File I/O manipulation

Reset the file cursor to the start of the file for reading or rewriting.

After writing data to a file and needing to read it back; when reusing a file object for multiple passes; before processing a file again in a loop.

Any code that opens files with built-in open() or io objects such as BytesIO, especially in read-write modes.

file_obj.seek(offset)

... .seek(... )

file_obj: an open file-like object supporting seek (e.g., file, BytesIO); offset: integer position (0 for start).

• open()
• with statement
• tell()
• read()
• write()

• file_obj.seek(0
• os.SEEK_SET) (explicit whence)
• file_obj.seek(0
• 0)

Forgetting to flush before seeking in write mode; using seek on a closed file; assuming seek works on text files opened in binary mode incorrectly.

file_obj.tell() (returns current position); file_obj.truncate() (resizes file); seeking to end with seek(0, os.SEEK_END).

Coming from C: may assume seek offset is always in bytes — in Python text mode the offset is in decoded characters, use binary mode ('rb') for byte‑accurate positioning.

• f.tell
• f.truncate
• file.read
• file.write

Do not use f.seek on text files opened in text mode when you need byte‑precise positioning; seeking can be expensive on buffered or compressed streams as it may require buffering or decompression; seeking past the current file size extends the file with undefined bytes (zeros in binary mode) which can create sparse files.

Enables efficient random access to large files without loading them entirely into memory, making tasks like log parsing, binary parsing, and partial file updates feasible.

Think of f.seek as moving a bookmark in a book to jump directly to any page without reading the pages in between.

In text mode, the offset is interpreted as UTF-8 decoded characters; open the file in binary mode ('rb') for byte-accurate seeks.

f.seek(offset, whence) with os.SEEK_SET / os.SEEK_CUR / os.SEEK_END for relative positioning; mmap for memory-mapped random file access