Mailman 3 April 2001 - Python-Dev

RE: [Python-Dev] Those import related syntax errors again...
by Samuele Pedroni 23 Feb '05

23 Feb '05

Hi. [Mark Hammond] > The point isn't about my suffering as such. The point is more that > python-dev owns a tiny amount of the code out there, and I don't believe we > should put Python's users through this. > > Sure - I would be happy to "upgrade" all the win32all code, no problem. I > am also happy to live in the bleeding edge and take some pain that will > cause. > > The issue is simply the user base, and giving Python a reputation of not > being able to painlessly upgrade even dot revisions. I agree with all this. [As I imagined explicit syntax did not catch up and would require lot of discussions.] [GvR] > > Another way is to use special rules > > (similar to those for class defs), e.g. having > > > > <frag> > > y=3 > > def f(): > > exec "y=2" > > def g(): > > return y > > return g() > > > > print f() > > </frag> > > > > # print 3. > > > > Is that confusing for users? maybe they will more naturally expect 2 > > as outcome (given nested scopes). > > This seems the best compromise to me. It will lead to the least > broken code, because this is the behavior that we had before nested > scopes! It is also quite easy to implement given the current > implementation, I believe. > > Maybe we could introduce a warning rather than an error for this > situation though, because even if this behavior is clearly documented, > it will still be confusing to some, so it is better if we outlaw it in > some future version. > Yes this can be easy to implement but more confusing situations can arise: <frag> y=3 def f(): y=9 exec "y=2" def g(): return y return y,g() print f() </frag> What should this print? the situation leads not to a canonical solution as class def scopes. or <frag> def f(): from foo import * def g(): return y return g() print f() </frag> [Mark Hammond] > > This probably won't be a very popular suggestion, but how about pulling > > nested scopes (I assume they are at the root of the problem) > > until this can be solved cleanly? > > Agreed. While I think nested scopes are kinda cool, I have lived without > them, and really without missing them, for years. At the moment the cure > appears worse then the symptoms in at least a few cases. If nothing else, > it compromises the elegant simplicity of Python that drew me here in the > first place! > > Assuming that people really _do_ want this feature, IMO the bar should be > raised so there are _zero_ backward compatibility issues. I don't say anything about pulling nested scopes (I don't think my opinion can change things in this respect) but I should insist that without explicit syntax IMO raising the bar has a too high impl cost (both performance and complexity) or creates confusion. [Andrew Kuchling] > >Assuming that people really _do_ want this feature, IMO the bar should be > >raised so there are _zero_ backward compatibility issues. > > Even at the cost of additional implementation complexity? At the cost > of having to learn "scopes are nested, unless you do these two things > in which case they're not"? > > Let's not waffle. If nested scopes are worth doing, they're worth > breaking code. Either leave exec and from..import illegal, or back > out nested scopes, or think of some better solution, but let's not > introduce complicated backward compatibility hacks. IMO breaking code would be ok if we issue warnings today and implement nested scopes issuing errors tomorrow. But this is simply a statement about principles and raised impression. IMO import * in an inner scope should end up being an error, not sure about 'exec's. We will need a final BDFL statement. regards, Samuele Pedroni.

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Removing doc/howto on python.org
by Andrew Kuchling 29 May '01

29 May '01

Looking at a bug report Fred forwarded, I realized that after py-howto.sourceforge.net was set up, www.python.org/doc/howto was never changed to redirect to the SF site instead. As of this afternoon, that's now done; links on www.python.org have been updated, and I've added the redirect. Question: is it worth blowing away the doc/howto/ tree now, or should it just be left there, inaccessible, until work on www.python.org resumes? --amk

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nested scopes and global: some corner cases
by Samuele Pedroni 28 May '01

