Use variable name, not its value [duplicate]

Question

What?

I want to use a variable's name, not it's value. For instance, in the following example, I would like the function to return my_list[1] , and not B..

my_list = ['A', 'B']
def example(list_element):
   print(repr(eval(list_element)))

example(my_list[1]) # I would like this to print `my_list[1]`

But Why?

I am trying to create a function that takes a given element from a list, and also uses the previous list element. By getting the name my_list[1], I can subtract one and also get my_list[0]. Once I have both the names, I can utilise the values stored under these names.

Yes, I could simply add two fields to the function and put them in each time but I was hoping to keep the body of my code a little easier to read.

Objects don't know which variables they happen to be bound to at any given time. Are you planning on hardcoding this to only work with one specific variable "my_list" or should be be generic? — tdelaney
– tdelaney, Commented Dec 16, 2020 at 20:30
@grismar What do you propose instead? leaving the same questions open? I put the "Dont do it" and advice of "return a slice from the list or maybe a tuple of prev/act value" in the comment. if we leave it open, the same bad crappy answers turn up - using eval, using inspect, search through global() etc — Patrick Artner
– Patrick Artner, Commented Dec 16, 2020 at 20:38
@PatrickArtner - no, providing a simple answer that goes into the difference between data and code. Mine below is about as simple an answer as OP needed. You could write a nicer answer that concisely explains the difference and results in a similar solution. What the referenced answers do is "sure, if you want to be an idiot: here's how" - they're not wrong, but they're no good to the beginning coders that just don't know any better and the answer will just send them further down a dead end. — Grismar
– Grismar, Commented Dec 16, 2020 at 20:41
@SolebaySharp - that's good to hear, and means you're on your way to better things. My comment was more general, questions like these come up more than daily. But thanks for the feedback. I think we can leave this as it is :) — Grismar
– Grismar, Commented Dec 16, 2020 at 20:44

Grismar · Accepted Answer · 2020-12-16 20:32:03Z

2

Don't use data to manipulate your code, it's not how Python (or most languages) works.

To do what you're trying to do:

my_list = ['A', 'B']


def example(a_list, index):
    print('The element passed: ', a_list[index])
    print('The element before it: ', a_list[index-1])


example(my_list, 1)

Of course this doesn't check if you didn't accidentally pass 0, etc. - but it shows you don't need to make a mess with eval, exec, etc.

answered Dec 16, 2020 at 20:32

Grismar

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1 Comment

Solebay Sharp Over a year ago

Thank you, this is a sensible solution.

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