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Lib/binascii.py

Source:

cpython 3.14 @ ab2d84fe1023/Modules/binascii.c

binascii is implemented entirely in C (Modules/binascii.c). There is no Lib/binascii.py. It provides the low-level binary-to-ASCII conversion primitives used by base64, uu, quopri, and email.base64mime.

Map​

SymbolRole
b2a_base64(data)Encode bytes to Base64 with a trailing newline
a2b_base64(ascii)Decode Base64 bytes
b2a_hex(data) / hexlifyEncode to hex string
a2b_hex(ascii) / unhexlifyDecode from hex string
b2a_uu(data)UUencode a 45-byte chunk
a2b_uu(ascii)Decode a UUencoded line
b2a_qp(data)Quoted-Printable encode
a2b_qp(ascii)Quoted-Printable decode
crc32(data, value=0)CRC-32 checksum
crc_hqx(data, value)CRC-CCITT (binhex) checksum

Reading​

b2a_base64​

// CPython: Modules/binascii.c binascii_b2a_base64_impl
static PyObject *
binascii_b2a_base64_impl(PyObject *module, Py_buffer *data, int newline)
{
    ...
    /* 3 bytes -> 4 base64 chars, rounded up, plus optional newline */
    ...
    while (p < e) {
        *q++ = table_b2a_base64[(*p >> 2) & 0x3f];
        *q++ = table_b2a_base64[((*p << 4) | ((p[1] >> 4) & 0xf)) & 0x3f];
        *q++ = table_b2a_base64[((p[1] << 2) | ((p[2] >> 6) & 3)) & 0x3f];
        *q++ = table_b2a_base64[p[2] & 0x3f];
        p += 3;
    }
    ...
}

Uses a 64-entry lookup table table_b2a_base64 for the encoding step.

crc32​

Computes the CRC-32 checksum using the standard polynomial 0xEDB88320. The value parameter is the running CRC; successive calls can chain over multiple buffers.

// CPython: Modules/binascii.c binascii_crc32_impl
static PyObject *
binascii_crc32_impl(PyObject *module, Py_buffer *data, unsigned int value)
{
    ...
    unsigned int crc = value ^ 0xFFFFFFFF;
    for (Py_ssize_t i = 0; i < data->len; i++) {
        crc = crc_table[(crc ^ buf[i]) & 0xff] ^ (crc >> 8);
    }
    return PyLong_FromUnsignedLong((crc ^ 0xFFFFFFFF) & 0xffffffff);
}

hexlify / unhexlify​

hexlify(data) returns a bytes object with each byte encoded as two lowercase hex digits. unhexlify(hex) decodes it. Both are O(n) single-pass operations.

gopy notes​

Status: partially covered. crc32 maps to hash/crc32.ChecksumIEEE. hexlify/unhexlify map to encoding/hex.EncodeToString/DecodeString. b2a_base64 / a2b_base64 are internal details of base64; the gopy base64 module would call Go's encoding/base64 directly rather than going through a binascii layer.