### count_vowels

Retuns `number` of vowels in provided `string`.

Use a regular expression to count the number of vowels `(A, E, I, O, U)` in a string.

```python 


import re


def count_vowels(str):
    return len(len(re.findall(r'[aeiou]', str, re.IGNORECASE)))

```

``` python
count_vowels('foobar') # 3
count_vowels('gym') # 0
```