[issue35557] Allow lowercase hexadecimal characters in base64.b16decode()

[Dylan Houlihan]

Change by Dylan Houlihan <dylan at breakingbits.net>:


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versions:  -Python 3.4, Python 3.5, Python 3.6, Python 3.7

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue35557>
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