28 May '01

Hi. Writing nested scopes support for jython (now it passes test_scope and test_future <wink>), I have come across these further corner cases for nested scopes mixed with global decl, I have tried them with python 2.1b1 and I wonder if the results are consistent with the proposed rule: a free variable is bound according to the nearest outer scope binding (assign-like or global decl), class scopes (for backw-comp) are ignored wrt this. (I) from __future__ import nested_scopes x='top' def ta(): global x def tata(): exec "x=1" in locals() return x # LOAD_NAME return tata print ta()() prints 1, I believed it should print 'top' and a LOAD_GLOBAL should have been produced. In this case the global binding is somehow ignored. Note: putting a global decl in tata xor removing the exec make tata deliver 'top' as I expected (LOAD_GLOBALs are emitted). Is this a bug or I'm missing something? (II) from __future__ import nested_scopes x='top' def ta(): x='ta' class A: global x def tata(self): return x # LOAD_GLOBAL return A print ta()().tata() # -> 'top' should not the global decl in class scope be ignored and so x be bound to x in ta, resulting in 'ta' as output? If one substitutes global x with x='A' that's what happens. Or only local binding in class scope should be ignored but global decl not? regards, Samuele Pedroni

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Import hook to do end-of-line conversion?
by Jack Jansen 23 May '01

23 May '01

[Oops, try again] There's talk on the PythonMac-SIG to create an import hook that would read modules with either \r, \n or \r\n newlines and convert them to the local convention before feeding them to the rest of the import machinery. The reason this has become interesting is the mixed unixness/macness of MacOSX, where such an import hook could be used to share a Python tree between MacPython and bsd-Python. They would only need a different site.py (probably), living somehwere near the head of sys.path, that would be in local end of line convention and enable the hook. However, it seem that such a module would have a much more general scope, for instance if you're accessing samba partitions from windows, or other foreign file systems, etc. Does this sound like a good idea? And (even better:-) has anyone done this already? Would it be of enough interest to include it in the core Lib? -- Jack Jansen | ++++ stop the execution of Mumia Abu-Jamal ++++ Jack.Jansen(a)oratrix.com | ++++ if you agree copy these lines to your sig ++++ www.oratrix.nl/~jack | ++++ see http://www.xs4all.nl/~tank/ ++++

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Unicode and the Windows file system.
by Mark Hammond 02 May '01

02 May '01

I understand the issue of "default Unicode encoding" is a loaded one, however I believe with the Windows' file system we may be able to use a default. Windows provides 2 versions of many functions that accept "strings" - one that uses "char *" arguments, and another using "wchar *" for Unicode. Interestingly, the "char *" versions of function almost always support "mbcs" encoded strings. To make Python work nicely with the file system, we really should handle Unicode characters somehow. It is not too uncommon to find the "program files" or the "user" directory have Unicode characters in non-english version of Win2k. The way I see it, to fix this we have 2 basic choices when a Unicode object is passed as a filename: * we call the Unicode versions of the CRTL. * we auto-encode using the "mbcs" encoding, and still call the non-Unicode versions of the CRTL. The first option has a problem in that determining what Unicode support Windows 95/98 have may be more trouble than it is worth. Sticking to purely ascii versions of the functions means that the worst thing that can happen is we get a regular file-system error if an mbcs encoded string is passed on a non-Unicode platform. Does anyone have any objections to this scheme or see any drawbacks in it? If not, I'll knock up a patch... Mark.

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Slight wart in __all__
by Mark Hammond 01 May '01

01 May '01

I just got caught out by this: """ def foo(): pass __all__ = [foo] """ Then at the interactive prompt: >>> from foo import * Traceback (most recent call last): File "<stdin>", line 1, in ? TypeError: attribute name must be string The problem is that __all__ contains a function object rather than a string object. I had to use the debugger to determine why I was getting the failure :( All you 2.1 veterans will immediately pick that it should read '__all__ = ["foo"]' Looking at the __all__ code: if (skip_leading_underscores && PyString_Check(name) && PyString_AS_STRING(name)[0] == '_') { Py_DECREF(name); continue; } value = PyObject_GetAttr(v, name); PyObject_GetAttr explicitly handles string and unicode objects. However, code here won't like Unicode that much :) Would it make sense to a explicitly raise a more meaningful exception here if __all__ doesnt contain strings?

