🌐 Mailman 3 May 2023 - Python-list - python.org

An "adapter", superset of an iterator
by fedor tryfanau May 3, 2023

May 3, 2023

I've been using python as a tool to solve competitive programming problems for a while now and I've noticed a feature, python would benefit from having. Consider "reversed(enumerate(a))". This is a perfectly readable code, except it's wrong in the current version of python. That's because enumerate returns an iterator, but reversed can take only a sequence type. The feature I am describing (and proposing) solves this. Introducing an adapter type: this is an iterator, but it's items can be accessed out of order. More formally it has to: 1. Have __getitem__ to allow access by index 2. Have __len__ 3. Be immutable (It is a lot like the sequence protocol) An adapter can be converted to an iterator by accessing it from 0 to len(adapter). Which is done by iter(). (or by __iter__, I don't know which implementation would be "right") ``` iter(a) #is equivalent to (a[i] for i in range(len(a))) ``` For example any tuple is a valid adapter and any list can be easily converted to one. Built-in adapter-generators: "map" function should really return an adapter. ``` #possible implementation m=map(lambda x:x+1,[1,2,3,4,5]) #lambda is not called print(m[3])# gives 5 by calling the lambda on list's 3rd element, which is 4 #simplified implementation class map: def __init__(self,f,a): self.f=f self.a=a def __getitem__(self,idx): return self.f(self.a[idx]) def __len__(self): return len(self.a) ``` enumerate should really return an adapter ``` #simplified implementation class enumerate: def __init__(self,a): self.a = a def __getitem__(self,idx): return idx,self.a[idx] def __len__(self): return len(self.a) ``` reversed should really return an adapter ``` #simplified implementation class reversed: def __init__(self,a): self.a = a self.length=len(a) def __getitem__(self,idx): return self.a[self.length-idx-1] def __len__(self): return self.length ``` zip should really return an adapter range should really return an adapter filter should *not* return an adapter All of those functions return an adapter and take in an adapter. But some (excluding "reversed") should be able take an iterator and return an iterator. So the way I imagine a possible release version to work is that "reversed(enumerate(a))" works if a is an adapter and throws an exception if not Perhaps there should be even an adapter comprehension: ``` Add1 = (a+1 for a) #is equivalent to Add1 = lambda s: map((lambda a: a+1),s) transformed = Add1([1,2,3]) print(transformed[1])# should be 3 ``` This adapter feature also allows you to not use a key argument "key=" for certain functions (which could be non-existing). For example bisect.bisect functions before 3.10 didn't have a key= argument. Some third-party libraries could do this with it's functions too. (Subject to change)

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Re: Editing PEP-8, in particular "expected 2 blanks, found 1
by Roy Hann May 3, 2023

May 3, 2023

Kevin M. Wilson wrote: > Folks, help please! What the @#$! are these doing popping up. Code styles are personal, and not subject to debate. [snip] "Expected 2 blanks"? Or "Expected 2 blank _lines_"? Two blank lines between function/method definitions has been recommended for more than 20 years. When I first started using Python I found a lot of the PEP-8 style recommendations whimsical and annoying. But I've come to appreciate most of them and no longer feel a strong urge to go my own way. I even use black now. There are plenty of seriously bad habits in our industry. I save my individualism for fighting things that are demonstraby harmful. Roy

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Re: Using loguru in a library
by Roy Hann May 2, 2023

May 2, 2023

Dieter Maurer wrote: > Roy Hann wrote at 2023-4-30 15:40 -0000: >>Is there anyone using loguru (loguru 0.5.3 in my case) successfully in a >>library? >> ... >> import mylib >> logger.enable('mylib') >> >>expecting that it would report any log messages above level DEBUG, just >>as it does when I don't disable logging. > > Have you configured the logging system? > > Note that `logging.config.fileConfig` may do strange things > regarding disabling (due to its default parameter > `disable_existing_loggers=True`). > I had several cases of missing log entries because `fileConfig` > had disabled already existing loggers. Thank you for the response Dieter. I am using the loguru package, not the logging package. I think my next step is going to have be creating a minimal test case to post on stackoverflow. :-P Roy

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Editing PEP-8, in particular "expected 2 blanks, found 1
by Kevin M. Wilson May 2, 2023

May 2, 2023

Folks, help please! What the @#$! are these doing popping up. Code styles are personal, and not subject to debate.Where can I edit these out of my IDE? Kevin "When you pass through the waters, I will be with you: and when you pass through the rivers, they will not sweep over you. When you walk through the fire, you will not be burned: the flames will not set you ablaze." Isaiah 43:2 | | Virus-free.www.avg.com |

