# string_IsAlpha
Returns true if the given `string` is only the letters a-Z.

## Arguments
- str (string): the string to check.

## Returns
isAlpha (bool): returns `true` if `string` is only the letters a-Z, otherwise `false`.

## Example
### Ground
```python
call !string_IsAlpha "abcABC" &isAlpha
println $isAlpha # true

call !string_IsAlpha "123" &isAlpha
println $isAlpha # false

call !string_IsAlpha "abc_$@" &isAlpha
println $isAlpha # false

call !string_IsAlpha "aAbBcCdDeEfF" &isAlpha
println $isAlpha # true
```