> OK, all of this is perfectly clear but what is still difficult for me
> to understand is the following. If you remember the line of code in
> question was:
>
> >sorted(word_table.items(), key=lambda item: item[1], reverse=True)
>
> This is supposed to return a list of tuples such as
>
> [('the', 3), ('in', 1), ('fig', 1)]
>
> If this list of tuples is what is in the context, why is item[1]
> referring to the second position in any tuple and not to the second
> tuple in the list of tuples? I mean, if I do:
Because sorted() passes each item in the sequence being
sorted to the function defined in key, like this:
def sorted(seq, key):
result = []
for item in seq:
sortVal = key(item)
insertItemInResult(item,sortVal,result)
return result
Notice that it uses key as a function inside sorted.
And lambda creates a function so sorted applies
the lambda to each item in turn to retrieve the sort key.
> I guess I'm having trouble figuring out what the scope of the variable
> 'item' is in this case. Why is tuple[1] in this line of code
> interpreted to mean "the second position in any of the tuples" and not
> "the second tuple in the available list of tuples".
Because item in the lambda is a local variable within the lambda.
When the lambda is used inside sorted the value of item is
a single tuple of your sequence.
> Perhaps this is a very stupid question but it is hard for me
> to wrap my mind around this.
It is a biot odd when you aren't used to thinking of function 'objects'
that can be passed around like data and then executed. But it is
a very powerful technique once you get your head wrapped around it.
[ FWIW Languages like C do the same thing with the concept of a
pointer to a function. ]
HTH,
Alan G.
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