Getting copy of lists or objects in python

equality_creates_reference.py

>>> a = ["a","b","c"]
>>> b = a
>>> b.append("d")
>>> print a, b
['a', 'b', 'c', 'd'] ['a', 'b', 'c', 'd']

equality_creates_reference_2.py

>> class obj:
...     def __init__(self):
...         self.counter = 0
...     def inc(self):
...         self.counter += 1
... 

>>> a = obj()
>>> b = a
>>> a.inc()
>>> print a.counter
1
>>> print b.counter
1

getting_real_copy_of_lists.py

>>> a = ["a","b","c"]
>>> b = list(a)
>>> print a , b
['a', 'b', 'c'] ['a', 'b', 'c']
>>> a.append("d")
>>> print a, b
['a', 'b', 'c', 'd'] ['a', 'b', 'c']

getting_real_copy_of_object.py

>>> class obj:
...     def __init__(self):
...         self.counter = 0
...     def inc(self):
...         self.counter += 1
... 

>>> a = obj()
>>> from copy import copy
>>> b = copy(a)
>>> a.inc()
>>> b.inc()
>>> b.inc()
>>> b.inc()
>>> print a.counter, b.counter
1 3

official method of copying list.py

>>> a = [1,2,3]
>>> b = a[:]
>>> b.append(3)
>>> b
[1, 2, 3, 3]
>>> a
[1, 2, 3]