How to execute a string as a variable within a function or a for loop?

Question

Lets say I have the following function

def code_string(a):
    for i in range(a):
        exec('f=a+i')
        print(f)

When I run it in the using the following command

code_string(3)

It gives me the following error

---------------------------------------------------------------------------
NameError                                 Traceback (most recent call last)
<ipython-input-4-9c91de8067f3> in <module>()
----> 1 code_string(3)

<ipython-input-2-2ae9915b0a25> in code_string(a)
      2     for i in range(a):
      3         exec('f=a+i')
----> 4         print(f)

NameError: name 'f' is not defined

when I run it not in the function as so

a=3
for i in range(a):
    exec('f=a+i')
    print(f)

It works perfectly fine as so

3
4
5

Why is this happening and can I execute a string code within a function in python

NOTE: This is only a demo example, please do not expect my code to be as simple as this demo example. I just put it to demonstrate the problem.

Dino · Accepted Answer · 2019-11-09 15:58:38Z

1

You can try this:

def code_string(a):
    for i in range(a):
        exec('f=a+i', locals(), globals())
        print(f)

edited Nov 9, 2019 at 15:58

Dino

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answered Nov 9, 2019 at 14:24

nonamer92

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1 Comment

rsc05 Over a year ago

Thank you for this, it worked but why it is important to mention locals and globals?

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