[Tutor] Remove a dictionary entry

[Alan Gauld]

"Alan Gauld" <alan.gauld at btinternet.com> wrote

>> I ended up with this :
>>
>> Version 3 :
>> for i,row in d[:].iteritems() : # BUG : TypeError: unhashable type
>>    if len(row) < 2 :
>>        del d[i]
>
> You are getting too complicated.
> You don't need the slice and you don't need iteritems.
> You have a dictionary. When you iterate over a dictionary
> what do you get? Don't know? Try it::
>
>>>> for x in {1:'foo',2:'bar'}: print x
> ...
> 1
> 2
>
> So we get the keys. Now how do we use the keys to get the list?
> Standard dictionary access:
>
>>>> print d[1]
> foo
>
> You know how to test the lenth of the list and delete the list so 
> put
> that together as you did before:
>
> for row in d :     # row is actually the key
>   if len(row) == 1 :        # so use the key to get the real row
>     del row # WRONG      #' and delete the row, again using the key
>

Oops, as Peter pointed out that won't work because its changing
the iterable while we iterate. (I actually thought it would be OK
because the for would use a copy of the keys() list, but I was 
wrong...)
But you can fix that with a list() call:

for row in list(d) :     # generates a new list of the dict keys
   if len(d[row]) == 1 :        # so use the key to get the real row
     del d[row]


HTH,


-- 
Alan Gauld
Author of the Learn to Program web site
http://www.alan-g.me.uk/




> HTH,
>
>
> -- 
> Alan Gauld
> Author of the Learn to Program web site
> http://www.alan-g.me.uk/
>
>
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