Python Function- Return Value is 'not defined' - function

Question

For my encryption code, I am trying to a return a value from one function because it is used in the next. I keep getting an error, telling me that the name 'cipher_text' is not defined. Please help!
Error:
(line 7)
decryption (cipher_text, shift)
NameError: name 'cipher_text' is not defined
def main():
user_input = input ("Enter string: ")
shift = int(input ("Enter a shift that is between 1 and 26: "))
while shift<1 or shift>26:
shift = input ("ERROR: Shift must be between 1 and 26: ")
encryption (user_input, shift)
decryption (cipher_text, shift)
frequency (user_input)
def frequency(user_input):
freq_char = None
for char in user_input:
charcount = user_input.count(char)
if (charcount != 0):
freq_char = char
print (freq_char)
return fre_char
def encryption(user_input, shift):
cipher_text = ''
for char in user_input: #for every character in input
if char == ' ':
cipher = char
cipher_text += cipher
else:
cipher_num = (ord(char))+(shift)%26 #using ordinal to find the number
cipher= ''
cipher = chr(cipher_num)# using chr to convert back to a letter
cipher_text += cipher
print ("The encrypted text is:",cipher_text)
return(cipher_text)
def decryption (cipher_text, shift):
decrypt_text = ''
cipher_text = ''
for char in cipher_text: #for every character in the encrpted text
decrypt_num = (ord(char))+(int(shift))%26
decrypt= ''
decrypt = chr(decrypt_num)
decrypt_text += decrypt
print("The decrypted text is:", decrypt_text)
return(decrypt_text)
main()

Answer 1

Your problem is in the lines
encryption (user_input, shift)
decryption (cipher_text, shift)
as the exception tells you. If you had included the traceback with your question this would be very clear.
Variables you declare in one function are local to that function. This is a good thing! It lets you write functions like
def foo():
x = 1
return x * x
def bar():
for x in xrange(10):
print "Count: %s" % x
without them blowing each other up.
If you call a function that returns something and you want to use it, you need to use it directly, or assign it to something:
# assign
x = foo()
print x
# use directly
print "x is %s" % foo()
in your case, you can make a minimal change to assign the result of encryption to a new variable cipher_text
def main():
...
cipher_text = encryption(user_input, shift)
decryption(cipher_text, shift)
it would be equivalent (though less clear) to call this anything else
foobar = encryption(user_input, shift)
decryption(foobar, shift)
or even to avoid use of a variable altogether
decryption(encryption(user_input, shift), shift)

Answer 2

def main() should be def main(cipher_text)
You can also set a default value for cipeher_text:
def main(cipher_text=""):
user_input = input ("Enter string: ")
shift = int(input ("Enter a shift that is between 1 and 26: "))
while shift<1 or shift>26:
shift = input ("ERROR: Shift must be between 1 and 26: ")
encryption (user_input, shift)
decryption (cipher_text, shift)
frequency (user_input)
And then just call main() using a value example main('some value') or just empty if you defined a default value as said before.