[issue30129] functools.partialmethod should look more like what it's impersonating.

[Sylvain Marie]

Sylvain Marie  added the comment:

For future reference if this topic re-opens, there is now an alternative here:

https://smarie.github.io/python-makefun/#removing-parameters-easily

Note: it relies on a dynamic `compile` statement so of course it is less 
optimal than the one in functools. But at least it can serve as a reference...

--
nosy: +smarie

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue30129] functools.partialmethod should look more like what it's impersonating.

[Karthikeyan Singaravelan]

Karthikeyan Singaravelan  added the comment:

I did some analysis with the given example script. Related issue where Aaron 
has some analysis : issue12154 . The patch doesn't break anything since there 
are no tests for this that also could be added.

1. When we do inspect.getdoc(c.sum) it looks for obj.__doc__ (c.sum.__doc__) 
returning partialmethod.__doc__ ("new function with partial...") instead of 
checking if c.sum is a partial method and  returning obj.func.__doc__ which 
contains the relevant doc ("sum doc"). Thus getdoc needs to check before trying 
for obj.__doc__ if the obj is a partialmethod or partial object thus returning 
the original function object.

2. When we do inspect.getdoc(Child.sum) it looks for obj.__doc__ 
(Child.sum.__doc__) and since Child.sum is a partialmethod which has __get__ 
overridden it calls _make_unbound_method that returns a _method object with no 
doc and thus returning None. partialmethod object copies objects from the given 
function at 
https://github.com/python/cpython/blob/f1b9ad3d38c11676b45edcbf2369239bae436e56/Lib/functools.py#L368
 and the actual object is returned at 
https://github.com/python/cpython/blob/f1b9ad3d38c11676b45edcbf2369239bae436e56/Lib/functools.py#L401
 . Here self.func has the original function in this case Base.sum and 
_method._partialmethod has reference to Base.sum which contains the relevant 
docs but _method itself has no docs thus pydoc doesn't get any docs. So we can 
set _method.__doc__ = self.func.__doc__ and getdoc can pick up the docs.

sample script with

print(pydoc.render_doc(Child))
print(pydoc.render_doc(c))
print(inspect.getdoc(c.sum)) # Need to patch getdoc before it checks for 
obj.__doc__ to check if the c.sum is an instance of partialmethod or partial
print(inspect.getdoc(Child.sum)) # Need to patch 
functools.partialmethod._make_unbound_method to copy the docs to _method

Output :

```
Python Library Documentation: class Child in module __main__

class Child(builtins.object)
 |  Methods defined here:
 |
 |  diff(self, arg1, arg2)
 |  diff doc
 |
 |  sum = _method(self, arg2)
 |  sum doc
 |
 |  --
 |  Data descriptors defined here:
 |
 |  __dict__
 |  dictionary for instance variables (if defined)
 |
 |  __weakref__
 |  list of weak references to the object (if defined)

Python Library Documentation: Child in module __main__ object

class Child(builtins.object)
 |  Methods defined here:
 |
 |  diff(self, arg1, arg2)
 |  diff doc
 |
 |  sum = _method(self, arg2)
 |  sum doc
 |
 |  --
 |  Data descriptors defined here:
 |
 |  __dict__
 |  dictionary for instance variables (if defined)
 |
 |  __weakref__
 |  list of weak references to the object (if defined)

sum doc
sum doc

```

patch : 

diff --git a/Lib/functools.py b/Lib/functools.py
index ab7d71e126..751f67fcd0 100644
--- a/Lib/functools.py
+++ b/Lib/functools.py
@@ -398,6 +398,7 @@ class partialmethod(object):
 return self.func(*call_args, **call_keywords)
 _method.__isabstractmethod__ = self.__isabstractmethod__
 _method._partialmethod = self
+_method.__doc__ = self.func.__doc__ or self.__doc__
 return _method

 def __get__(self, obj, cls):
diff --git a/Lib/inspect.py b/Lib/inspect.py
index b8a142232b..2c796546b2 100644
--- a/Lib/inspect.py
+++ b/Lib/inspect.py
@@ -600,6 +600,9 @@ def getdoc(object):
 All tabs are expanded to spaces.  To clean up docstrings that are
 indented to line up with blocks of code, any whitespace than can be
 uniformly removed from the second line onwards is removed."""
+if isinstance(object, (functools.partialmethod, functools.partial)):
+return object.func.__doc__
+
 try:
 doc = object.__doc__
 except AttributeError:

--
nosy: +xtreak

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue30129] functools.partialmethod should look more like what it's impersonating.

[Aaron Hall]

Change by Aaron Hall :


--
nosy: +Aaron Hall

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue30129] functools.partialmethod should look more like what it's impersonating.

