Check if variables exist in locals()

Question

I am encountering a weird situation. I want to check if my variables x, y, z exist.

To do that, I tried:

>>> [var in locals() for var in ["x", "y", "z"]]
[False, False, False]

Then, I assign x, y, z to some values:

>>> x, y, z = 1, 2, 3

Nevertheless, I still have:

>>> [var in locals() for var in ["x", "y", "z"]]
[False, False, False]

But x, y, z exist one by one:

>>> for var in ["x", "y", "z"]: 
...     print(var in locals())
... 
True
True
True

Does someone have an explanation?

Also: [Can't use locals() in list comprehension in Python 3?](https://stackoverflow.com/q/55084171/7851470) — Georgy, Feb 27 '20 at 12:58

score 6 · Accepted Answer · answered Feb 27 '20 at 12:53

See:https://portingguide.readthedocs.io/en/latest/comprehensions.html

In Python 3, list expressions have their own scope: they are functions, just defined with a special syntax, and automatically called. Thus, the iteration variable(s) don’t “leak” out:

Reference locals() outside of the comprehension

>>> my_locals = locals()
>>> [var in my_locals for var in ["x", "y", "z"]]
[True,True,True]

Check if variables exist in locals()

1 Answers1