SO: how-to-fix-infinite-printing-on-while-statement

# https://stackoverflow.com/questions/57651384/how-to-fix-infinite-printing-on-while-statement

# As I said in comment you forgot `x = x + 1` when you display `" "` so it never move to next char in message
# and it check again and again the same char which is converted to `" "`

    import string

    letras = list(string.ascii_lowercase)
    message = input("qual sua menssagem codificada?")
    cod = input("qual a numeração da cifra?")
    meslist = list(message)

    trans = True
    num = len(meslist)
    x = 0
    while trans:

        if num > x:
            if meslist[x] in letras:
                a = letras.index(meslist[x])
                print(letras[a + 2])
                x = x + 1
                trans = True
            else:
                print(" ")
                x = x + 1   # <---
                trans = True
        elif num == 0:
                trans = False

# But you could write it with `for` loop and then you don't need `x` and `trans`

# You also forget that sometimes `letras[a + 2]` may give error `IndexError: list index out of range`
# and then in `caesar cipher` you have to move to beginning `letras[ a+2-len(letras) ]`
# (or alwasy take modulo `letras[ a+2 % len(letras) ]`)

    import string

    letters = string.ascii_lowercase

    message = input("message: ")
    code = int(input("number: "))

    for char in message:
        if char in letters:
            position = letters.index(char)
            position += code # position += 2
            if position > len(letters):
                position -= len(letters)
            print(letters[position], end='') # don't go to new line
        else:
            print(" ", end='') # don't go to new line

    print()  # go to new line