Python variables changing when they shouldn't

Question

The code that I am working on is changing my temporary variables, and I can't figure out how to stop it. Essentially, this is the problem:

def example(array):
    temp = array
    for i in range whatever:
        #change array

I need to change array, but keep temp the same.

You usually only need the copy module if you need a generic copying function to copy objects independent of their type. — Sven Marnach
– Sven Marnach, Commented Jul 6, 2012 at 12:35

Sven Marnach · Accepted Answer · 2012-07-06 12:31:06Z

6

The line

temp = array

does not copy the contents of array – it simply binds another name to the same object. How to actually copy an object depends on the type of the object. For a NumPy array, you can do

temp = array.copy()

For a Python list, you can use the above line starting from Python 3.3; in eariler version, you can use

temp = array[:]

There are also the generic copying functions copy() and deepcopy() in the module copy.

answered Jul 6, 2012 at 12:31

Sven Marnach

608k123 gold badges969 silver badges866 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

marcinx27 Over a year ago

I tried both of these options, and neither seems to work. temp continues to change.

marcinx27 Over a year ago

Nevermind. I'm just an idiot and skipped over the 'deepcopy()' suggestion. It worked perfectly. A million, billion thanks.

Eric O. Lebigot · Accepted Answer · 2012-07-06 12:31:21Z

1

temp = array only indicates that temp is another name for the contents of the array variable.

In general, if you want a copy, you can use the copy module and do:

import copy

temp = copy.copy(arr)  # or copy.deepcopy(arr), depending on the situation

answered Jul 6, 2012 at 12:31

Eric O. Lebigot

95.1k49 gold badges224 silver badges263 bronze badges

Collectives™ on Stack Overflow

Python variables changing when they shouldn't

2 Answers 2

2 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related