On Thu, Apr 2, 2020 at 8:22 AM Abdur-Rahmaan Janhangeer < arj.python@gmail.com> wrote:

Thanks for the snippet,

Was wondering if given as a package option, we might display the module's help info.

That's what help() is for. The __repr__ is meant to help during development with some succinct representation of the object (hence why they typically have an identifier to help tell equal objects apart). Including docstrings and such is not a goal for the repr and would make it no longer succinct. -Brett

On Fri, Apr 3, 2020 at 7:30 AM Abdur-Rahmaan Janhangeer <arj.python@gmail.com> wrote:

Kind Regards,

Abdur-Rahmaan Janhangeer compileralchemy.com | github Mauritius

On Thu, Apr 2, 2020 at 9:52 PM Brett Cannon <brett@python.org> wrote:

...

That's what help() is for. The __repr__ is meant to help during development with some succinct representation of the object (hence why they typically have an identifier to help tell equal objects apart). Including docstrings and such is not a goal for the repr and would make it no longer succinct.

This means we have a __repr__ option in packages (Without Steven's snippet above)?

You can mess with anything on a module if you subclass ModuleType and stick your one into sys.modules. However, I'm not going to give you the code, because I don't believe in helping people to do bad things :) Use help, not repr. ChrisA

This prints modname.__doc__ / help(modname) / inspect.getdoc(modname) with IPython / Jupyter + ipykernel:

...

...

modname?

This prints something like inspect.getsource(modname)

...

...

modname??

https://ipython.readthedocs.io/en/stable/interactive/python-ipython-diff.htm... https://docs.python.org/3/library/inspect.html If an object defines a _repr_pretty_() method, IPython will call that instead of __repr__() https://ipython.readthedocs.io/en/stable/config/integrating.html#rich-displa... On Thu, Apr 2, 2020, 4:30 PM Abdur-Rahmaan Janhangeer <arj.python@gmail.com> wrote:

Kind Regards,

Abdur-Rahmaan Janhangeer compileralchemy.com <https://www.compileralchemy.com> | github <https://github.com/Abdur-rahmaanJ/> Mauritius

On Thu, Apr 2, 2020 at 9:52 PM Brett Cannon <brett@python.org> wrote:

...

That's what help() is for. The __repr__ is meant to help during development with some succinct representation of the object (hence why they typically have an identifier to help tell equal objects apart). Including docstrings and such is not a goal for the repr and would make it no longer succinct.

This means we have a __repr__ option in packages (Without Steven's snippet above)? _______________________________________________ Python-ideas mailing list -- python-ideas@python.org To unsubscribe send an email to python-ideas-leave@python.org https://mail.python.org/mailman3/lists/python-ideas.python.org/ Message archived at https://mail.python.org/archives/list/python-ideas@python.org/message/EIS67L... Code of Conduct: http://python.org/psf/codeofconduct/

On Fri, Apr 03, 2020 at 08:00:38AM +1100, Steven D'Aprano wrote:

But I can tell you that this will 99.999999% be rejected. And if it is accepted, I can tell you that the first time you get hit by a massive wall of text from a package docstring in an exception or some other use of repr(), you will likely regret the change.

For what it's worth, I just looked at a few of my private packages, half of them have got docstrings that are > a page long, and one has a three page docstring. Perhaps it's time for me to extract some of that into an external file... Personally, I might make and use a display hood to show the first line of a module docstring. That might be useful, I'm willing to try it for a few weeks and see if I like it. But I definitely don't want the entire docstring displayed, and I even more don't want it in the module repr(). -- Steven

