Description:

Problem:
I've encountered an issue with the Stream-Framework library's ActivitySerializer class when using the Pickle protocol 4. The serialization process seems to fail when the serialized data contains a semicolon character, which leads to unexpected behavior.

Code Sample:

def dumps(self, activity):
    self.check_type(activity)
    activity_time = '%.6f' % datetime_to_epoch(activity.time)
    parts = [activity.actor_id, activity.verb.id,
             activity.object_id, activity.target_id or 0]
    extra_context = activity.extra_context.copy()
    pickle_string = ''
    if extra_context:
        pickle_string = pickle.dumps(activity.extra_context)
        if six.PY3:
            pickle_string = pickle_string.decode('latin1')
    parts += [activity_time, pickle_string]
    serialized_activity = ','.join(map(str, parts))
    return serialized_activity

Issue Details:
In the above code snippet, when using the Pickle protocol 4, if the activity.extra_context contains a semicolon character, the serialization process breaks. This appears to be due to changes in the Pickle module's behavior between protocol versions 3 and 4.

Steps to Reproduce:

if we do this we get semicolon
pickle.dumps({'actor_type': 'brand', 'description': 'Some Description'})
output:  b'\x80\x04\x95;\x00\x00\x00\x00\x00\x00\x00}\x94(\x8c\nactor_type\x94\x8c\x05brand\x94\x8c\x0bdescription\x94\x8c\x10Some Description\x94u.'

But if we do use protocol 3 then no semicolon

pickle.dumps({'actor_type': 'brand', 'description': 'Some Description'}, protocol=3)
output: b'\x80\x03}q\x00(X\n\x00\x00\x00actor_typeq\x01X\x05\x00\x00\x00brandq\x02X\x0b\x00\x00\x00descriptionq\x03X\x10\x00\x00\x00Some Descriptionq\x04u.'