'x' for Safe Writing: Use mode 'x' when creating new files to prevent accidentally overwriting an existing file.

Self-Check Challenge

Write a context manager block that writes three lines to test.log and reads them back.