I think there's been some confusion with regard to this idea, leading to a combination of technical details vs the merits of the idea. So I'm going to summarize a bit what I think the discussion has yielded: Technical issues: The __repr__ and __str__ are defined on the class, not instances of a class. You cannot override them in an instance. modules are instances of the module class. Thus the only way to change the __repr__ or __str__ (or other magic methods) is to create a custom subclass of the module class. Design issues: You probably don't want to change the __repr__ of a module anyway -- there are good reasons to keep the repr of all modules the same and standardized. (which is one reason __repr__'s are defined on the class, not the instance, you generally wouldn't want different instances of classes to have different __repr__s (or any other different magic method behavior). And while customizing the __repr__ of a module to be non standard is a bad idea, it's not such a bad idea to customize the __str__ of a module -- traditionally that's where you put a more human-readable version of an object. But: modules are kind of special: in the VAST majority of the time, the instances are created by the import mechanism, which the user has little control over. And the writer of the module even less. In many cases, one could write a custom subclass of a standard type, and have your code run that instead of the usual type, and your users would get that custom class, but it's difficult to do that with modules. You can define a custom module class by subclassing types.ModuleType. And you could put that custom module in a __init__.py of a package, and then be able to do: from the_package import the_module and then the_module will have a custom __str__ Here that is, in action: in module_str/__init__.py: import types class StrModule(types.ModuleType): def __init__(self, name, custom_str): super().__init__(name) self.___str__ = custom_str def __str__(self): return f"module {self.__name__}: {self.___str__}" # create a new module with a custom string representation: a_module = StrModule("a_module", "a custom str() for a_module" ) # put a few things into it a_module.x = 5 def a_function(): return "a_function was called" a_module.a_function = a_function the use it: """ test code for a custom string module """ from module_str import a_module print("the repr of the module:", repr(a_module)) print("the str of the module:", str(a_module)) print("and it works:") print(a_module.x) print(a_module.a_function()) Which when run: $ python try_module_str.py the repr of the module: <module 'a_module'> the str of the module: module a_module: a custom str() for a_module and it works: 5 a_function was called If one really wanted to do this, you could populate the module with the contents of a another regular module, so that you'd only need to do this special trick in the __init__, and the rest of your module writing would be the same. However, I can't figure out how to provide a custom __str__ for a package (i.e. the __init__ itself) that could be imported in the regular way. So: you can, with standard Python, make modules (if not packages) with a custom str() ( or repr(), but it seems there is consensus that that's not a good idea). But it's pretty awkward. So if folks think it's a good idea to allow modules to have a custom __str__: it would be nice to add that feature to Python. I'm not saying I advocate for that -- but it's not completely unreasonable. -CHB -- Christopher Barker, PhD Python Language Consulting - Teaching - Scientific Software Development - Desktop GUI and Web Development - wxPython, numpy, scipy, Cython

__doc__ https://docs.python.org/3/library/pydoc.html describes the help() function; which you can also call with: $ pydoc modname $ python -m pydoc modname IPython:

...

...

help(modname)

...

...

?modname modname?

...

...

!pydoc modname !python -m pydoc modname

https://ipython.readthedocs.io/en/stable/interactive/python-ipython-diff.htm... On Fri, Apr 3, 2020, 4:28 PM Chris Angelico <rosuav@gmail.com> wrote:

On Sat, Apr 4, 2020 at 7:02 AM Christopher Barker <pythonchb@gmail.com> wrote:

...

So if folks think it's a good idea to allow modules to have a custom __str__: it would be nice to add that feature to Python.

I'm not saying I advocate for that -- but it's not completely unreasonable.

It's not unreasonable, I agree. But it's also unnecessary. In theory, PEP 562 could have gone for a broader recommendation eg "any dunder on a module will be looked up in the instance", but in practice, which ones are you actually going to need? PEP 562 chose two (__getattr__ and __dir__), with definite use-cases for each. There's no need to override __new__/__init__, since the module body serves that purpose. Comparisons (__lt__ etc) don't make a lot of sense. Modules are generally singletons, so __hash__ and __eq__ aren't needed (the default of using object identity is fine).

There is *one* other dunder that I can imagine getting some good use, and that's __call__. A few others might have occasional uses (maybe __setattr__ for deprecation warnings, same as __getattr__, and maybe __enter__/__exit__ so the module itself can be a context manager), but they would be rather more rare. Changing the repr/str of a module would also be pretty unusual.

Fortunately, the unusual case IS possible - just not as easy. You subclass the module type, instantiate your subclass, and shove the instance into sys.modules. So if you really do need to mess with the repr of your module, you can, even if it's a package :)

ChrisA _______________________________________________ Python-ideas mailing list -- python-ideas@python.org To unsubscribe send an email to python-ideas-leave@python.org https://mail.python.org/mailman3/lists/python-ideas.python.org/ Message archived at https://mail.python.org/archives/list/python-ideas@python.org/message/UDPYBE... Code of Conduct: http://python.org/psf/codeofconduct/

