How to get the value of a variable given its name in a string?

Question

For simplicity this is a stripped down version of what I want to do:

def foo(a):
    # I want to print the value of the variable
    # the name of which is contained in a

I know how to do this in PHP:

function foo($a) {
    echo $$a;
}

global $string = "blah"; // might not need to be global but that's irrelevant
foo("string"); // prints "blah"

Any way to do this?

Asked By: dsavi

||

Source

Answer 1

>>> x=5
>>> print eval('x')
5

tada!

Answered By: maxm

Answer 2

Assuming that you know the string is safe to evaluate, then eval will give the value of the variable in the current context.

>>> string = "blah"
>>> string
'blah'
>>> x = "string"
>>> eval(x)
'blah'

Answered By: stark

Answer 3

If it’s a global variable, then you can do:

>>> a = 5
>>> globals()['a']
5

A note about the various “eval” solutions: you should be careful with eval, especially if the string you’re evaluating comes from a potentially untrusted source — otherwise, you might end up deleting the entire contents of your disk or something like that if you’re given a malicious string.

(If it’s not global, then you’ll need access to whatever namespace it’s defined in. If you don’t have that, there’s no way you’ll be able to access it.)

Answered By: Edward Loper

Answer 4

Edward Loper’s answer only works if the variable is in the current module. To get a value in another module, you can use getattr:

import other
print getattr(other, "name_of_variable")

https://docs.python.org/3/library/functions.html#getattr

Answered By: eresonance

How to get the value of a variable given its name in a string?

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