如何摆脱最后的空白？

Question

i'm just a beginner to python and i have been asked to solve a problem where your program has to decode a code in which it takes every 3rd letter and puts them together with a gap in between each letter, sorry that was a bad explanation but have a look at my code:

    m=input("Message? ")
    for c in m[::3]:
      print(c,end=' ')

the problem is there's a whitespace after the last letter and i dont know how to get rid of it, i've tried.rstrip and that doesnt work. i've also tried to [::-1]after the end=' ' and that doesn't work.

Answer 1

You could use str.join on a list comprehension rather than a loop:

" ".join(m[::3])

This would put a space between each letter, excluding the trails.

Answer 2

I'm not sure what the problem is exactly but I'm assuming you mean to say that on your last print you do not want the end=' ' whitespace. To produce the string you want you can join the slice on whitespace as lltt said, minus the redundant list comprehension.

m = "123456789"
print(" ".join(m[::3]))

Output:

"1 4 7"

If you really want to maintain your for loop print functionality you need a way to determine if you are in the last loop. This is a general problem which has various solutions such as a look-ahead function. But you can simply break up the for loop into two parts.

m="123456789"
for c in m[::3][:-1]:
    print(c,end=' ')
print(m[::3][-1], end='')

Output:

1 4 7

Of course you do not need the end='' in the last print; print(m[::3][-1]) is fine. It is just there for readability.

If you mean to say that the decoded message cannot have a whitespace as the last character then you can use.rstrip(). For example when the last, third character of the input, is a whitespace.

m = "input with trailing whitespace "
print(" ".join(m[::3]))

Output:

"i u w h r l g h e a  "

Here you can chain the rstrip() method.

m = "input with trailing whitespace "
print(" ".join(m[::3]).rstrip())

Output:

"i u w h r l g h e a"

Answer 3

When working with strings, you should avoid hand-crafted solutions that are inefficient and often incorrect. Connect the letters with spaces using the string method .join() :

m = "Hello, world!"
print(" ".join(m[::3]))
#'H l w l'