Sample Encryption Program for Beginners

# Sample Encryption Program for beginners
# This program only handles lowercase alphabetical letters.
import time

def encrypt(phrase):
    ''' (string) -> string
    Return an encrypted version of the inputted phrase
    through scrambling along with other substitutions.
    >>> encrypt("fries")
    "51FRe"
    >>> encrypt("personality")
    "Y7a0RPe5N1T"
    '''
    encryption_dict = {'l':1,'z':2,'s':5,'b':6,'i':7,'g':9,'o':0, ' ':8}
    encrypted = ''
    scrambled = scramble(phrase)

    for i in scrambled:
        if i in encryption_dict:
            encrypted += str(encryption_dict.get(i))
        elif i in 'aeiou':
            encrypted += i
        else:
            encrypted += i.upper()

    return encrypted


def scramble(phrase):
    ''' (string) -> string
    Return a scrambled version of the inputted phrase
    through multiple reverses.
    >>> scramble("fries")
    "sifre"
    >>> scramble("personality")
    "yiaorpesnlt"
    '''
    scrambled = ''
    phrase_half = len(phrase) // 2
    scrambled = reverse(phrase[0::2]) + phrase[1::2]
    return scrambled

def reverse(phrase):
    ''' (string) -> string
    Return a reversed version of the inputted phrase.
    >>> reverse("kill")
    "llik"
    >>> reverse("drag")
    "gard"
    '''
    reversal = ''
    for i in phrase:
        reversal = i + reversal
    return reversal

def check(phrase):
    ''' (string) -> bool
    Return True if the inputted string contains only
    alphabetical characters or whitespace and false otherwise.
    '''
    for i in phrase:
        if not(i.isalpha() or i == " "):
            return False
    return True

# Main function
print("Welcome to my encryption program!")
print("This program only handles lowercase alphabetical letters.")
time.sleep(0.5)
more = True
while more:
    clause = input("\nPlease enter a phrase: ")

    while not check(clause):
        print("An invalid phrase has been entered.")
        clause = input("\nPlease enter a valid phrase: ")

    if not clause.islower():
        print("Converting phrase to lowercase ...")
        time.sleep(1)

    print("Encrypting your message ...")
    time.sleep(2)
    print(reverse(clause.lower()))
    print(scramble(clause.lower()))
    print(encrypt(clause.lower()))
    answer = input("\nWould you like to encrypt another phrase? (Y/N)")
    while not(answer.lower() == 'n' or answer.lower() == 'y'):
        print("Invalid input.")
        answer = input("\nWould you like to encrypt another phrase? (Y/N)")
    if answer.lower() == 'n':
        more = False
    elif answer.lower() == 'y':
        more = True
    time.sleep(1)

print("All done!")