morse code assignment

[raymond2688]

Going back over the assignment I really messed it up. It got the desired result but my code was not per instructions below is what i think step 1 should be but im getting an error.

def code(letter):
    if letter == A:
        code = ".-"
    elif letter == B:
        code = "-..."
    elif letter == C:
        code = "-.-."
    elif letter == D:
        code = "-.."
    return code

letter =(input("Please enter upper case letter to convert to morse code: "))
code = code(letter)
print("Your code for {} is {}.".format(letter,code))

This is the error:
Please enter upper case letter to convert to morse code: A
Traceback (most recent call last):
File "C:/Users/raymond/Documents/School/Python/week 3/step_1.py", line 17, in <module>
code = code(letter)
File "C:/Users/raymond/Documents/School/Python/week 3/step_1.py", line 6, in code
if letter == A:
NameError: name 'A' is not defined