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Importing extensions on Windows 95
by M.-A. Lemburg 01 May '01

01 May '01

Rebooting the thread... While testing mxNumber, I discovered what looks like a bug in Win95: both Thomas Heller and I are seeing a problem with Python 2.1 when importing extension modules which rely on other DLLs as library. Interestingly, the problem only shows up when starting Python from the installation directory. Looking at the imports using python -vv shows that in this situation, Python tries to import modules, packages, extensions etc. using *relative* paths. Now, under Win98 there is no problem, but Win95 doesn't seem to like these relative imports when it comes to .pyd files which reference DLLs in the same directory. It doesn't have any problems when Python is started outside the installation dir, since in that case Python uses absolute paths for importing modules and extensions. Would it be hard to tweak Python into always using absolute search paths during module import ? -- Marc-Andre Lemburg ______________________________________________________________________ Company & Consulting: http://www.egenix.com/ Python Software: http://www.lemburg.com/python/

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Iterators, map, xreadlines and docs
by Tim Peters 30 Apr '01

30 Apr '01

A confused user on c.l.py reported that while for x in file.xreadlines(): works fine, map(whatever, file.xreadlines()) blows up with TypeError: argument 2 to map() must be a sequence object The docs say both contexts require "a sequence", so this is baffling to them. It's apparently because map() internally insists that the sq_length slot be non-null (but it's null in the xreadlines object), despite that map() doesn't use it for anything other than *guessing* a result size (it keeps going until IndexError is raised regardless of what len() returns, growing or shrinking the preallocated result list as needed). I think that's a bug in map(). Anyone disagree? If so, fine, map() has to be changed to work with iterators anyway <wink>. How are we going to identify all the places that need to become iterator-aware, get all the code changed, and update the docs to match? In effect, a bunch of docs for arguments need to say, in some words or other, that the args must implement the iterator interface or protocol. I think it's essential that we define the latter only once. But the docs don't really define any interfaces/protocols now, so it's unclear where to put that. Fred, Pronounce. Better sooner than later, else I bet a bunch of code changes will get checked in without appropriate doc changes, and the 2.2 docs won't match the code.

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Re: [Python-checkins] CVS: python/dist/src/Python bltinmodule.c,2.198,2.199
by Moshe Zadka 28 Apr '01

28 Apr '01

On Sat, 28 Apr 2001, Tim Peters <tim_one(a)users.sourceforge.net> wrote: > Modified Files: > bltinmodule.c > Log Message: > Fix buglet reported on c.l.py: map(fnc, file.xreadlines()) blows up. > Also a 2.1 bugfix candidate (am I supposed to do something with those?). > Took away map()'s insistence that sequences support __len__, and cleaned > up the convoluted code that made it *look* like it really cared about > __len__ (in fact the old ->len field was only *used* as a flag bit, as > the main loop only looked at its sign bit, setting the field to -1 when > IndexError got raised; renamed the field to ->saw_IndexError instead). Can anyone give me his opinion about whether 2.0.1 should have this bug fix? It's not just for file.xreadlines(): the older fileinput.fileinput() is hurt by this as well... -- "I'll be ex-DPL soon anyway so I'm |LUKE: Is Perl better than Python? looking for someplace else to grab power."|YODA: No...no... no. Quicker, -- Wichert Akkerman (on debian-private)| easier, more seductive. For public key, finger moshez(a)debian.org |http://www.{python,debian,gnu}.org

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SF changing directory structure
by Martin v. Loewis 28 Apr '01

28 Apr '01

> Nobody is in charge: if you know of a problem, please fix it. All > the HTML stuff is under CVS control, and all Python project members > have commit access for it, same as for everything else in the Python > source tree; it's just under the nondist branch instead of the dist > branch. Ok, changed in CVS. Is the answer to SF-FAQ question 1.3 still correct? That modified files have to manually uploaded to SF? That answer does not mention nondist/sf-html at all... Regards, Martin

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