Python - replace exec for dynamic variable creation

Question

I have been told that using exec is a Very Bad Thing.

However, I'm new to python and trying to figure out how to dynamically create a bunch of global variables (I'm aware that this is also supposed to be a Bad Thing, but let's burn one bridge at a time, shall we?).

What this is doing: get a list of the current variables that need to be created (currently sitting in a CSV), get the unique ID's within that list, then create the necessary objects by appending the ID to the name and reading the content of another CSV into it.

import pandas as pd

def importtest():
    ilist = pd.read_csv('Z:/fakepath/ID.csv')
    for i in range(0, len(ilist['ID'].unique())):
        tempID = ilist['ID'].unique()[i]
        exec("variable%s = pd.read_csv('%s')" % (
            str(tempID), 'Z:/fakepath/'+str(tempID)+'.csv'), globals())
        i = i + 1

Is there another/better way to dynamically create/update the variables I need so they show up in the global scope?

As you seem to be aware, this is not a good idea. Why do you want to do this? Just make a global dictionary called variable, and then do variable[tempID] = whatever. What problem do you have that that does not solve? — BrenBarn
– BrenBarn, Commented Nov 23, 2015 at 7:24
Looks like that solves both of my problems, actually. Thanks! — Lincoln Johnson
– Lincoln Johnson, Commented Nov 23, 2015 at 7:37
@BrenBarn, might as well write it up as an answer so the original poster can mark it correct. A couple minor comments -- I don't think you need the i = i + 1 line, since your i is looping already anyway. Also, I think it would be cleaner to write for temp_id in ilist['ID'].unique(): instead of creating an index. The id values are all you actually care about, so just loop over those. — dslack
– dslack, Commented Nov 23, 2015 at 8:54

merletta · Accepted Answer · 2015-11-23 08:19:56Z

4

String keys in globals() dictionary correspond to variable names, so, you don't need to use exec, you can write variable to globals hash directly:

     globals()["variable" + str(tempID)] = pd.read_csv('Z:/fakepath/'+str(tempID)+'.csv')

answered Nov 23, 2015 at 8:19

merletta

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1 Comment

Lincoln Johnson Over a year ago

Accepting this answer, because while BrenBarn's comment solved my problem, I feel that this answer is actually a closer solution to my question as asked.

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