UnboundLocalError: cannot access local variable 'x' where it is not associated with a value
A function assigns to a variable somewhere, which makes it local everywhere in that function — so reading it before the assignment fails.
referenced before assignmentcannot access local variable Meaning
Python decides scope at compile time. If a function contains x = ..., every x in that function is local, even before the assignment. Modifying a module-level counter inside a function is the classic case.
Common causes
- Incrementing a global inside a function (count += 1)
- Variable assigned only in one branch
- Assigned in try but used in except/finally
⚡ Quick fix
- Pass values in and return results instead of using globals
- Use global/nonlocal deliberately
- Initialise before branches
Detailed fix by platform
Python
- python
def increment(): global counter counter += 1
How to diagnose
- Assignment — Where is it assigned in the function?
- Read — Is it read before that?
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Last updated 15 Oct 2026