reverse_str

def reverse_str(source:str) -> str:
    if not source or not isinstance(source, str) or len(source) < 2:
        return "Bad input!!"
        
    reversed_arr = []
    for i in range(len(source)-1, -1, -1):
        reversed_arr.append(source[i])
    
    return ''.join(reversed_arr)

invalid_source = "M"
rev = reverse_str(invalid_source)
print("INVALID CASE - too short")
print(invalid_source)
print(rev)

invalid_source = None
rev = reverse_str(invalid_source)
print("\nINVALID CASE - None")
print(invalid_source)
print(rev)

invalid_source = ["invlid input"]
rev = reverse_str(invalid_source)
print("\nINVALID CASE - non-str")
print(invalid_source)
print(rev)

print("\nVALID CASE")
source = "My name is Atif."
rev = reverse_str(source)
print(source)
print(rev)