Perform random-access read and write operations on a file descriptor using pread and pwrite.

Illustrate how to perform efficient, offset-specific I/O operations without changing the file pointer.

When needing to read or write data at specific file offsets concurrently or without altering the current file offset, such as in packet processing, database page access, or binary file patching.

Systems programming, binary file manipulation, database storage engines, network packet logging, any scenario requiring concurrent read/write at fixed offsets.

os.open(path, flags) -> fd; buf = bytearray(size); os.pread(fd, buf, offset); os.pwrite(fd, data, offset); os.close(fd)

1. Open file descriptor with os.open; 2. Allocate mutable buffer; 3. Read data at specific offset via os.pread; 4. Write data at specific offset via os.pwrite; 5. Close file descriptor.

{path}: file path string; {flags}: file opening flags (e.g., os.O_RDWR); {buf_size}: size of bytearray buffer; {read_offset}: offset for pread; {write_data}: bytes-like object to write; {write_offset}: offset for pwrite

• os.open
• os.O_RDWR
• bytearray
• os.pread
• os.pwrite
• os.close
• offset
• offset
• bytes

• Different flags (os.O_RDONLY
• os.O_WRONLY|os.O_CREAT)
• different buffer sizes
• using memoryview instead of bytearray
• using os.read/os.write with lseek
• using mmap for frequent random access.

Failing to close the file descriptor leading to resource leaks; passing a string instead of a bytes-like object to os.pwrite; miscalculating offsets causing reads/writes beyond file size; ignoring return values which indicate number of bytes transferred; assuming pread/pwrite update the file offset (they do not).

Using built-in open() with seek()/read()/write() to achieve the same result but altering the file pointer; employing mmap for frequent random access may be more efficient than repeated pread/pwrite calls.

Confusing pread/pwrite with regular read/write which modify the file offset, leading to unexpected file pointer positions; mixing pread/pwrite with lseek calls can cause confusion about the actual file position.

• file-io-lowlevel

pread and pwrite perform the read/write operation atomically with respect to other processes and do not change the file offset, enabling safe concurrent access to the same file descriptor from multiple threads or processes.

Shows how to perform efficient, offset-specific I/O without side effects on the file pointer, suitable for concurrent or random-access file patterns.

Think 'pread/pwrite' for offset‑specific I/O that leaves the file pointer untouched.

Example uses a fixed 512‑byte buffer and writes a 64‑byte repeated pattern at offset 2048; adjust sizes and offsets as needed for your use case.

Consider using mmap for frequent random reads/writes, or higher‑level io.BufferedRandom with seek for simpler code; for vectorized I/O, look into os.preadv/os.pwritev where available.