Monoalphabetic cipher

[pawlo392]

Hello!
I wrote this code:

keys={'a':'z','b':'y','c':'x','d':'w','e':'v','f':'u','g':'t','h':'s','i':'r','j':'q','k':'p','l':'o','m':'n'}
reverse_keys={}
for key,value in keys.items():
    reverse_keys[value]=key
def encrypt(text):
    text=str(text)
    encrypting=[]
    for l in text:
        encrypting.append(keys.get(l,l))
    print(''.join(encrypting))
def decipher(text):
    text=str(text)
    decrypted=[]
    for l in text:
        decrypted.append(reverse_keys.get(l,l))
    print(''.join(decrypted))
print(encrypt("hej"))
print(decipher("svq"))

But now I want to create a function encrypt(text,keys) for example encrypt(hej,"zyxwvutsrqponmlkjihgfedcba"). I want the user to define the key himself.