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Using loguru in a library
by Roy Hann May 2, 2023

May 2, 2023

Is there anyone using loguru (loguru 0.5.3 in my case) successfully in a library? In my __init__.py in mylib I do logger.disable('mylib') which definitely works. I don't get any more logging. I "pip install ." the library, then in mytest.py I do import mylib logger.enable('mylib') expecting that it would report any log messages above level DEBUG, just as it does when I don't disable logging. Unfortunately it doesn't have any effect; it doesn't report any logging from mylib. I have verified that __name__ is visible in the library and is 'mylib'. I would also have expected that logger.enable(None) would turn all the logging on everywhere but it seems not. I have probably misunderstood how logger.enable() is supposed to be used. Can anyone share a brief example? Roy

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Note when migrating '#' formats for PyArgs_ParseTuple
by aapost May 2, 2023

May 2, 2023

Just in case anyone else runs in to it. If you have code such as: char* a; char* b; char* d; int size; if (!PyArg_ParseTuple(args, "sss#:f", &a, &b, &d, &size)) return NULL; and it tells you to: #define PY_SSIZE_T_CLEAN #include "Python.h" Be sure to change int size; to: Py_ssize_t size; If you forget, your code will compile fine and still work perfectly fine on all py2 and py3 i386 variants, but will break 64bit variants in very non-obvious ways. In the above example the mismatched pointer type of size messes up the seemingly unrelated pointer a padr a 0x7f1f00000000 padr b 0x7f1fa656b960 padr d 0x7f1fa65579a0 So while accessing the s# argument works fine, you get a segfault when you access a I spent quite a while chasing my tail researching variadics, picking apart the code trying to understand how and where 'a' gets stomped on before I realized the size type mismatch. -- On that note, I will say that the removal of distutils/setup.py-ability from 3.12 without a similarly simple out of the box replacement is unfortunate. (if setup.py usage had design flaws that lead to deprecation fine, but python should have some form of stand alone equivalency included out of the box by default) For researching issues like the above, and for people who want to use python for off-internet projects, it is nice to be able to spin up a virtual machine from any said era, and do a ./configure make ./python setup.py install --user As things diverge in the future, things start to break, and you don't always have all the pieces to put it back together, and pip kind of sucks and is not simple when it doesn't work. It's pushy, it wants to force everyone to connect to the hive, it demands ssl, etc, when I just want it to shut up and make ./python -m pip install . do what ./python setup.py install --user does I will figure out what works best situationally moving forward as far as work arounds (probably modifying pip), but just saying, the modern way of jenkinizing everything sucks, and takes the fun out of tinkering in a cave.

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Re: Using loguru in a library
by Roy Hann May 2, 2023

May 2, 2023

MRAB wrote: > On 2023-04-30 16:40, Roy Hann wrote: >> Is there anyone using loguru (loguru 0.5.3 in my case) successfully in a >> library? >> >> >> In my __init__.py in mylib I do >> >> logger.disable('mylib') >> >> which definitely works. I don't get any more logging. >> >> I "pip install ." the library, then in mytest.py I do >> >> import mylib >> logger.enable('mylib') >> >> expecting that it would report any log messages above level DEBUG, just >> as it does when I don't disable logging. Unfortunately it doesn't >> have any effect; it doesn't report any logging from mylib. >> >> I have verified that __name__ is visible in the library and is 'mylib'. >> >> I would also have expected that logger.enable(None) would turn all the >> logging on everywhere but it seems not. >> >> I have probably misunderstood how logger.enable() is supposed to be >> used. Can anyone share a brief example? >> > According to the docs, the argument is the name of the module. > > In your example, the name of the module (i.e. file) is "__init__"; > "mylib" is the name of the package. Thanks for taking a look at this. I will continue to play around with it using your suggestion, but according to the snippets and recipes for loguru at https://loguru.readthedocs.io/en/stable/resources/recipes.html#configuring-… I need to refer to the package name in disable() in __init__.py, not the module/file name, and so I expect to use it in enable() in my main. Also, as mentioned, I have already verified that __name__ in my package is referring to the package name not the module. Since every package will have a __init__.py even if it's empty, using the module name to control logging by package would be difficult. Or so I say. My code isn't working so I am wrong about some or all of this. I'll keep tinkering and looking out for advice/suggestions here. Roy

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