File I/O

Persists in-memory data to a file on disk.

Data processing: saving transformed records to an output file. Logging: appending diagnostic messages to a log file. Scripting: generating a report file from computed results.

Scripts that process files, data pipelines, simple logging utilities.

file_object.write(data)

... .write(...)

file_object: file handle opened in write or append mode; data: string-like object to write (typically str).

• open() with 'w' or 'a' mode
• close() or with statement
• str() for non-string data.

• file_object.writelines(list_of_strings)
• print(...
• file=file_object).

Writing to a file opened in read mode (cause: misunderstanding mode strings) raises UnsupportedOperation (consequence: program crashes). Forgetting to convert non-string data to string (cause: assuming auto-coercion) raises TypeError (consequence: write fails). Not closing the file (cause: missing close() or with statement) leaves data in the buffer (consequence: data loss on crash).

file_object.read() for reading data; file_object.flush() to force buffer to disk.

Coming from Java: expecting write to immediately flush to disk without calling flush() → Python uses buffered I/O; rely on context managers to auto-flush and close.

• file open
• file read
• file close
• with statement
• file writelines

Do not use for structured data serialization (use json.dump or pickle.dump instead). Writing large strings can block the event loop in async contexts. Writing empty strings does nothing and does not truncate the file.

Ensures data is persisted to disk.

Think of a pen writing on paper: file.write() puts ink on the file.

For binary data, open file with 'b' flag and write bytes objects; ensure proper encoding when writing text.

Use a context manager with error handling: try: with open(path, 'w') as f: f.write(data) except IOError as e: handle_error(e)