[Python] how to generate correct output using 2 yield statements in coroutine?

i have var DICTIONARY, which is a dictionary where the keys are English letters and the values are words that start with the corresponding letter. The initial filling of DICTIONARY looks like this:

DICTIONARY = {
'a': 'apple',
'b': 'banana',
'c': 'cat',
'd': 'dog',
...
}


i'm trying to write coroutine called alphabet, which takes letters as input and returns the words associated with the given letter from the DICTIONARY.

Sample Input 1:

coro = alphabet()
next(coro)
print(coro.send('a'))
print(coro.send('b'))
print(coro.send('c'))

Sample Output 1:
text
apple
banana
cat

Sample Input 2:
python
coro = alphabet()
next(coro)
for letter in 'qwerty':
print(coro.send(letter))

Sample Output 2:
text
quail
walrus
elephant
rabbit
tiger
yak


my code uses 2 yields , 1 is assigned as variable:

def alphabet():
while True:
ch = yield
yield DICTIONARY[ch]


however 2 yield statements used in coroutine actually skip 1 value always:

Test input:
coro = alphabet()
next(coro)
print(coro.send('a'))
print(coro.send('b'))
print(coro.send('c'))
Correct output:
apple
banana
cat

Your code output:
apple
None #this is the problem
cat


i dont know how to deal with None and it skips 'b' for banana.

updated:

#still dont really get it how it works
def alphabet(letter='a'):
while True:

letter = yield DICTIONARY[letter]

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