all Python 3structfunction

struct.pack()

packing and unpacking

Packs values into bytes according to a struct format string: numbers, byte strings, flags — in a chosen byte order.

Syntax

data = struct.pack(format, v1, v2, ...)

Without a '<', '>' or '!' prefix the byte order and padding come from the current machine and the result is not portable. A value out of range for its code is struct.error, not silent truncation: 300 does not fit 'B'. The 's' code accepts only bytes, not str, and silently pads with zeros or truncates to the given length.

Examples

import struct
print(struct.pack('>I', 1))  # → b'\x00\x00\x00\x01'
print(struct.pack('<I', 1))  # → b'\x01\x00\x00\x00'
print(struct.pack('<5s', b'abc'))  # → b'abc\x00\x00'

import struct
try:
    struct.pack('<B', 300)
except struct.error as e:
    print(e)  # → format requires 0 <= number <= 255

See also

Common errors

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