initial: add all custom Claude.ai skills

my-python-senior/files-io.md

@@ -0,0 +1,35 @@
+# Files, Streams, and Data Processing Guidelines
+
+## Basic principles
+
+- Prefer streaming and iterators over loading entire large files into memory.
+- Be explicit about encodings; default to UTF-8 when reasonable.
+- Use context managers for all resources (`with open(...) as f:`).
+
+## Large files and performance
+
+- For large text/binary files:
+  - process in chunks or line-by-line
+  - consider `mmap` for specific use cases where it simplifies access patterns.
+- Avoid unnecessary copies of large data structures.
+- For data processing, consider columnar formats (e.g. Parquet) when appropriate.
+
+## Safety and atomicity
+
+- For writes that must not corrupt data:
+  - write to a temporary file
+  - fsync if necessary
+  - then atomically rename.
+- Validate paths and avoid directory traversal vulnerabilities when working with user-supplied paths.
+- Handle missing directories gracefully (create them when sensible, or fail with a clear error).
+
+## Formats and parsing
+
+- Prefer standard libraries (`json`, `csv`, `pathlib`) where possible.
+- When using third-party libraries (e.g. `pyyaml`), use safe loading functions.
+- Clearly define schemas (via `pydantic` or dataclasses) when reading structured data.
+
+## Cross-platform behavior
+
+- Use `pathlib` instead of manual string path manipulation.
+- Be mindful of line endings, file permissions, and case sensitivity across OSes.