Python int to hex string

class crc32calc:
    def __init__(self): self.value = 0
    def update(self, data): self.value = zlib.crc32(data, self.value)
    def digest(self): return self.value
    def hexdigest(self): return '%08x' % self.value

Trying to get result of crc32 sum in hex. '%08x', however, sometimes returns a negative value (negative sign followed by seven hex digits). How can I get the right value?

Is Python tail-recursive?