<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def build_number(self):
 """Swimlane build number"""

        version_separator = '+'
        if version_separator in self.version:
            # Post product/build version separation
            return self.version.split(version_separator)[2]
        # Pre product/build version separation
        return self.version.split('-')[1]