int() ignores everything after a null byte when reporting an error message.

Here you can see an example of how this manifests, and why could be a problem.

Python 2.7.6 (default, Nov 10 2013, 19:24:18) [MSC v.1500 32 bit(Intel)] on win32
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>>> int('a')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: invalid literal for int() with base 10: 'a'
>>> int('\0a')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: invalid literal for int() with base 10: ''
>>> int('abc\0def')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: invalid literal for int() with base 10: 'abc'