import codecs import locale import re import sys from typing import List, Tuple BOMS: List[Tuple[bytes, str]] = [ (codecs.BOM_UTF8, "utf-8"), (codecs.BOM_UTF16, "utf-16"), (codecs.BOM_UTF16_BE, "utf-16-be"), (codecs.BOM_UTF16_LE, "utf-16-le"), (codecs.BOM_UTF32, "utf-32"), (codecs.BOM_UTF32_BE, "utf-32-be"), (codecs.BOM_UTF32_LE, "utf-32-le"), ] ENCODING_RE = re.compile(rb"coding[:=]\s*([-\w.]+)") def auto_decode(data: bytes) -> str: """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.split(b"\n")[:2]: if line[0:1] == b"#" and ENCODING_RE.search(line): result = ENCODING_RE.search(line) assert result is not None encoding = result.groups()[0].decode("ascii") return data.decode(encoding) return data.decode( locale.getpreferredencoding(False) or sys.getdefaultencoding(), )