[issue21560] gzip.write changes trailer ISIZE field before type checking - corrupted gz file after trying to write string

[Claudiu.Popa]

Claudiu.Popa added the comment:

Moving `self.crc = zlib.crc32(data, self.crc) & 0xffffffff` before `self.size = self.size + len(data)` should be enough. Also, your patch needs a test.

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nosy: +Claudiu.Popa

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<http://bugs.python.org/issue21560>
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