Re: [Python-Dev] Alternative to more ABCs [was:] Iterable String Redux (aka String ABC)
2008/6/1 Guido van Rossum [EMAIL PROTECTED]: The case for String has already been made. Actually I'm not sure. One you know that isinstance(x, String) is true, what can you assume you can do with x? [...] Right. I'm now beginning to wonder what exactly you're after here -- saying that something is an X without saying anything about an API isn't very useful. You need to have at least *some* API to be able to do anything with that knowledge. Apologies to Raymond if I'm putting words into his mouth, but I think it's more about *not* doing things with the type - a String is a Sequence that we don't wish to iterate through (in the flatten case), so the code winds up looking like for elem in seq: if isinstance(elem, Sequence) and not isinstance(elem, String): recurse into the element else: deal with the element as atomic This implies that other empty abstract types aren't useful, though, as they are not subclasses of anything else... Paul. ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] Alternative to more ABCs [was:] Iterable String Redux (aka String ABC)
On Sun, Jun 1, 2008 at 6:57 AM, Paul Moore [EMAIL PROTECTED] wrote: 2008/6/1 Guido van Rossum [EMAIL PROTECTED]: The case for String has already been made. Actually I'm not sure. One you know that isinstance(x, String) is true, what can you assume you can do with x? [...] Right. I'm now beginning to wonder what exactly you're after here -- saying that something is an X without saying anything about an API isn't very useful. You need to have at least *some* API to be able to do anything with that knowledge. Apologies to Raymond if I'm putting words into his mouth, but I think it's more about *not* doing things with the type - a String is a Sequence that we don't wish to iterate through (in the flatten case), so the code winds up looking like for elem in seq: if isinstance(elem, Sequence) and not isinstance(elem, String): recurse into the element else: deal with the element as atomic I thought that was he meant too, until he said he rejected my offhand suggestion of Atomic with these words: Earlier in the thread it was made clear that that atomicity is not an intrinsic property of a type; instead it varies across applications [...] This implies that other empty abstract types aren't useful, though, as they are not subclasses of anything else... There's a thread on this out now I believe. -- --Guido van Rossum (home page: http://www.python.org/~guido/) ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
[Python-Dev] Alternative to more ABCs [was:] Iterable String Redux (aka String ABC)
ISTM, the whole reason people are asking for a String ABC is so you can write isinstance(obj, String) and allow registered
string-like objects to be accepted.
The downside is that everytime you want this for a concrete class or type, it is necessary to write a whole new ABC listing all of
the required methods. Also, you have to change all of the client code's isinstance tests from concrete to abstract.
I propose a simpler approach. Provide an alternative registration function that overrides isinstance() so that objects can
explicitly fake any concrete type:
s = UserString('whiffleball')
print isinstance(s, str)-- False
register_lookalike(UserString, str)
print isinstance(s, str)-- True
Besides saving us from writing tons of new ABCs, the approach works with existing code that already uses isinstance() with concrete
types.
The ABCs that would remain are ones that are truly abstract, that define a generic interface (like mappings and sequences) and ones
that offer some useful mixin behavior. The remaining ABCs are ones where you have a fighting chance of actually being able to
implement the interface (unlike String where it would be darned tricky to fully emulate encode(), split(), etc.)
This would completely eliminate the need for numbers.Integral for example. AFAICT, its sole use case is to provide a way for
numeric's integral types (like int8, int32) to pass themselves off as having the same API as regular ints. Unfortunately, the
current approach requires all consumer code to switch from isinstance(x,int) to isinstance(x,Integral). It would be more useful if
we could simply write register_lookalike(x,int) and be done with it (no need for numbers.py and its attendant abc machinery).
If we don't do this, then String won't be the last request. People will want Datetime for example. Pretty much any concrete type
could have a look-a-like that wanted its own ABC and for all client code to switch from testing concrete types.
Raymond
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Re: [Python-Dev] Alternative to more ABCs [was:] Iterable String Redux (aka String ABC)
I'm willing to meet you halfway. I really don't want isinstance(x,
str) to return True for something that doesn't inherit from the
concrete str type; this is bound to lead to too much confusion and
breakage. But I'm fine with a String ABC (or any other ABC, e.g.
Atomic?) that doesn't define any methods but can be used for type
testing. How about that?
--Guido
On Sat, May 31, 2008 at 5:25 AM, Raymond Hettinger [EMAIL PROTECTED] wrote:
ISTM, the whole reason people are asking for a String ABC is so you can
write isinstance(obj, String) and allow registered string-like objects to be
accepted.
The downside is that everytime you want this for a concrete class or type,
it is necessary to write a whole new ABC listing all of the required
methods. Also, you have to change all of the client code's isinstance tests
from concrete to abstract.
