Re: Over 30 types of variables available in python ?
On 1-7-2013 2:53:26 AM UTC-6, chaouche yacine wrote: Thanks for all your comments. It appears to me that there is a slight confusion between types and classes then, plus other entities (protocols ?) The only confusion stems from improper terminology. Class is the worst possible word to describe: /the code written by a programmer to define an object/. This epidemic of transforming words improperly is not only a python problem (as you well know). I believe it is high time we stop designing languages by propagating foolish terminology simply because we have no will to break the status quo. And everybody needs to help push this cause along by refusing to use the word class and only use the words object definition. This is something we can all do WITHOUT modifying the python source. This is how you get the snowball rolling. However, if we do this for long enough, language designers will start to realize that class is NOT the proper terminology and MAYBE they will consider terminology a bit more. Well, a boy can dream... We MUST separate the idea of: an object that lives in memory from the: code that defines the object AND we must do so by wielding intuitive terminology. Just because person X decides to jump off a bridge, that action does not impose person Y to blindly follow -- http://mail.python.org/mailman/listinfo/python-list
Re: Over 30 types of variables available in python ?
Thanks for all your comments. It appears to me that there is a slight confusion between types and classes then, plus other entities (protocols ?) So my question is : is there a notion of type in python, like in other languages (integers, booleans, floats, strings, characters (in c)) ? if so, can you give a list of the available types ? The documentation (http://docs.python.org/2/library/stdtypes.html) states The principal built-in types are numerics, sequences, mappings, files, classes, instances and exceptions. From: Terry Reedy tjre...@udel.edu To: python-list@python.org Sent: Monday, January 7, 2013 1:45 AM Subject: Re: Over 30 types of variables available in python ? On 1/6/2013 6:12 PM, chaouche yacine wrote: booleans ints, floats, longs, complexes strings, unicode strings lists, tuples, dictionaries, dictionary views, sets, frozensets, buffers, bytearrays, slices functions, methods, code objects,modules,classes, instances, types, nulls (there is exactly one object of type Null which is None), tracebacks, frames generators, iterators, xranges, files, memoryviews, context managers, These are all listed in this page http://docs.python.org/2/library/stdtypes.html as built-in types. They would better be called classes. Every thing is Python is an instance of a class. 'Iterator' and 'context manager' are protocols that multiple classes can follow, not classes themselves. Am I getting anything wrong here ? I'm a bit confused about it. I have never seen so many types in the few programming languages I saw. C has up to 8 integer types, Python 3 just 1. Most of the above are structures in C, which may or may not by typedef-ed, or classes in C++. If you counted all the structures and classes that come with C or C++, you would find a comparable number. C stdlib has a pointer to file structure type, which is equivalent to Python's file class. It is true that C does not come with hashed arrays (sets) and hashed associative arrays (dicts), but they are often needed. So C programmers either reinvent the wheel or include a third-party library. C also has frame structure, but they are normally hidden. C programmers do not have easy direct access. However, virus writers learn to work with them ;-(. -- Terry Jan Reedy -- http://mail.python.org/mailman/listinfo/python-list-- http://mail.python.org/mailman/listinfo/python-list
Re: Over 30 types of variables available in python ?
