There may be some file(3 bytes or 4 bytes or 5 bytes) zipped with some password(contains not only alphanumeric), may be it is better to support these conditions?
since I am not familiar with your code, maybe I could not give a pull request for now.

this crc32.py could solve 6 bytes crc32 value well,but couldn't solve 4 bytes value,how can do it by crc32.py?

This project should be packaged properly.

With a matrix and exponentiation by squaring, appending a block of data can be represented as an affine transformation, and the result of appending it N times to an existing hash can be computed in O(log N) time.

crc32_combine in zlib uses a linear transformation for appending zeroes to speed up combining CRC32 checksums. CRC(AB) = CRC(A0 ^ B0) = CRC(A0) ^ CRC(0B) = CRC(A0) ^ CRC(B) = M * CRC(A) ^ b. One zero byte needs to be appended to A for each zero byte in B, and then the checksums can be combined. This is an affine transformation with M as a matrix appending len(B) zero bytes (computed in O(log N) time as in crc32_combine) and b = CRC(B). Similarly, the affine transform that corresponds to applying that affine transform k times can be computed in O(log k) time. The total time complexity is O(log N + log k).

This would likely introduce a combine <c1> <c2> <len2> [n=1] command, which computes the effect of appending something with checksum c2 and length len2 to something with checksum c1 n times.