I am moving the discussion on file-like methods to GitHub. Mailing list is
not very usable IMHO. Please switch to that.
https://github.com/python/peps/issues/66
pozdrawiam,
Arkadiusz Bulski
2016-08-02 7:02 GMT+02:00 <python-ideas-request@python.org>:
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Today's Topics:
1. Re: Trial balloon: adding variable type declarations in
support of PEP 484 (Steven D'Aprano)
2. Re: Trial balloon: adding variable type declarations in
support of PEP 484 (Steven D'Aprano)
3. Re: Proposing new file-like object methods (eryk sun)
4. Re: Trial balloon: adding variable type declarations in
support of PEP 484 (Guido van Rossum)
5. Re: Trial balloon: adding variable type declarations in
support of PEP 484 (Guido van Rossum)
----------------------------------------------------------------------
Message: 1
Date: Tue, 2 Aug 2016 12:55:09 +1000
From: Steven D'Aprano <steve@pearwood.info>
To: python-ideas@python.org
Subject: Re: [Python-ideas] Trial balloon: adding variable type
declarations in support of PEP 484
Message-ID: <20160802025509.GD6608@ando.pearwood.info>
Content-Type: text/plain; charset=us-ascii
On Mon, Aug 01, 2016 at 02:31:16PM -0700, Guido van Rossum wrote:
PEP 484 doesn't change Python's syntax. Therefore it has no good
syntax to offer for declaring the type of variables, and instead you
have to write e.g.
a = 0 # type: float
b = [] # type: List[int]
c = None # type: Optional[str]
I'd like to address this in the future, and I think the most elegant
syntax would be to let you write these as follows:
a: float = 0
b: List[int] = []
c: Optional[str] = None
Those examples look reasonable to me.
[...]
Second, when these occur in a class body, they can define either class
variables or instance variables. Do we need to be able to specify
which?
I would think so. Consider the case that you have Class.spam and
Class().spam which may not be the same type. E.g. the class attribute
(representing the default value used by all instances) might be a
mandatory int, while the instance attribute might be Optional[int].
Third, there's an annoying thing with tuples/commas here. On the one
hand, in a function declaration, we may see (a: int = 0, b: str = '').
On the other hand, in an assignment, we may see
a, b = 0, ''
Suppose we wanted to add types to the latter. Would we write this as
a, b: int, str = 0, ''
or as
a: int, b: str = 0, ''
Require parens around the name:hint.
(a:int), (b:str) = 0, ''
Or just stick to a type hinting comment :-)
What about this case?
spam, eggs = [1, 2.0, 'foo'], (1, '')
[a, b, c], [d, e] = spam, eggs
That becomes:
[(a:int), (b:float), (c:str)], [(x:int), (y:str)] = spam, eggs
which is bearable, but just unpleasant enough to discourage people from
doing it unless they really need to.
--
Steve
------------------------------
Message: 2
Date: Tue, 2 Aug 2016 12:57:12 +1000
From: Steven D'Aprano <steve@pearwood.info>
To: python-ideas@python.org
Subject: Re: [Python-ideas] Trial balloon: adding variable type
declarations in support of PEP 484
Message-ID: <20160802025711.GE6608@ando.pearwood.info>
Content-Type: text/plain; charset=us-ascii
On Tue, Aug 02, 2016 at 07:40:39AM +1000, Chris Angelico wrote:
Additional case, unless it's patently obvious to someone with more 484
experience than I: what happens with chained assignment?
a = b = c = 0
Does each variable get separately tagged, or does one tag apply to all?
(a:int) = (b:Optional[int]) = c = 0
`a` is declared to always be an int, `b` declared to be an int or None,
and `c` is not declared.
--
Steve
------------------------------
Message: 3
Date: Tue, 2 Aug 2016 04:33:53 +0000
From: eryk sun <eryksun@gmail.com>
To: python-ideas@python.org
Subject: Re: [Python-ideas] Proposing new file-like object methods
Message-ID:
<
CACL+1au+bX_tKQvxDJC1SBLSObKbqAUPjj9dpmcr9s1izq0Cng@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
On Tue, Aug 2, 2016 at 2:00 AM, Random832 <random832@fastmail.com> wrote:
On Mon, Aug 1, 2016, at 20:27, Wes Turner wrote:
file.pread?
Wouldn't that be rather like having os.fstatat?
For the concept in general, I'm concerned that the equivalent
functionality on windows may require that the I/O be done
asynchronously, or that the file have been opened in a special
way.
Updating the file position is all or nothing. In synchronous mode,
which is what the CRT's low I/O implementation uses, the file position
is always updated. However, one can atomically set the file position
before a read by passing an overlapped with an offset to ReadFile,
which in turn sets the ByteOffset argument of the underlying
NtReadFile [1] system call.
