UnboundLocalError: cannot access local variable 'x' where it is not associated with a value

UnboundLocalError: cannot access local variable 'count' where it is not associated with a value means a function reads a local variable before it has been assigned. The usual trigger: the function assigns to a name that also exists as a global (count += 1). Any assignment makes the name local for the whole function body, so the global is no longer visible. Add global count, or better, pass the value in and return the result.

Reproduce it

cat > app.py <<'EOF'
count = 0

def increment():
    count += 1
    return count

increment()
EOF
python app.py

Traceback (most recent call last):
  File "/tmp/work/app.py", line 7, in <module>
    increment()
    ~~~~~~~~~^^
  File "/tmp/work/app.py", line 4, in increment
    count += 1
    ^^^^^
UnboundLocalError: cannot access local variable 'count' where it is not associated with a value

Python 3.10 and earlier report the same error as local variable 'count' referenced before assignment. Python 3.11 and later use the wording above.

Fixes

python - <<'EOF'
count = 0

def increment_global():
    global count            # change the module-level variable
    count += 1
    return count

def increment(value):       # preferred: no shared state
    return value + 1

def make_counter():
    total = 0
    def step():
        nonlocal total      # change the enclosing function's variable
        total += 1
        return total
    return step

print(increment_global(), increment(10))
step = make_counter()
print(step(), step())
EOF

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The other common form is a conditional assignment: a variable assigned only inside if found: and read after the if. Give it a default value before the branch.