Using a loop in Python to name variables

Question

How do I use a loop to name variables? For example, if I wanted to have a variable double_1 = 2, double_2 = 4 all the the way to double_12 = 24, how would I write it?

I get the feeling it would be something like this:

for x in range(1, 13):
    double_x = x * 2 
    # I want the x in double_x to count up, e.g double_1, double_2, double_3

Obviously, this doesn't work, but what would be the correct syntax for implementing the looped number into the variable name? I haven't coded for a while, but I do remember there was a way to do this.

Solution 1

Use a dictionary instead. E.g:

doubles = dict()

for x in range(1, 13):
    doubles[x] = x * 2

Or if you absolutely must do this AND ONLY IF YOU FULLY UNDERSTAND WHAT YOU ARE DOING, you can assign to locals() as to a dictionary:

>>> for x in range(1, 13):
...     locals()['double_{0}'.format(x)] = x * 2
... 
>>> double_3
6

There never, ever should be a reason to do this, though - since you should be using the dictionary instead!

Solution 2

expanding my comment: "use a dict. it is exactly why they were created"

using defaultdict:

>>> from collections import defaultdict
>>> d = defaultdict(int)

using normal dict:

>>> d = {}

the rest:

>>> for x in range(1, 13):
    d['double_%02d' % x] = x * 2


>>> for key, value in sorted(d.items()):
    print key, value


double_01 2
double_02 4
double_03 6
double_04 8
double_05 10
double_06 12
double_07 14
double_08 16
double_09 18
double_10 20
double_11 22
double_12 24

Solution 3

Although I doubt you really need to do what you want, here's a way:

namespace = globals()
for x in range(1, 13):
    namespace['double_%d' % x] = x * 2

print double_1
print double_2
   ...
print double_12

globals() returns a dictionary representing the current global symbol table (the dictionary of the current module). As you can see, it's possible to add arbitrary entries to it.

Solution 4

As already mentioned, you should use a dict. Here's a nice easy way to create one that meets your requirements.

>>> {k:k*2 for k in range(1,13)}
{1: 2, 2: 4, 3: 6, 4: 8, 5: 10, 6: 12, 7: 14, 8: 16, 9: 18, 10: 20, 11: 22, 12: 24}

Solution 5

You can use the dict while it don't fit your requirement. But I hope it can help you.

var_dic = {}
for x in range(1, 13):
    var_dic["double_%s"% str(x)] = x * 2
print var_dic

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