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import re
ASCII_IS_DEFAULT_ENCODING = False
cookie_re = re.compile(r"^[ \t\f]*#.*coding[:=][ \t]*[-\w.]+")
BOM_UTF8 = '\xef\xbb\xbf'
def _prepare_source(fn):
"""Read the source code for re-writing."""
try:
stat = fn.stat()
source = fn.read("rb")
except EnvironmentError:
return None, None
if ASCII_IS_DEFAULT_ENCODING:
# ASCII is the default encoding in Python 2. Without a coding
# declaration, Python 2 will complain about any bytes in the file
# outside the ASCII range. Sadly, this behavior does not extend to
# compile() or ast.parse(), which prefer to interpret the bytes as
# latin-1. (At least they properly handle explicit coding cookies.) To
# preserve this error behavior, we could force ast.parse() to use ASCII
# as the encoding by inserting a coding cookie. Unfortunately, that
# messes up line numbers. Thus, we have to check ourselves if anything
# is outside the ASCII range in the case no encoding is explicitly
# declared. For more context, see issue #269. Yay for Python 3 which
# gets this right.
end1 = source.find("\n")
end2 = source.find("\n", end1 + 1)
if (not source.startswith(BOM_UTF8) and
cookie_re.match(source[0:end1]) is None and
cookie_re.match(source[end1 + 1:end2]) is None):
try:
source.decode("ascii")
except UnicodeDecodeError:
# Let it fail in real import.
return None, None
# On Python versions which are not 2.7 and less than or equal to 3.1, the
# parser expects *nix newlines.
return stat, source
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