pip/pip/utils/encoding.py

import codecs
import locale
import re


BOMS = [
    (codecs.BOM_UTF8, 'utf8'),
    (codecs.BOM_UTF16, 'utf16'),
    (codecs.BOM_UTF16_BE, 'utf16-be'),
    (codecs.BOM_UTF16_LE, 'utf16-le'),
    (codecs.BOM_UTF32, 'utf32'),
    (codecs.BOM_UTF32_BE, 'utf32-be'),
    (codecs.BOM_UTF32_LE, 'utf32-le'),
]

ENCODING_RE = re.compile('coding[:=]\s*([-\w.]+)')


def auto_decode(data):
    """Check a bytes string for a BOM to correctly detect the encoding

    Fallback to locale.getpreferredencoding(False) like open() on Python3"""
    for bom, encoding in BOMS:
        if data.startswith(bom):
            return data[len(bom):].decode(encoding)
    # Lets check the first two lines as in PEP263
    for line in data.splitlines()[:2]:
        if line.startswith('#') and ENCODING_RE.search(line):
            encoding = ENCODING_RE.search(line).groups()[0]
            return data.decode(encoding)
    return data.decode(locale.getpreferredencoding(False))