[Tutor] Word Jumble - Chpt4 (Explanation)

[Marc Tompkins]

On Thu, May 16, 2013 at 1:03 PM, Arvind Virk <arvind.s.virk at hotmail.co.uk>wrote:

 import random
>
> WORDS = ('python','jumble','easy','difficult','lower','high')
> word = random.choice(WORDS)
> correct = word
> jumble = ""
>
> while word:
>     position = random.randrange(len(word))
>     jumble += word[position]
>     word = word[:position] + word[(position+1):]
>
> ======
>
> I cannot understand what it is trying to do in the while loop.
> If the word was python and position lets say was 3 then jumble would =
> python(3). I cannot understand what the next line does! Please help!
>
> First, about "while word" - A 'while' loop runs as long as its condition
evaluates to True; an explanation of what evaluates to True can be found
here: http://docs.python.org/2/library/stdtypes.html, but for our purposes
it boils down to "as long as 'word' is not an empty string, keep going".

Second, what it's doing inside that while loop - it's picking a random
letter out of 'word', adding it to the end of 'jumble', and then removing
it from 'word'.  It's doing it by means of slices:  it takes all of 'word'
up to (but not including) 'position', then adds all of 'word' starting one
character AFTER 'position'.  'word' is now one character shorter than it
started out; keep this up long enough and you'll be left with an empty
string, which evaluates to False - and the 'while' loop terminates.

This is definitely not the most efficient way to do things, but it's a
pretty good introduction to slices (which are awesome, by the way.)
There's a very good introduction to Python's slice notation about halfway
down this page: http://docs.python.org/2/tutorial/introduction.html, in
section 3.1.2 "Strings".  Just remember that lists and indices start with
0, not 1, and you'll be on your way.

Finally, as Ramit mentioned, print statements (or print() functions, if
you're on Python 3) are your friend!  Don't be afraid or ashamed to put in
lots of them whenever you're not sure what your code is doing!  (Just
remember to take out the unnecessary one when you're done.)
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