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()

 

[Diez B. Roggisch]

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.

Lists are mutables, and python passes around references to objects, not
copies.

So if you want a copy, you need to create one explicit, either by using e.g.


new_list = list(old_list)

which will create a shollow copy of the list, or by using the
library-module "copy" that also offers a "deepcopy" function.


Diez