Pybitcointools txhash function, and SIGHASH

pybitcointools has a txhash function which returns the singable form of a transaction, with SIGHASH appended.

However the code returns a reversed hash without the appended SIGHASH bytes for SIGHASH=None, as seen here: https://github.com/vbuterin/pybitcointools/blob/master/bitcoin/transaction.py#L177-L178

Code:

def txhash(tx, hashcode=None):
if isinstance(tx, str) and re.match('^[0-9a-fA-F]*$', tx):
tx = changebase(tx, 16, 256)
if hashcode:
return dbl_sha256(from_string_to_bytes(tx) + encode(int(hashcode), 256, 4)[::-1])
else:
return safe_hexlify(bin_dbl_sha256(tx)[::-1])

That doesn't seem right; is it?

Also, how is a SIGHASH_ALL value of zero (rare case) calculated? (See this related SE question)

Is it just changing the 00 to 01?