Is a list an instance of a class?

**Dan Bishop** · Jul 18 '05, 05:38 PM

Re: Is a list an instance of a class?

Kent Johnson <kent3737@yahoo .com> wrote in message news:<4197c013$ 1_1@newspeer2.t ds.net>...[color=blue]
> In the Python tutorial section 9.1, it says, "the word ``object'' in
> Python does not necessarily mean a class instance. Like C++ and
> Modula-3, and unlike Smalltalk, not all types in Python are classes: the
> basic built-in types like integers and lists are not, and even somewhat
> more exotic types like files aren't."
>
> Is this still correct or was it made obsolete by Python 2.2? Lists and
> files have __class__ attributes, at least:[/color]

For all practical purposes, it's obsolete. You can inherit from "non-classes" now.
[color=blue][color=green][color=darkred]
>>> class TallyMarks(int) :[/color][/color][/color]
.... def __repr__(self):
.... return 'I' * self
....[color=blue][color=green][color=darkred]
>>> TallyMarks(12)[/color][/color][/color]
IIIIIIIIIIII

[color=blue][color=green][color=darkred]
> >>> [].__class__[/color][/color]
> <type 'list'>[color=green][color=darkred]
> >>> f = open('ThreadQue ue.py')
> >>> f.__class__[/color][/color]
> <type 'file'>
>
> So do integers and floats, though you have to ask nicely for an int:[color=green][color=darkred]
> >>> 1.__class__[/color][/color]
> File "<stdin>", line 1
> 1.__class__
> ^
> SyntaxError: invalid syntax[color=green][color=darkred]
> >>> x=1
> >>> x.__class__[/color][/color]
> <type 'int'>[/color]

You don't have to ask *that* nicely.
[color=blue][color=green][color=darkred]
>>> 1 .__class__ # notice the space[/color][/color][/color]
<type 'int'>

**Steven Bethard** · Jul 18 '05, 05:39 PM

int literals and __class__ (WAS: Is a list an instance of a class?)

Dan Bishop <danb_83 <at> yahoo.com> writes:[color=blue]
> You don't have to ask *that* nicely.
>[color=green][color=darkred]
> >>> 1 .__class__ # notice the space[/color][/color]
> <type 'int'>[/color]

Why does this work? Or, perhaps my real question is why *doesn't* it work
without the space? Pointers to the appropriate point in the docs would be
fine... I assume it's something about making parsing easier...?

Thanks,

Steve

**Erik Max Francis** · Jul 18 '05, 05:39 PM

Re: int literals and __class__ (WAS: Is a list an instance of a class?)

Steven Bethard wrote:
[color=blue]
> Why does this work? Or, perhaps my real question is why *doesn't* it work
> without the space? Pointers to the appropriate point in the docs would be
> fine... I assume it's something about making parsing easier...?[/color]

It's because otherwise it's confusing it for a floating point literal.
All you need to do is put a break so that the parser can't get confused.
1 ._class__ or (1).__class__ will work just fine.

--
Erik Max Francis && max@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis
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-- H.L. Mencken

**Alex Martelli** · Jul 18 '05, 05:39 PM

Re: int literals and __class__

Steven Bethard <steven.bethard @gmail.com> wrote:
[color=blue]
> Dan Bishop <danb_83 <at> yahoo.com> writes:[color=green]
> > You don't have to ask *that* nicely.
> >[color=darkred]
> > >>> 1 .__class__ # notice the space[/color]
> > <type 'int'>[/color]
>
> Why does this work? Or, perhaps my real question is why *doesn't* it work
> without the space? Pointers to the appropriate point in the docs would be
> fine... I assume it's something about making parsing easier...?[/color]

It's to make lexing more predictable: it's known as maximal-much lexing
(without backtracking: backtracking in lexical analysis would really but
really be bad). '1.' (no space) is a token (stands for a float
literal). So, '1.__class__' is two tokens: float '1.' followed by
identified '__class__'.

Alex

**Steve Holden** · Jul 18 '05, 05:39 PM

Re: int literals and __class__ (WAS: Is a list an instance of a class?)

Steven Bethard wrote:
[color=blue]
> Dan Bishop <danb_83 <at> yahoo.com> writes:
>[color=green]
>>You don't have to ask *that* nicely.
>>
>>[color=darkred]
>>>>>1 .__class__ # notice the space[/color]
>>
>><type 'int'>[/color]
>
>
> Why does this work? Or, perhaps my real question is why *doesn't* it work
> without the space? Pointers to the appropriate point in the docs would be
> fine... I assume it's something about making parsing easier...?
>
> Thanks,
>
> Steve
>[/color]
Yup, it's because a dot immediately following an integer would be parsed
(strictly "lexed", I suppose) as a floating point constant,m aking the
__class__ a syntax error.

regards
Steve
--

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**Russell Blau** · Jul 18 '05, 05:39 PM

Re: int literals and __class__ (WAS: Is a list an instance of a class?)

"Steve Holden" <steve@holdenwe b.com> wrote in message
news:_qmmd.1065 9$nj.4248@laker ead01...[color=blue]
> Steven Bethard wrote:
>[color=green]
> > Dan Bishop <danb_83 <at> yahoo.com> writes:
> >[color=darkred]
> >>>>>1 .__class__ # notice the space
> >>
> >><type 'int'>[/color]
> >
> > Why does this work? Or, perhaps my real question is why *doesn't* it[/color][/color]
work[color=blue][color=green]
> > without the space? Pointers to the appropriate point in the docs would[/color][/color]
be[color=blue][color=green]
> > fine... I assume it's something about making parsing easier...?
> >[/color]
> Yup, it's because a dot immediately following an integer would be parsed
> (strictly "lexed", I suppose) as a floating point constant,m aking the
> __class__ a syntax error.
>
> regards
> Steve[/color]

And, in case anyone was wondering (as I was), the following works, too,
despite the fact that it looks incredibly odd:
[color=blue][color=green][color=darkred]
>>> print 1. .__class__[/color][/color][/color]
<type 'float'>

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I don't actually read my hotmail account, but you can replace hotmail with
excite if you really want to reach me.

Is a list an instance of a class?

Is a list an instance of a class?

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