<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_nvr(self, epoch=None):
 """get NVR string from .spec Name, Version, Release and Epoch"""

        name = self.get_tag('Name', expand_macros=True)
        vr = self.get_vr(epoch=epoch)
        return '%s-%s' % (name, vr)