confusion about variable scope in a class

[gyro]

Hi,
I was writing a Python script to perform some data analyses and was
surprised by some behavior I noted. A simple test program illustrating
the behavior is below.
I do not understand why the value of 'data' is being modified. I am
obviously missing something obvious, and would certainly appreciate an
explanation of why this is happening.

Thank you.

-gf

----------

#!/bin/env python

class TestPop(object):
    def round1(self,data1):
        t = data1.pop(-1)
		
    def round2(self,data2):
        t = data2.pop(-1)
		
    def tester(self):
        data = range(10)
        self.round1(data)
        print data
        self.round2(data)
        print data

if __name__ == '__main__':
    tp = TestPop()
    tp.tester()