The conversation between human and AI assistant.
[|Human|] Clean up the following piece of code.
[|AI|] Here's a cleaner version of the code:

```python
def count_vowels(string):
    vowels = ['a', 'e', 'i', 'o', 'u']  
    count = 0
    
    for char in string:
        if char.lower() in vowels:
            count += 1
    
    return count
```
[|Human|] 
Clean up the following piece of code.