[Tutor] Eek, help!

[Liam Clarke]

Hi all,

Kent - Sorry, misworded that one. pause.anyKey() is a little function
I wrote because I missed INKEY$(1) from the days of QBASIC. It works
fine.

Danny - Thanks a bundle, it works great now!

Regards,

Liam Clarke

On Thu, 4 Nov 2004 11:24:06 -0800 (PST), Danny Yoo
<dyoo at hkn.eecs.berkeley.edu> wrote:
> 
> > I have belatedly come to use dictionaries, and I was having some
> > trouble with how to read/write them from a file,  so I looked at Alan
> > Gauld's section on it. I've pretty much copied his code straight
> > through, and, well, I've broken it somehow. In fact, it's hanging
> > Python, and it even hangs the debugger, which is a first, I must
> > admit.
> 
> Hi Liam,
> 
> Whenever I hear something about a "hang", I almost immediately look at
> while loop conditions.  *grin* Let's take a look:
> 
> 
> > store2 = file(filename,'r')
> >
> > while store2:
> >     name = store2.readline().strip()
> >     entry = store2.readline().strip()
> >     book[name] = entry
> 
> 
> The while loop here needs to be fixed: store2 is a file, and files are
> true values, no matter what.  This is an infinite loop.
> 
> What you wanted to say, I think, was to keep the loop running as long as
> there's still content in store2.  When we read the end of a file, we'll
> get the empty string from a readline.  So one way to correct the loop may
> be:
> 
> ###
> while True:
>     name, entry = store2.readline(), store2.readline()
>     if not name or not entry: break
>     name, entry = name.strip(), entry.strip()
>     book[name] = entry
> ###
> 
> This is a little more verbose, and might look weird at first, with the
> 'while True' thing.
> 
> The input is not exactly single-line oriented --- you're reading pairs of
> lines at a time --- so it complicates matters slightly.
> 
> Hmmm... We can make the code a little nicer by pairing up adjacent lines.
> Here's a small utility function that may help:
> 
> ###
> def groupAdjacentElements(someSequence, n = 2):
>     """A little helper utility to group up adjacent elements."""
>     nextGroup = []
>     for element in someSequence:
>         nextGroup.append(element)
>         if len(nextGroup) == n:
>             yield tuple(nextGroup)
>             nextGroup = []
> ###
> 
> This bit of code will pair up adjacent elements, like this:
> 
> ###
> >>> for a, b in groupAdjacentElements(range(20)):
> ...     print a, b,  a * b
> ...
> 0 1 0
> 2 3 6
> 4 5 20
> 6 7 42
> 8 9 72
> 10 11 110
> 12 13 156
> 14 15 210
> 16 17 272
> 18 19 342
> ###
> 
> With this helper, now the code that reads store2 can be written as a nice
> 'for' loop instead of the 'while' loop:
> 
> ###
> store2 = file(filename,'r')
> 
> for (name, entry) in groupAdjacentElements(store2):
>     name = name.strip()
>     entry = entry.strip()
>     book[name] = entry
> 
> store2.close()
> ###
> 
> I hope this helps!
> 
> 


-- 
'There is only one basic human right, and that is to do as you damn well please.
And with it comes the only basic human duty, to take the consequences.