I propose a simpler approach. Provide an alternative registration function
that overrides isinstance() so that objects can explicitly fake any concrete
type:
s = UserString('whiffleball')
print isinstance(s, str)-- False
register_lookalike(UserString, str)
print isinstance(s, str)-- True
Besides saving us from writing tons of new ABCs, the approach works with
existing code that already uses isinstance() with concrete types.
The ABCs that would remain are ones that are truly abstract, that define a
generic interface (like mappings and sequences) and ones that offer some
useful mixin behavior. The remaining ABCs are ones where you have a
fighting chance of actually being able to implement the interface (unlike
String where it would be darned tricky to fully emulate encode(), split(),
etc.)
This would completely eliminate the need for numbers.Integral for example.
AFAICT, its sole use case is to provide a way for numeric's integral types
(like int8, int32) to pass themselves off as having the same API as regular
ints. Unfortunately, the current approach requires all consumer code to
switch from isinstance(x,int) to isinstance(x,Integral). It would be more
useful if we could simply write register_lookalike(x,int) and be done with
it (no need for numbers.py and its attendant abc machinery).
If we don't do this, then String won't be the last request. People will
want Datetime for example. Pretty much any concrete type could have a
look-a-like that wanted its own ABC and for all client code to switch from
testing concrete types.
Raymond
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--Guido van Rossum (home page: http://www.python.org/~guido/)
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Re: [Python-Dev] Alternative to more ABCs [was:] Iterable String Redux (aka String ABC)
Raymond Hettinger wrote: If we don't do this, then String won't be the last request. People will want Datetime for example. Pretty much any concrete type could have a look-a-like that wanted its own ABC and for all client code to switch from testing concrete types. If I remember rightly, the machinery in the ABC's to support registration slows down some other operations with the types - do we want to pay that price all the time? If we do, then it may be a matter of moving some of the registration machinery from ABCMeta up into type itself. Cheers, Nick. -- Nick Coghlan | [EMAIL PROTECTED] | Brisbane, Australia --- http://www.boredomandlaziness.org ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] Alternative to more ABCs [was:] Iterable String Redux (aka String ABC)
On Sat, May 31, 2008 at 6:41 PM, Raymond Hettinger [EMAIL PROTECTED] wrote: From: Guido van Rossum [EMAIL PROTECTED] I'm willing to meet you halfway. I really don't want isinstance(x, str) to return True for something that doesn't inherit from the concrete str type; this is bound to lead to too much confusion and breakage. Probably true. It was an attractive idea though. Unless all client code converts all its isinstance() tests from concrete to abstract, life is going to be tough for people writing look-alike classes which will have limited applicability. I'd rather require that people rewrite their code to benefit from some new piece of functionality than foisting it upon them regardless, breaking some perfectly fine working in the process. This is how we've always done it. But I'm fine with a String ABC (or any other ABC, e.g. Atomic?) that doesn't define any methods but can be used for type testing. How about that? That's progress! It makes abstract substitution possible while still saving us a lot of code and avoiding over-specification. I propose the following empty abstract classes: String, Datetime, Deque, and Socket. Sounds like a mini-PEP is in place. It should focus on the code to actually define these and the intended ways to use them. -1 on Atomic though. Earlier in the thread it was made clear that that atomicity is not an intrinsic property of a type; instead it varies across applications (when flattening email folders, a multi-part mime message is atomic, but when flattening individual messages, a multi-part mime message is just another nested container, part of the tree, not one of the leaves). Fine, it was just an idle thought. Are you open to considering numbers.Integral to be one of the new empty abstract classes? That would make it much easier for objects wanting to pass themselves as integers. As it stands now, an aspiring Integral class is required to implement a number of arcana including: __rxor__, __rrshift__, __pow__, __invert__, __index__, and __long__. I don't think Integer should be completely abstract (what good is an int you can't add 1 to?) but I could be amenable to reducing the set of required operations (which could then resurface as a separate ABC). Please write another mini-PEP. Where did you see __long__? That seems a mistake (at least in 3.0). -- --Guido van Rossum (home page: http://www.python.org/~guido/) ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] Alternative to more ABCs [was:] Iterable String Redux (aka String ABC)
