Implement a function called makeAcronym that returns the first letters of each word in a passed in string.
Make sure the letters returned are uppercase.
If the value passed in is not a string return 'Not a string'.
If the value passed in is a string which contains characters other than spaces and alphabet letters, return 'Not letters'.
If the string is empty, just return the string itself: "".
**EXAMPLES:**
```
'Hello codewarrior' -> 'HC'
'a42' -> 'Not letters'
42 -> 'Not a string'
[2,12] -> 'Not a string'
{name: 'Abraham'} -> 'Not a string'
```
def make_acronym(phrase):
    if not isinstance(phrase, str): return 'Not a string'
    arr = phrase.split()
    return ''.join(a[0] for a in arr).upper() if all(map(str.isalpha, arr)) else 'Not letters'       
def make_acronym(phrase):
    if not isinstance(phrase, str): return 'Not a string'
    arr = phrase.split()
    return ''.join(a[0] for a in arr).upper() if all(map(str.isalpha, arr)) else 'Not letters'       