foo.py

class example:
    def __init__(self):
        self.name = 'dummy example'
    def bigNumber(self, number):
        return number * 1000000000
e = example()
e.name # 'dummy example'
e.bigNumber(5) # 5000000000
print('{:_}'.format(e.bigNumber(5))) # 5_000_000_000