[Tutor] Backwards message program

[Joel Goldstick]

On Tue, Feb 7, 2012 at 5:41 AM, Steven D'Aprano <steve at pearwood.info> wrote:
> myles broomes wrote:
>>
>> Im trying to code a program where the user enters a message and it is
>> returned backwards. Here is my code so far:
>>  message = input("Enter your message: ")
>>  backw = ""
>> counter = len(message)
>> while message != 0:
>>    backw += message[counter-1]
>>    counter -= 1
>> print(backw)
>> input("\nPress enter to exit...")
>
>
> When you want to do something with each item in a sequence, such as each
> character in a string, you can do it directly:
>
> for char in message:
>    print(char)
>
>
> prints the characters one at a time.
>
> Python has a built-in command to reverse strings. Actually, two ways: the
> hard way, and the easy way. The hard way is to pull the string apart into
> characters, reverse them, then assemble them back again into a string:
>
>
> chars = reversed(message)  # Gives the characters of message in reverse
> order.
> new_message = ''.join(chars)
>
>
> Or written in one line:
>
>
> new_message = ''.join(reversed(message))
>
>
> Not very hard at all, is it? And that's the hard way! Here's the easy way:
> using string slicing.
>
> new_message = message[::-1]
>
>
> I know that's not exactly readable, but slicing is a very powerful tool in
> Python and once you learn it, you'll never go back. Slices take one, two or
> three integer arguments. Experiment with these and see if you can understand
> what slicing does and what the three numbers represent:
>
>
> message = "NOBODY expects the Spanish Inquisition!"
>
> message[0]
> message[1]
>
> message[39]
> message[38]
>
> message[-1]
> message[-2]
>
> message[0:6]
> message[:6]
>
> message[19:38]
> message[19:-1]
> message [19:-2]
>
> message[::3]
> message[:30:3]
> message[5:30:3]
>
>
> Hint: the two and three argument form of slices is similar to the two and
> three argument form of the range() function.
>
>
> Python gives you many rich and powerful tools, there's no need to mess about
> with while loops and indexes into a string and nonsense like that if you
> don't need to. As the old saying goes, why bark yourself if you have a dog?
>
>
>
> --
> Steven
>
>
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While you should know about reverse, and understand slices, your
program will work if you test for while counter != 0 instead of
message.  Message doesn't change

message = input("Enter your message: ")

backw = ""
counter = len(message)

#while message != 0:         # not this
while counter != 0:             # this
    backw += message[counter-1]
    counter -= 1

print(backw)
input("\nPress enter to exit...")


-- 
Joel Goldstick