[Skip Montanaro]

Skip Montanaro added the comment:

Again, my apologies for the crappy initial bug report. Hopefully this comment 
and the two files I just attached demonstrate what I am getting at.

I just uploaded a stupid little example, partial3.py. Stupid, but still, it 
demonstrates part of how I think docstrings on these partial methods could be 
improved. If you run it (I'm using Python 3.6.1), note that the doc strings for 
the sum method (instance and class), look wrong:

Child.sum doc: None
c.sum doc: partial(func, *args, **keywords) - new function with partial 
application
of the given arguments and keywords.

The file, ft.diff, includes a one-line patch to partialmethod.__get__ which 
corrects the docstring for the instance of the Child class:

Child.sum doc: None
c.sum doc: sum doc

I haven't looked to see where the docstring of Child.sum could be set, but I 
believe it should be fairly straightforward for someone more familiar with this 
code. Also, the patch doesn't improve the output of pydoc:

partial3.Child = class Child(builtins.object)
 |  Methods defined here:
 |  
 |  diff(self, arg1, arg2)
 |  diff doc
 |  
 |  sum = _method(self, arg2)
 |  
 |  --
 |  Data descriptors defined here:
 |  
 |  __dict__
 |  dictionary for instance variables (if defined)
 |  
 |  __weakref__
 |  list of weak references to the object (if defined)

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue30129] functools.partialmethod should look more like what it's impersonating.

[Skip Montanaro]

Changes by Skip Montanaro :


--
keywords: +patch
Added file: http://bugs.python.org/file46824/ft.diff

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue30129] functools.partialmethod should look more like what it's impersonating.

[Skip Montanaro]

Changes by Skip Montanaro :


Added file: http://bugs.python.org/file46823/partial3.py

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue30129] functools.partialmethod should look more like what it's impersonating.

[Skip Montanaro]

Skip Montanaro added the comment:

Yeah, sorry about that. I work in an environment where I can't "eject" any
code from my work computer. I've come up with a simple Python3 example, but
it will have to wait until I can recreate it from scratch on my home
computer.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue30129] functools.partialmethod should look more like what it's impersonating.

[R. David Murray]

R. David Murray added the comment:

Yes, please do provide an example. Your final words do not make a convincing 
case that this is a problem in python3 :)

--
nosy: +r.david.murray

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue30129] functools.partialmethod should look more like what it's impersonating.

[Skip Montanaro]

New submission from Skip Montanaro:

I needed to create a partial method in Python 2.7, so I grabbed 
functools.partialmethod from a Python 3.5.2 install. For various reasons, one 
of the reasons I wanted this was to suck in some methods from a delegated class 
so they appeared in dir() and help() output on the primary class (the one 
containing the partialmethod objects). Suppose I have

class Something:
  def meth(self, arg1, arg2):
"meth doc"
return arg1 + arg2

then in the metaclass for another class I construct an attribute (call it 
"mymeth") which is a partialmethod object. When I (for example), run pydoc, 
that other class's attribute appears as:

mymeth = 

It would be nice if it at least included the doc string from meth, something 
like:

mymeth = 
meth doc

Even better would be a proper signature:

mymeth(self, arg1, arg2)
meth doc

In my copy of functools.partialmethod, I inserted an extra line in __get__, 
right after the call to partial():

results.__doc__ = self.func.__doc__

That helps a bit, as I can

print("mymeth doc:", inst.mymeth.__doc__)

and see

mymeth doc: meth doc

displayed. That's not enough for help()/pydoc though.

I suspect the heavy lifting will have to be done in pydoc.Doc.document(). 
inspect.isroutine() returns False for functools.partial objects. I also see 
_signature_get_partial() in inspect.py. That might be the source of the 
problem. When I create a partialmethod object in my little example, it actually 
looks like a functools.partial object, not a partialmethod object. It's not 
clear that this test:

if isinstance(partialmethod, functools.partialmethod):

in inspect._signature_from_callable() is testing for the correct type.

Apologies that I can't easily provide a detailed example. My Python 2.x 
metaclass example (where I'm smashing methods from one class into another) 
doesn't work in Python 3.x for some reason, the whole partialmethod thing isn't 
available in Python 2.x (inspect doesn't know about partialmethod or partial) 
and it's not really a "hello world"-sized example anyway. I'll beat on things a 
bit more to try and craft a workable Python 3.x example.

--
components: Library (Lib)
messages: 292050
nosy: skip.montanaro
priority: normal
severity: normal
status: open
title: functools.partialmethod should look more like what it's impersonating.
type: enhancement
versions: Python 3.7

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com