[1]: https://msdn.microsoft.com/en-us/library/ff567072
For example:
import _winapi
import ctypes
from ctypes import wintypes
kernel32 = ctypes.WinDLL('kernel32', use_last_error=True)
ULONG_PTR = wintypes.WPARAM
class OVERLAPPED(ctypes.Structure):
class _OFF_PTR(ctypes.Union):
class _OFFSET(ctypes.Structure):
_fields_ = (('Offset', wintypes.DWORD),
('OffsetHigh', wintypes.DWORD))
_fields_ = (('_offset', _OFFSET),
('Pointer', wintypes.LPVOID))
_anonymous_ = ('_offset',)
_fields_ = (('Internal', ULONG_PTR),
('InternalHigh', ULONG_PTR),
('_off_ptr', _OFF_PTR),
('hEvent', wintypes.HANDLE))
_anonymous_ = ('_off_ptr',)
with open('test.txt', 'wb') as f:
f.write(b'0123456789')
h = _winapi.CreateFile('test.txt', 0x80000000, 3, 0, 3, 0, 0)
buf = (ctypes.c_char * 5)()
n = (wintypes.DWORD * 1)()
fp = (wintypes.LARGE_INTEGER * 1)()
ov = (OVERLAPPED * 1)()
ov[0].Offset = 5
>>> kernel32.ReadFile(h, buf, 5, n, ov)
1
>>> buf[:]
b'56789'
>>> kernel32.SetFilePointerEx(h, 0, fp, 1)
1
>>> fp[0]
10
Note that after reading 5 bytes at an offset of 5, the current file
position is 10. With pread() it would still be at 0. The file position
can be tracked and set atomically before each read or write, but I
don't think this is practical unless it's part of a larger project to
use the Windows API directly.
------------------------------
Message: 4
Date: Mon, 1 Aug 2016 21:57:12 -0700
From: Guido van Rossum <guido@python.org>
To: "Steven D'Aprano" <steve@pearwood.info>
Cc: Python-Ideas <python-ideas@python.org>
Subject: Re: [Python-ideas] Trial balloon: adding variable type
declarations in support of PEP 484
Message-ID:
<
CAP7+vJJLz2wRPpkrtb8j8v7vTRFqjbw_b4a5pwAv0-5HyKNf4w@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
The parentheses really strike me as too much complexity. You should
just split it up into multiple lines, or use a semicolon.
On Mon, Aug 1, 2016 at 7:57 PM, Steven D'Aprano <steve@pearwood.info>
wrote:
On Tue, Aug 02, 2016 at 07:40:39AM +1000, Chris Angelico wrote:
Additional case, unless it's patently obvious to someone with more 484
experience than I: what happens with chained assignment?
a = b = c = 0
Does each variable get separately tagged, or does one tag apply to all?
(a:int) = (b:Optional[int]) = c = 0
`a` is declared to always be an int, `b` declared to be an int or None,
and `c` is not declared.
--
Steve
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--
--Guido van Rossum (python.org/~guido)
------------------------------
Message: 5
Date: Mon, 1 Aug 2016 22:02:33 -0700
From: Guido van Rossum <guido@python.org>
To: "Steven D'Aprano" <steve@pearwood.info>
Cc: Python-Ideas <python-ideas@python.org>
Subject: Re: [Python-ideas] Trial balloon: adding variable type
declarations in support of PEP 484
Message-ID:
<
CAP7+vJJHYLwzbnOqrbqD3vboktXG-Rp+8n-MYxm8uf_Ge2m_yQ@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
Regarding class variables: in my experience instance variables way
outnumber class variables, except when the latter are used as defaults
for instance variables.
See e.g. this bit of code from mypy (and many others, actually):
https://github.com/python/mypy/blob/master/mypy/nodes.py#L154. All of
these declare instance variables. Many of them have no need for a
default in the class, but must give one anyway or else there's nothing
to put the type comment on -- you can't write
defs # type: List[Statement]
(it would be a NameError) and you certainly don't want to write
defs = [] # type: List[Statement]
(else the gods of shared mutable state will curse you) so you have to
make do with
defs = None # type: List[Statement]
But this would be totally reasonable as
defs: List[Statement]
under my proposal.
On Mon, Aug 1, 2016 at 7:55 PM, Steven D'Aprano <steve@pearwood.info>
wrote:
On Mon, Aug 01, 2016 at 02:31:16PM -0700, Guido van Rossum wrote:
PEP 484 doesn't change Python's syntax. Therefore it has no good
syntax to offer for declaring the type of variables, and instead you
have to write e.g.
a = 0 # type: float
b = [] # type: List[int]
c = None # type: Optional[str]
I'd like to address this in the future, and I think the most elegant
syntax would be to let you write these as follows:
a: float = 0
b: List[int] = []
c: Optional[str] = None
Those examples look reasonable to me.
[...]
Second, when these occur in a class body, they can define either class
variables or instance variables. Do we need to be able to specify
which?
I would think so. Consider the case that you have Class.spam and
Class().spam which may not be the same type. E.g. the class attribute
(representing the default value used by all instances) might be a
mandatory int, while the instance attribute might be Optional[int].
Third, there's an annoying thing with tuples/commas here. On the one
hand, in a function declaration, we may see (a: int = 0, b: str = '').
On the other hand, in an assignment, we may see
a, b = 0, ''
Suppose we wanted to add types to the latter. Would we write this as
a, b: int, str = 0, ''
or as
a: int, b: str = 0, ''
Require parens around the name:hint.
(a:int), (b:str) = 0, ''
Or just stick to a type hinting comment :-)
What about this case?
spam, eggs = [1, 2.0, 'foo'], (1, '')
[a, b, c], [d, e] = spam, eggs
That becomes:
[(a:int), (b:float), (c:str)], [(x:int), (y:str)] = spam, eggs
which is bearable, but just unpleasant enough to discourage people from
doing it unless they really need to.
--
Steve
_______________________________________________
Python-ideas mailing list
Python-ideas@python.org
https://mail.python.org/mailman/listinfo/python-ideas
Code of Conduct: http://python.org/psf/codeofconduct/
--
--Guido van Rossum (python.org/~guido)
------------------------------
Subject: Digest Footer
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------------------------------
End of Python-ideas Digest, Vol 117, Issue 13
*********************************************
Arek Bulski
Chris Angelico