On Fri, Dec 2, 2011 at 3:29 PM, 88888 Dihedral <dihedral88...@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.lang.pyt...@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 -- http://mail.python.org/mailman/listinfo/python-list
