How can I assign the value of a variable using eval in python?

Question

Okay. So my question is simple: How can I assign the value of a variable using eval in Python? I tried eval('x = 1') but that won’t work. It returns a SyntaxError. Why won’t this work?

Asked By: tew

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Source

Answer 1

You can’t, since variable assignment is a statement, not an expression, and eval can only eval expressions. Use exec instead.

Better yet, don’t use either and tell us what you’re really trying to do so that we can come up with a safe and sane solution.

Answered By: Rafe Kettler

Answer 2

Because x=1 is a statement, not an expression. Use exec to run statements.

>>> exec('x=1')
>>> x
1

By the way, there are many ways to avoid using exec/eval if all you need is a dynamic name to assign, e.g. you could use a dictionary, the setattr function, ~~or the locals() dictionary~~:

>>> locals()['y'] = 1
>>> y
1

Update: Although the code above works in the REPL, it won’t work inside a function. See Modifying locals in Python for some alternatives if exec is out of question.

Answered By: kennytm

Answer 3

x = 0
def assignNewValueToX(v):
    global x
    x = v

eval('assignNewValueToX(1)')
print(x)

It works… cause python will actually run assignNewValueToX to be able to evaluate the expression. It can be developed further, but I am sure there is a better option for almost any needs one may have.

Answered By: sanyi

Answer 4

You can actually put exec() command inside eval()

So your statement would look like eval("exec('x = 1')")

p.s. this is dangerous

Answered By: Domchix

Answer 5

you can use lambda, like this:

eval('(lambda x=10: x+2)()')

Answered By: Ganes Dipa

How can I assign the value of a variable using eval in python?

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