How to use a variable in a function that is created via the exec()?

Question

I am trying to run the following code

def foo():
    exec('foo_value = 1')
    
def foo2():
    foo()
    print(globals()['foo_value'])

foo2()

But i get the error KeyError: 'foo_value'

Is there a way to be able to use the foo_value inside the foo2 function, while the foo_value is created inside another function via the exec() ?

this is highly suspect – juanpa.arrivillaga Jul 20 '20 at 11:58 — juanpa.arrivillaga, Jul 20 '20 at 11:58

Kasper · Accepted Answer · 2020-07-20T13:17:43.407

2

You can make foo_value a global variable by doing this: exec('global foo_value;foo_value = 1')

edited Jul 20 '20 at 13:17

answered Jul 20 '20 at 11:58

Kasper

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b9s · Answer 2 · 2020-07-20T12:12:35.873

2

If you want to set a global from inside a function, you need the global keyword. (see here)

def foo():
    global foo_val
    foo_val = 1

That should make it work. (Or exec('global foo_val;foo_val=1') inside an exec call)

edited Jul 20 '20 at 12:12

answered Jul 20 '20 at 11:58

b9s

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4
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score 2 · Answer 3 · answered Jul 20 '20 at 11:59

2

Yes. When you run the exec function, the code runs in a local scope. In order to make the code accessible to globals simply you can set your global scope in exec code like:

def foo():
    exec('foo_value = 1', globals())
    
def foo2():
    foo()
    print(globals()['foo_value'])

foo2() #output: 1

answered Jul 20 '20 at 11:59

PaxPrz

1,778
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Was not aware of the extra parameters of `exec`, good to know! I think I like that more. – b9s Jul 20 '20 at 12:01

score 1 · Answer 4 · answered Jul 20 '20 at 12:13

There is also a function called eval(), it is very similar to exec(), but you could get the returned value of eval()

def foo():
    global foo_val
    fool_val = eval("1")

Although both of them could convert string to code, I strongly don't recommend you using them, because they are unsafe.

How to use a variable in a function that is created via the exec()?

4 Answers4