[Tutor] Question

[Felix Dietrich]

Lucia Stockdale <Lucia.Stockdale at mggs.vic.edu.au> writes:

> I have been writing a program to print words backwards until an an
> empty line of input is entered, but after I put in the input it comes
> up with TypeError.

For completeness give us the whole Traceback, it makes pin-pointing the
error easier.  Also, tell us which Version of /python/ you are using.  I
assume you are using python3, because you did not get a SyntaxError in
/input/ (in python2 /input/ evaluates the string as python-code).

> This is my current code:
>
> line = input('Line: ')
> while line != '':
>   line = line[len(line):0:-1]
>   line = line.split()
>   line = line.reverse()

Reverse mutates the list /line/ and returns None, which you then assign
to /line/.  Returning None is a common pattern for python methods mutating
the objects value and not creating a copy.

>   line = (' '.join(line))

Your calling of

    ' '.join(None)

results in a TypeError here.  str.join takes an iterable.

>   print(line)

After the call to /print/ you probably want to duplicate the line

    line = input('Line: ')

or you will end up in an infinite loop, since your program does not read
another line of input and therefore the value of /line/ never changes
and gets no chance to become the empty string.

-- 
Felix Dietrich