How to create variable names with a "for" loop?

Question

I know my title may be somewhat confusing, but I had trouble describing my issue. Basically, I need to create a bunch of variables that all equal 0, and I want to do this with a for loop so I don't have to hard code it.

The problem is each variable needs to have a different name and when I call the number from my for loop to create the variable, it doesn't recognize that I want the number from the for loop. Here is some code so that makes more sense:

total_squares = 8
box_list = []
for q in range(total_squares):
  box_q = 0
  box_list.append(box_q)

I need it to create box_1 and add that to the list, then create box_2, and add that to the list. Just it thinks I'm calling a variable box_q, rather than calling the number in the for loop.

Why don't you use a list instead of a variable number of variables? You can have a list of lists, e.g. `box_list[box[3]]` — Selcuk, Nov 27 '18 at 23:49
You must manipulate the `globals()` dictionary for this (it doesn't work for function local variables). Anyway, using a list or dict directly would be much better, as @Selcuk already said. — Michael Butscher, Nov 27 '18 at 23:51
See [Why you don't want to dynamically create variables](http://stupidpythonideas.blogspot.com/2013/05/why-you-dont-want-to-dynamically-create.html) and the related [Keep data out of your variable names](https://nedbatchelder.com/blog/201112/keep_data_out_of_your_variable_names.html). — martineau, Nov 28 '18 at 00:02

score 2 · Answer 1 · 2018-11-28T00:08:42.850

2

You can use dictionary. This approach is better in my opinion as you can see the the key and value pair.

code

total_squares=8
box_list={}
for q in range(total_squares):
    box_list['box_'+str(q)]=0

print(box_list)

output

{'box_0': 0, 'box_1': 0, 'box_2': 0, 'box_3': 0, 'box_4': 0, 'box_5': 0, 'box_6': 0, 'box_7': 0}

edited Nov 28 '18 at 00:08

answered Nov 28 '18 at 00:00

Why was this answer downvoted? – Nov 28 '18 at 00:33

Selcuk · Accepted Answer · 2018-11-27T23:59:27.640

1

Creating variables dynamically is an anti-pattern and should be avoided. What you need is actually a list:

total_squares = 8
box_list = []
boxes = [0] * total_squares
for q in range(total_squares):
  box_list.append(boxes[q])

Then you can refer to any element you want (say, box_i) using the following syntax:

my_box = box_list[boxes[i]]

edited Nov 27 '18 at 23:59

answered Nov 27 '18 at 23:56

Selcuk

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1

Ah I understand. Thank you very much for taking time to explain it more for me! – Logan Holmes Nov 27 '18 at 23:59

score 1 · Answer 3 · answered Nov 28 '18 at 00:05

It looks like you're trying to use the value of q to edit the 'q' in box_q, but q and box_q are two completely different variables.

You can manipulate variable names dynamically, but this is very rarely done in Python. Good explanation here: https://nedbatchelder.com/blog/201112/keep_data_out_of_your_variable_names.html

Instead, you can use a list and access the items using list indexing, e.g.

total_squares = 8
box_list = []
for q in range(total_squares):
    box_list.append(0)

You access each item with box_list[0], box_list[1], etc. You can also create your boxes more succinctly:

boxes = [0] * total_squares

If you want your boxes to contain something, and have this naming structure, then you could use a dictionary:

boxes_dict = {'box_{}'.format(q): 0 for q in range(total_squares)}

This creates a dictionary with total_squares key-value pairs. You can access each box using boxes_dict['box_0'], boxes_dict['box_1'], etc. You can even change the values from 0 to put something in the box, e.g.

boxes_dict['box_2'] = "Don't use dynamic variable naming"
boxes_dict['box_3'] = 'And number your boxes 0, 1, 2 ... etc'

How to create variable names with a "for" loop?

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