base64 is Python's module for providing various standard encoding functionalities, especially the eponymous base64. Little quirk about the decoding in Python 2.7, it ignores invalid characters!
>>> import base64
>>> test_str = base64.b64encode('123456789')
>>> base64.b64decode(test_str[:-4] + '....' + test_str[-4:])
'123456789'
>>> base64.b64decode(test_str[:-4] + '...' + test_str[-4:])
'123456789'
>>> base64.b64decode(test_str[:-4] + '.' + test_str[-4:])
'123456789'
>>> test_str[:-4]
'MTIzNDU2'
>>> base64.b64decode(test_str[:-4])
'123456'
Python 3 adds a flag, validate, but it's off by default. Oh well!
