Re: Tuples vs Lists: Semantic difference (was: Extract String From Enclosing Tuple)
George Sakkis, I agree with the things you say. Sometimes you may have a sequence of uniform data with unknown len (so its index doesn't have semantic meaning). You may want to use it as dict key, so you probably use a tuple meant as just an immutable list. I don't know Ruby, but I think it allows such purposes with a freezing function. Bye, bearophile -- http://mail.python.org/mailman/listinfo/python-list
Re: Tuples vs Lists: Semantic difference (was: Extract String From Enclosing Tuple)
On Mar 1, 5:02 am, [EMAIL PROTECTED] wrote: I don't know Ruby, but I think it allows such purposes with a freezing function. In ruby all objects can be frozen (freeze is a method on Object, from which all other objects derive), not just Arrays (Arrays == lists in python; ruby has no built-in container equiv. to tuple). But that's more of an implementation detail rather than anthing to do with the structure/semantics of a certain type of object (e.g., a String can be frozen, a Hash can be frozen, c). Regards, Jordan -- http://mail.python.org/mailman/listinfo/python-list
Tuples vs Lists: Semantic difference (was: Extract String From Enclosing Tuple)
Bjoern Schliessmann [EMAIL PROTECTED] writes: Ben Finney wrote: A tuple implies a meaning associated with each position in the sequence (like a record with a positional meaning for each field), a list implies the opposite (a sequence with order but not meaning associated with each position). Explain. Well, since you ask so politely :-) I know tuples as immutable lists ... That's a common misconception. Tuples are intended for use as heterogeneous data structures: every index in the sequence *means* something, a semantic meaning applied to the item at that index. It's for this reason that a tuple is immutable: removing items, inserting them in the middle, etc. would imply that the index doesn't have semantic meaning for the structure, which is not true. Lists are intended for use as homogeneous sequences: not that every value is of the same type, but that a particular index in the sequence doesn't *mean* anything about the semantic interpretation of the item at that position. It's for this reason that a list is mutable: since the index of an item has no semantic meaning, inserting new items or removing them from anywhere in the sequence doesn't alter the meaning of the structure. James Tauber explains further: URL:http://jtauber.com/blog/2006/04/15/python_tuples_are_not_just_constant_lists -- \ You can be a victor without having victims. -- Harriet Woods | `\ | _o__) | Ben Finney -- http://mail.python.org/mailman/listinfo/python-list
Re: Tuples vs Lists: Semantic difference (was: Extract String From Enclosing Tuple)
On Feb 28, 10:45 pm, Ben Finney [EMAIL PROTECTED] wrote: Bjoern Schliessmann [EMAIL PROTECTED] writes: I know tuples as immutable lists ... That's a common misconception. And this catch phrase, that's a common misconception, is a common aping of the BDFL's take on this. As several long threads have shown, it is a highly controversial topic and claiming that one side has misconceived it doesn't make it more true than a Catholic claiming that Protestants are misconceived about the True Christianity or vice versa. Tuples are intended for use as heterogeneous data structures: every index in the sequence *means* something, a semantic meaning applied to the item at that index. It's for this reason that a tuple is immutable: removing items, inserting them in the middle, etc. would imply that the index doesn't have semantic meaning for the structure, which is not true. Lists are intended for use as homogeneous sequences: not that every value is of the same type, but that a particular index in the sequence doesn't *mean* anything about the semantic interpretation of the item at that position. It's for this reason that a list is mutable: since the index of an item has no semantic meaning, inserting new items or removing them from anywhere in the sequence doesn't alter the meaning of the structure. James Tauber explains further: URL:http://jtauber.com/blog/2006/04/15/python_tuples_are_not_just_constan... Nice, that's a good summary of the straw man arguments about the true distinction between tuples and lists. Now can you please explain why an heterogeneous data structure: 1) does not support __setitem__, changing the value of an existing item from 3 to 4, 2) supports iteration over its (heterogeneneous) elements, but not an index() method, and 3) why using indices rather than names for implied semantics is a good idea anyway. As for addition/removal/insertion of elements not making sense for a heterogeneous data structure, have you heard of database schema change ? Heterogeneous data structures are well known for several decades now; they are commonly spelled records though, not tuples, and have a more reasonable API to support their semantics. George -- http://mail.python.org/mailman/listinfo/python-list
