# UnboundLocalError Local Variable 'index' Referenced Before Assignment

**URL:** https://sentry.io/answers/unbound-local-error/

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## The Problem

The exception `UnboundLocalError: local variable 'index' referenced before assignment` happens in Python when you use a global variable in a function that also defines a local version of the same variable.

```python
index = 0

def foo():
    if index == 0:
        print("ZERO")

    index = 1

foo()
```

Because index is defined globally as well as inside the `foo()` function, Python throws an exception if you try to use the variable inside `foo` before it's declared.

## The Solution

In this case, we want to rename the variable to avoid the conflict.

```python
index = 0

def foo():
    if index == 0:
        print("ZERO")

    findex = 1

foo()
```

### Further Reading

If you're looking to get a deeper understanding of how Python application monitoring works, take a look at the following articles:

- [Debugging Python errors](https://blog.sentry.io/debugging-python-errors/)
- [How Grofers meets unprecedented delivery demand](https://sentry.io/customers/grofers/)
- [Getting started with a Python SDK (docs)](https://docs.sentry.io/platforms/python/)

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*Source: [sentry.io/answers/unbound-local-error/](https://sentry.io/answers/unbound-local-error/)*