You’ll be able to
- Read and write files with
open()context managers - Handle text vs binary modes correctly
- Parse structured text like CSV without external libraries
- Understand encoding gotchas: UTF-8 vs ASCII
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Why this matters
io.StringIO and io.BytesIO let code that expects a file object (pandas read_csv, csv.writer, PIL.Image.open) work with in-memory data — critical for unit tests and Lambda handlers where the filesystem is read-only or ephemeral.
Common pitfalls
- Forgetting to
seek(0)after writing — the read pointer is at the end; you'll get an empty string back. - Mixing
StringIO(text) with binary APIs likepickle.dump— useBytesIOfor anything non-text. - Not closing buffers in long-running processes — wrap in
with io.StringIO() as buf:to free memory.