On Friday, December 2, 2011 5:53:47 PM UTC+8, Hrvoje Niksic wrote:
> Chris Angelico <ros...@gmail.com> writes:
>
> >> The hash can grow with (k,v) pairs accumulated in the run time.
> >> An auto memory management mechanism is required for a hash of a non-fixed
> >> size of (k,v) pairs.
> >
> > That's a hash table
>
> In many contexts "hash table" is shortened to "hash" when there is no
> ambiguity. This is especially popular among Perl programmers where the
> equivalent of dict is called a hash.
>
> > Although strictly speaking, isn't that "Python dicts are implemented
> > as hash tables in CPython"? Or is the hashtable implementation
> > mandated?
>
> It's pretty much mandated because of the __hash__ protocol.
I agree with you. When a hash is inserted with (k,v1) and then (k,v2)
such that v1!=v2, there are several possibilities to handle this situation
in programming:
1. v2 just replaces v1 with or without a message
2. the programmer can delete the (k,v1) entry and then insert a (k, (v1,v2))
entry.
3. the programmer initializes a tuple of (v1,v2), and then delete the (k,v1)
entry to be replaced by a (k,(v1,v2)) entry.
Hashes of hashes are really powerful in Python to be used to build a relational
DB of thousands of thousands of objects or records in a piece of cake.
A similar hash library in C is to be used everywhere is not difficult at all.
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