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Packing and unpacking are terms used to describe the process of transforming data between representations, typically to save space, enable transmission, or permit processing. Packing refers to assembling multiple values or fields into a single, compact form such as a byte sequence, memory block, or structured record. Unpacking is the reverse operation, extracting the original components from that form.

In data serialization and binary protocols, packing converts high-level values into a sequence of bytes. Unpacking reverses this to recover the original values. Endianness, alignment, and padding affect how data are packed, and correct unpacking requires matching the packing format precisely.

Programming languages use packing and unpacking in different ways. For example, Python provides facilities for packing and unpacking binary data via the struct module, which converts between Python values and C-style bytes according to a format string. Python also uses argument packing and unpacking with *args and **kwargs when calling functions. In languages like C or C++, packing may be influenced by memory layout, bit-fields, and compiler-specific attributes that control how structures are stored in memory.

In networked and storage contexts, packing reduces bandwidth and space by encoding data compactly, while unpacking decodes received messages or stored data back into usable values. Explicit packing routines are common in messaging systems, RPC frameworks, and file formats to ensure consistent interpretation across different machines or platforms.

Overall, packing and unpacking describe the dual operations of assembling data into a transferable form and restoring it to its constituent parts, across a range of computing contexts.