On Mon, 07 Jan 2013 00:53:26 -0800, chaouche yacine wrote: Thanks for all your comments. It appears to me that there is a slight confusion between types and classes then, plus other entities (protocols ?) In Python 3, types and classes are synonyms. They mean the same thing. In Python 2, there is a very subtle difference, due to the existence of old style or classic classes, for backward compatibility, which are not identical to new style classes, also known as types. But they are a kind of type -- although there are some differences, you can consider them to be the same sort of thing. So my question is : is there a notion of type in python, like in other languages (integers, booleans, floats, strings, characters (in c)) ? if so, can you give a list of the available types ? Yes, and no. Yes, there is a notation of type in Python which is exactly the same sort of notation of type in other languages, such as C. The difference between C and Python is not in the notation of type, but in the notation of variable or name. In C, *variables* have a type. If you declare a variable x to be a float, then three things happen: * the C compiler creates a fixed memory location and calls it x; * the C compiler interprets the *value* of that memory location (which is actually just a bunch of bytes) as a float; * the C compiler will only ever place values into that memory location if it thinks that the value is a float, or compatible with a float. Because all values are bunches of bytes, you can (with a bit of effort) grab the bytes from any location, without caring what the type the compiler considers it. Sometimes this is useful; more often it is a source of bugs. In Python, *names* have no type, but *objects* (values) do. Because names are untyped, the one name (say, x) might be store a float one minute, then later have a list assigned to it, then a string, then a float again. But at any instant, whatever the value of x, it is an object, and objects always have a type no matter what name they are bound to. The type information is *part of the object*, rather than part of the name. Because Python considers all objects to be typed, there is no concept of extracting the raw bytes from a list. (Of course lists actually are made out of bytes, but you cannot access them from pure Python code.) So, yes, Python has types, just as C has types, but the difference is that Python associates the type with the *value* (object) rather than a storage location (variable). But no, we can't give a complete list of all types, because there is no limit to the number of types. There are a certain number of built-in types, plus many more types which are available from the standard library, plus an infinite number of custom types you can create yourself. You can get a list of the common built-in types and the standard library types from the Fine Manual: http://docs.python.org/2/library/ See also: http://docs.python.org/2/reference/datamodel.html There are also built-in types which are essentially undocumented, and used as implementation details of higher-level objects like functions, methods, and so forth. You are not expected to use these directly. Instead, you just use the function itself. If you are unfamiliar with Object Oriented Programming, you can broadly speaking consider types to be like smart structs that carry code around with them. There is no limit to the number of possible structs, and likewise there is no limit to the number of possible types. The documentation (http://docs.python.org/2/library/stdtypes.html) states The principal built-in types are numerics, sequences, mappings, files, classes, instances and exceptions. Yes, they are the principal types, but there are many others. There are three different built-in numeric types: int long float plus Decimal and Fraction in the standard library; There are two standard built-in sequence types: list tuple plus others in the standard library, such as namedtuple; There is one standard built-in mapping type: dict plus at least two more in the standard library, defaultdict and ordereddict; etc. You can read the docs more easily than I can copy the types out. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
Re: Over 30 types of variables available in python ?
chaouche yacine yacinechaou...@yahoo.com wrote:
booleans
ints, floats, longs, complexes
strings, unicode strings
lists, tuples, dictionaries, dictionary views, sets, frozensets,
buffers, bytearrays, slices functions, methods, code
objects,modules,classes, instances, types, nulls (there is exactly one
object of type Null which is None), tracebacks, frames generators,
iterators, xranges, files,
memoryviews,
context managers,
These are all listed in this page
http://docs.python.org/2/library/stdtypes.html as built-in types. Am I
getting anything wrong here ? I'm a bit confused about it. I have
never seen so many types in the few programming languages I saw.
Instances aren't types (though types themselves are instances): every
object in Python is an instance.
If you want a list of types that exist in your particular copy of Python
then you can print it out easily enough:
def allsubclasses(base):
mod = base.__module__
if mod in ('builtins', '__builtin__', 'exceptions'):
yield getattr(base, '__qualname__', base.__name__)
else:
yield {}.{}.format(base.__module__, getattr(base,
'__qualname__', base.__name__))
for typ in type.__subclasses__(base):
for t in allsubclasses(typ): yield t
all_types = sorted(set(allsubclasses(object)), key=str.lower)
print(len(all_types))
print(all_types)
That won't show any types that haven't been imported, but it gives me
293 types that are all loaded on startup in Python 3.3 and 150 in Python
2.7.
--
http://mail.python.org/mailman/listinfo/python-list
Re: Over 30 types of variables available in python ?
So I guess if one *really* wanted to compare C variables to Python variables, you could say that all python variables are of type void* except Python does all mallocs/frees and the casting for you. -- http://mail.python.org/mailman/listinfo/python-list
Re: Over 30 types of variables available in python ?
On 01/07/2013 09:32 AM, marduk wrote: So I guess if one *really* wanted to compare C variables to Python variables, you could say that all python variables are of type void* except Python does all mallocs/frees and the casting for you. A better analogy would be to C++, and all names would be something like shared_ptrobject*. And (except for old-style classes) all actual data is of a type derived from object. -- DaveA -- http://mail.python.org/mailman/listinfo/python-list
Re: Over 30 types of variables available in python ?
