order independent hash?

[88888 Dihedral]

On Friday, December 2, 2011 1:00:10 PM UTC+8, Chris Angelico wrote:
> On Fri, Dec 2, 2011 at 3:29 PM, 88888 Dihedral
> <dihedr... at googlemail.com> wrote:
> > I clear my point a hash is a collection of (key, value) pairs that have
> > well defined methods and behavior to be used in programming.
> >
> > The basic operations of a hash normally includes the following:
> >
> > 1. insertion of a (key, value) pair  into the hash
> > 2. deletion of a (key, value) from the hash
> > 3. inquiring  a hash by a key to retrieve the value if the (key, value)
> > pair available in the hash. If no key matched, the hash will return
> > a not found result.
> >
> > 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 - think of a Python dictionary:
> 
> On Fri, Dec 2, 2011 at 3:33 PM, Steven D'Aprano
> <steve+comp.... at pearwood.info> wrote:
> > Python dicts are hash tables.
> 
> Although strictly speaking, isn't that "Python dicts are implemented
> as hash tables in CPython"? Or is the hashtable implementation
> mandated? Anyway, near enough.
>

 
> Cryptography and data verification use hashing too (look at the
> various historic hashing algorithms - CRC, MD5, SHA, etc). The concept
> of a hash is a number (usually of a fixed size) that is calculated
> from a string or other large data type, such that hashing the same
> input will always give the same output, but hashing different input
> will usually give different output. It's then possible to identify a
> large object solely by its hash, as is done in git, for instance; or
> to transmit both the data and the hash, as is done in message
> protection schemes (many archiving programs/formats include a hash of
> the uncompressed data). These have nothing to do with (key,value)
> pairs, but are important uses of hashes.
> 
> ChrisA

If one tries to insert a (k,v1) and then a (k,v2) pair into a
hash with v1 not equals V2, what could happen in your understanding of
a hash?

A hash function is different from a hash or so called a hash table in
my post. 
 
If the hash collision rate is not specified, then  it is  trivial to write a hash function with the conditions you specified. A hash function applied to a set of data items only  is of very limited use at all.
 
A hash stores (k,v) pairs specified in the run time with auto memory
management build in is not a simple hash function to produce data signatures only clearly in my post.   

What I said a hash which is lifted as a basic type in python  is called a dictionary in python. 

It is called a map in c++'s generics library.