File I/O / Resource management

Ensures safe opening of paired input and output files for copying or transforming binary data.

File processing: copying files File processing: converting binary formats File processing: processing streams where data is read from a source and written to a destination

Standard Python scripts, data processing pipelines, file utilities, any binary file manipulation code.

with open(src_path, 'rb') as src_var, open(dst_path, 'wb') as dst_var:

with open(..., 'rb') as ..., open(..., 'wb') as ...:

src_path: str (path to source file), dst_path: str (path to destination file), src_var: file object for reading binary, dst_var: file object for writing binary

• read()
• write()
• shutil.copyfileobj()
• iter(chunks)
• hashlib hash updates

• Using 'r' and 'w' modes for text files
• pathlib.Path.open()
• separate nested with statements

Swapping 'rb' and 'wb' modes (confusing source and destination positions) → reads from output file or overwrites source with empty file; Using text mode 'r'/'w' instead of 'rb'/'wb' for binary data (assuming default mode is safe) → UnicodeDecodeError on read or corrupted output from newline translation; Opening the same path for both reading and writing in one with statement (expecting in-place edit) → 'wb' truncates the file before 'rb' can read it, yielding empty input

Nested with statements (with open(...) as f1: with open(...) as f2:), try/finally with manual close(), using contextlib.ExitStack for dynamic numbers of files

Coming from C: manual fopen/fclose management may lead to forgetting to close files. Coming from Java: try‑with‑resources is similar but syntax differs.

• file handling
• context managers
• resource acquisition is initialization (RAII)

Ensure binary mode ('rb'/'wb') when dealing with non‑text data; text mode may cause encoding issues or newline translation. For very large files, process in chunks rather than reading all at once.

Guarantees automatic resource cleanup, reduces boilerplate, and makes the intent of paired file handling explicit.

"Double open, double close – with handles both."

Use binary mode ('rb'/'wb') for binary data to avoid encoding issues; process large files in chunks to avoid excessive memory usage.

Using contextlib.ExitStack to handle a dynamic number of files: with ExitStack() as stack: files = [stack.enter_context(open(f, 'rb')) for f in inputs] outfile = stack.enter_context(open(output, 'wb')) ...