On Tue, Jan 8, 2013 at 1:45 AM, Dave Angel d...@davea.name wrote: On 01/07/2013 09:32 AM, marduk wrote: So I guess if one *really* wanted to compare C variables to Python variables, you could say that all python variables are of type void* except Python does all mallocs/frees and the casting for you. A better analogy would be to C++, and all names would be something like shared_ptrobject*. And (except for old-style classes) all actual data is of a type derived from object. But yes, a C pointer variable is closest to a Python local, with actual content always stored on the heap. ChrisA -- http://mail.python.org/mailman/listinfo/python-list
Re: Over 30 types of variables available in python ?
On Mon, Jan 7, 2013 at 10:12 AM, chaouche yacine yacinechaou...@yahoo.com wrote: booleans ints, floats, longs, complexes strings, unicode strings lists, tuples, dictionaries, dictionary views, sets, frozensets, buffers, bytearrays, slices functions, methods, code objects,modules,classes, instances, types, nulls (there is exactly one object of type Null which is None), tracebacks, frames generators, iterators, xranges, files, memoryviews, context managers, These are all listed in this page http://docs.python.org/2/library/stdtypes.html as built-in types. Am I getting anything wrong here ? I'm a bit confused about it. I have never seen so many types in the few programming languages I saw. Not quite. Python has one type of variable: the name binding. Those are different types of objects. Since you can subclass object to make your own class, there's an infinite number of types available. But the ones you'll be using in most programs are: * boolean, int, float (and long, in Python 2, but in Python 3 that's the same as int) * Unicode strings * In Python 2, bytes strings * lists, tuples, dicts, maybe sets * functions * files The rest, you're unlikely to worry much about. The program will use them under the covers, but you don't need to concern yourself with the details. The only other thing you'll need to look at is the generic handling of object() and, by virtue of subclassing, every other object. ChrisA -- http://mail.python.org/mailman/listinfo/python-list
Re: Over 30 types of variables available in python ?
On 01/06/2013 06:12 PM, chaouche yacine wrote: booleans ints, floats, longs, complexes strings, unicode strings lists, tuples, dictionaries, dictionary views, sets, frozensets, buffers, bytearrays, slices functions, methods, code objects,modules,classes, instances, types, nulls (there is exactly one object of type Null which is None), tracebacks, frames generators, iterators, xranges, files, memoryviews, context managers, These are all listed in this page http://docs.python.org/2/library/stdtypes.html as built-in types. Am I getting anything wrong here ? I'm a bit confused about it. I have never seen so many types in the few programming languages I saw. First, you're describing Python 2.x ;3.x is different in a few ways. For one, int and long are combined into a single type. Variables don't have types. Only objects have types. A name can be bound to any object, regardless of its type, or to what it might have been previously bound. Otherwise, you're right. Python is a rich language, with batteries included. There's a lot in the built-in space, but if you include the stdlib, it's really rich. And if you include the fact that objects you define yourself are first-class, there are very few limits. -- DaveA -- http://mail.python.org/mailman/listinfo/python-list
Re: Over 30 types of variables available in python ?
On 1/6/2013 6:12 PM, chaouche yacine wrote: booleans ints, floats, longs, complexes strings, unicode strings lists, tuples, dictionaries, dictionary views, sets, frozensets, buffers, bytearrays, slices functions, methods, code objects,modules,classes, instances, types, nulls (there is exactly one object of type Null which is None), tracebacks, frames generators, iterators, xranges, files, memoryviews, context managers, These are all listed in this page http://docs.python.org/2/library/stdtypes.html as built-in types. They would better be called classes. Every thing is Python is an instance of a class. 'Iterator' and 'context manager' are protocols that multiple classes can follow, not classes themselves. Am I getting anything wrong here ? I'm a bit confused about it. I have never seen so many types in the few programming languages I saw. C has up to 8 integer types, Python 3 just 1. Most of the above are structures in C, which may or may not by typedef-ed, or classes in C++. If you counted all the structures and classes that come with C or C++, you would find a comparable number. C stdlib has a pointer to file structure type, which is equivalent to Python's file class. It is true that C does not come with hashed arrays (sets) and hashed associative arrays (dicts), but they are often needed. So C programmers either reinvent the wheel or include a third-party library. C also has frame structure, but they are normally hidden. C programmers do not have easy direct access. However, virus writers learn to work with them ;-(. -- Terry Jan Reedy -- http://mail.python.org/mailman/listinfo/python-list
