Creating Python variables independent of each other

Question

If I have this Python code:

foo = [3, 5, 9]
bar = foo
bar.append(9)
print(foo)

He returns

[3, 5, 9, 9]

This, of course, means that when added 9to barit also affected foo. How to make a variable barequal foo, but so that when I edit barit does not affect foo?

Answer 1

You are modifying the mutable value, so you need to make an explicit copy:

bar = list(foo)

or

bar = foo[:]

When assigning a name in Python, all you do is keep a reference to the value. Without creating a copy of the list, both fooand barbelong to the same list.

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Answer 2

:

bar = foo[:]  #copy of foo
bar.append(9)

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Answer 3

When creating copies of the original while deleting all references to it (so you cannot edit the original), you use a deep copy.

http://docs.python.org/2/library/copy.html

import copy
bar = copy.deepcopy(foo)

Answer 4

Use deepcopy:

>>> from copy import deepcopy
>>> foo = [3, 5, 9]
>>> bar = deepcopy(foo)
>>> bar.append(9)
>>> print(foo)
[3, 5, 9]
>>> print bar
[3, 5, 9, 9]