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compiled regex objects' match method offers an optional "pos" parameter described to be roughly equivalent to slicing except for how it treats the "^" operation. See http://docs.python.org/library/re.html#re.RegexObject.search
However, the behavior of lookbehind assertions also differs:
>>> re.compile("(?<=a)b").match("ab", 1)
<_sre.SRE_Match object at 0x...>
>>> re.compile("(?<=a)b").match("ab"[1:])
>>>
This alone might be a documentation bug, but the behavior is also inconsistent with the behavior of lookahead assertions, which do *not* look past the endpos:
>>> re.compile("a(?=b)").match("ab", 0, 1)
>>> re.compile("a(?=b)").match("ab")
<_sre.SRE_Match object at 0x...>
>>>