IDK what you'd grep for in these; if it's not there you could send a PR that adds more greppable keywords or cross-:ref:'s the sys.displayhook docs like this: :func:`sys.displayhook` https://docs.python.org/3/library/sys.html#sys.displayhook https://github.com/python/cpython/blob/master/Doc/library/sys.rst ```rst .. function:: displayhook(value) If *value* is not ``None``, this function prints ``repr(value)`` to ``sys.stdout``, and saves *value* in ``builtins._``. If ``repr(value)`` is not encodable to ``sys.stdout.encoding`` with ``sys.stdout.errors`` error handler (which is probably ``'strict'``), encode it to ``sys.stdout.encoding`` with ``'backslashreplace'`` error handler. ``sys.displayhook`` is called on the result of evaluating an :term:`expression` entered in an interactive Python session. The display of these values can be customized by assigning another one-argument function to ``sys.displayhook``. Pseudo-code:: def displayhook(value): if value is None: return # Set '_' to None to avoid recursion builtins._ = None text = repr(value) try: sys.stdout.write(text) except UnicodeEncodeError: bytes = text.encode(sys.stdout.encoding, 'backslashreplace') if hasattr(sys.stdout, 'buffer'): sys.stdout.buffer.write(bytes) else: text = bytes.decode(sys.stdout.encoding, 'strict') sys.stdout.write(text) sys.stdout.write("\n") builtins._ = value .. versionchanged:: 3.2 Use ``'backslashreplace'`` error handler on :exc:`UnicodeEncodeError`. ``` https://github.com/python/cpython/blob/master/Doc/library/pprint.rst https://github.com/python/cpython/blob/master/Doc/library/reprlib.rst On Thu, Apr 2, 2020, 7:57 PM Steven D'Aprano <steve@pearwood.info> wrote:

On Thu, Apr 02, 2020 at 07:18:47PM +0400, Abdur-Rahmaan Janhangeer wrote:

...

Out of curiosity how did you learn about sys.displayhook?

20+ years of using Python, experimenting at the interpreter, reading the documentation, blog posts, etc. I have no idea *specifically* where I learned it.

I didn't remember the name of the hook, but I knew it existed, so I ran dir(sys) to get a list of objects in the sys module, then tested it to make sure it did what I thought it did.

-- Steven _______________________________________________ Python-ideas mailing list -- python-ideas@python.org To unsubscribe send an email to python-ideas-leave@python.org https://mail.python.org/mailman3/lists/python-ideas.python.org/ Message archived at https://mail.python.org/archives/list/python-ideas@python.org/message/DMKA3C... Code of Conduct: http://python.org/psf/codeofconduct/

On Apr 2, 2020, at 13:35, Abdur-Rahmaan Janhangeer <arj.python@gmail.com> wrote:

...

On Thu, Apr 2, 2020 at 8:15 PM Andrew Barnert <abarnert@yahoo.com> wrote:

Why should modules break all of that, and be different from strings, tuples, functions, classes, etc.?

python-ideas is for ideas without worrying about implementations unless it's about some glaring breaking changes

But nobody’s mentioned implementation here. Nobody’s saying you can’t have this because it would be too hard to implement. (It almost surely wouldn’t be hard. For one thing, there are existing cases of special methods like __dir__, which are normally looked up on the type but for modules they’re looked up on the individual instance, and the same thing presumably could be done here just as easily. Even besides that, most types’ reprs, including module, already include information from the instance, so there’s no reason even without overloading module.__repr__ you couldn’t have a slightly different way to extensively customize the repr of each individual module.) People are saying you probably don’t want this because it would be inconsistent with other reprs, and with what repr is for and how it’s used—e.g., the concise and standard form of reprs is crucial to things like tracebacks and logs being useful for debugging. That’s not about implementation; that’s about the key idea in your proposal.

...

The str, which you get from print(package), might be a different story. If there’s a representation of a module that’s more useful to end users than the repr, even if it’s not as good for debugging, the str should use that representation. But is there? What would the message be? How would the module specify it? And how it would be useful for the end user to see that message? ... I may be misinterpreting something about the goals of your proposal. If so, I apologize—but it would really help if you give a real example: some known module, what message you think it should include in its repr, where you plan to print out that repr, how you’d like to specify it within the module source, etc.

Well as for example from known module, the proposal is all about introducing the __repr__ option in modules. If i understood well it does not seem to exist. As for purpose, well a friendlier representation of a package.

That’s not an example. Show us a module that you’d like to have a custom repr, and show us what you’d like that custom repr to be, and show us that it looks good in other contexts (a traceback, printing out sys.modules, etc.), or why it’s so good in the REPL that it overcomes the cost of being less good in those contexts. You may well have examples that are good enough. But if you don’t show us your examples, we can only use our own imagination, and obviously none of us are imagining anything nearly good enough to be worth it. Which is our failure, not yours—but you want this implemented, and if nobody backs your proposal because nobody imagines how useful it would be, you’re not going to get it.