Simple Encryption and Decryption Using a dictionary and keys

SimpleEncryption.py

chars = {
'!':-15,
'"':-14,
'=':-13,
'+':-12,
'-':-11,
'*':-10,
'#':-9,
'$':-8,
'%':-7,
'5':-6,
'4':-5,
'3':-4,
'2':-3,
'1':-2,
'0':-1,
'@':0,
'a':1,
'b':2,
'c':3,
'd':4,
'e':5,
'f':6,
'g':7,
'h':8,
'i':9,
'j':10,
'k':11,
'l':12,
'm':13,
'n':14,
'o':15,
'p':16,
'q':17,
'r':18,
's':19,
't':20,
'u':21,
'v':22,
'w':23,
'x':24,
'y':25,
'z':26,
'6':27,
'7':28,
'8':29,
'9':30,
' ':31,
'^':32,
'~':33,
'(':34,
')':35,
'?':36,
"\\":37,
'&':38,
'.':39
}
inv = {}
for key, val in chars.items():
    inv[val] = inv.get(val, []) + [key]
option = input('(E)ncrypt / (D)ecrypt?: ').lower()
word = input('Text: ').lower()
kay = input('Key: ')
kay = int(kay) / int(len(kay))
kay = str(kay)
kay = int(kay[0])
def encrypt(word):
    global kay
    global chars
    global inv
    myencstring =''
    for char in word:
        ore = chars[char]
        ore -= kay
        cher = str(inv[ore]).replace('[\'','')
        cher = cher.replace('\']','')
        myencstring += cher
    return myencstring
def decrypt(word):
    global kay
    global chars
    global inv
    mydecryptedstring =''
    for char in word:
        ore = chars[char]
        ore += kay
        cher = str(inv[ore]).replace('[\'','')
        cher = cher.replace('\']','')
        mydecryptedstring += cher
    return mydecryptedstring



if 'e' in option:
    print('Your Encrypted String: \033[31m'+encrypt(word)+'\033[0m')
elif 'd' in option:
    print('Your Decrypted String: \033[32m'+decrypt(word)+'\033[0m')

NOTE: This only "encrypts" characters and numbers, it will output a error if there is a symbol in the text you're trying to encrypt