From: Guido van Rossum [EMAIL PROTECTED] I'm willing to meet you halfway. I really don't want isinstance(x, str) to return True for something that doesn't inherit from the concrete str type; this is bound to lead to too much confusion and breakage. Probably true. It was an attractive idea though. Unless all client code converts all its isinstance() tests from concrete to abstract, life is going to be tough for people writing look-alike classes which will have limited applicability. But I'm fine with a String ABC (or any other ABC, e.g. Atomic?) that doesn't define any methods but can be used for type testing. How about that? That's progress! It makes abstract substitution possible while still saving us a lot of code and avoiding over-specification. I propose the following empty abstract classes: String, Datetime, Deque, and Socket. -1 on Atomic though. Earlier in the thread it was made clear that that atomicity is not an intrinsic property of a type; instead it varies across applications (when flattening email folders, a multi-part mime message is atomic, but when flattening individual messages, a multi-part mime message is just another nested container, part of the tree, not one of the leaves). Are you open to considering numbers.Integral to be one of the new empty abstract classes? That would make it much easier for objects wanting to pass themselves as integers. As it stands now, an aspiring Integral class is required to implement a number of arcana including: __rxor__, __rrshift__, __pow__, __invert__, __index__, and __long__. Raymond ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] Alternative to more ABCs [was:] Iterable String Redux (aka String ABC)
[Raymond] I propose the following empty abstract classes: String, Datetime, Deque, and Socket. [GvR] Sounds like a mini-PEP is in place. It should focus on the code to actually define these and the intended ways to use them. Okay, will run a Google code search to see if real code exists that runs isinstance tests on the concrete types. Since the new classes are very lightweight (completely empty), these probably only need minimal justification. The case for String has already been made. And the concept of a Socket is already fully abstract. Not sure I really care about Deque. The Datetime.class is tricky. The existence of many implementations of date/time routines indicates that there is a need; however, they don't share the API so they likely won't fit under a common umbrella. Are you open to considering numbers.Integral to be one of the new empty abstract classes? That would make it much easier for objects wanting to pass themselves as integers. As it stands now, an aspiring Integral class is required to implement a number of arcana including: __rxor__, __rrshift__, __pow__, __invert__, __index__, and __long__. I don't think Integer should be completely abstract (what good is an int you can't add 1 to?) but I could be amenable to reducing the set of required operations (which could then resurface as a separate ABC). Please write another mini-PEP. Okay. Will propose to remove the bit flipping methods and anything else that doesn't seem essential to integeriness. Will take a look at the integral types in numeric to see what that actually implement. Where did you see __long__? That seems a mistake (at least in 3.0). It's the first listed abstract method in the Py2.6 code. Raymond ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] Alternative to more ABCs [was:] Iterable String Redux (aka String ABC)
On Sat, May 31, 2008 at 8:09 PM, Raymond Hettinger [EMAIL PROTECTED] wrote: [Raymond] I propose the following empty abstract classes: String, Datetime, Deque, and Socket. [GvR] Sounds like a mini-PEP is in place. It should focus on the code to actually define these and the intended ways to use them. Okay, will run a Google code search to see if real code exists that runs isinstance tests on the concrete types. I wasn't asking for existing code -- I was asking for the code you propose to add to abc.py (or wherever). Since the new classes are very lightweight (completely empty), these probably only need minimal justification. Again, in a mini-PEP I'm not so much looking for justification but for a precise spec. The case for String has already been made. Actually I'm not sure. One you know that isinstance(x, String) is true, what can you assume you can do with x? And the concept of a Socket is already fully abstract. Can you elaborate? There's a very specific API that is assumed of sockets. The code that creates sockets is usually pretty close to the code that consumes it. There are some major classes that cut right through the APIs though: connection or listening (the latter being something on which you call accept()), stream or datagram, and as a special case of stream SSL and the like. Not sure I really care about Deque. The Datetime.class is tricky. The existence of many implementations of date/time routines indicates that there is a need; however, they don't share the API so they likely won't fit under a common umbrella. Right. I'm now beginning to wonder what exactly you're after here -- saying that something is an X without saying anything about an API isn't very useful. You need to have at least *some* API to be able to do anything with that knowledge. Are you open to considering numbers.Integral to be one of the new empty abstract classes? That would make it much easier for objects wanting to pass themselves as integers. As it stands now, an aspiring Integral class is required to implement a number of arcana including: __rxor__, __rrshift__, __pow__, __invert__, __index__, and __long__. I don't think Integer should be completely abstract (what good is an int you can't add 1 to?) but I could be amenable to reducing the set of required operations (which could then resurface as a separate ABC). Please write another mini-PEP. Okay. Will propose to remove the bit flipping methods and anything else that doesn't seem essential to integeriness. Will take a look at the integral types in numeric to see what that actually implement. Where did you see __long__? That seems a mistake (at least in 3.0). It's the first listed abstract method in the Py2.6 code. That actually makes sense -- correct interoperability with longs probably requires that. -- --Guido van Rossum (home page: http://www.python.org/~guido/) ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
