[issue21561] help() on enum34 enumeration class creates only a dummy documentation

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

Python 2.7 is no longer supported.

--
nosy: +serhiy.storchaka
resolution:  -> out of date
stage: test needed -> resolved
status: open -> closed

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[issue21561] help() on enum34 enumeration class creates only a dummy documentation

[Andy Maier]

Andy Maier added the comment:

Attaching the patch for pydoc.py, relative to the tip of 2.7. the patch 
contains just the proposed fix, and no longer the debug prints.

--
keywords: +patch
Added file: http://bugs.python.org/file35673/pydoc.py.patch

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[issue21561] help() on enum34 enumeration class creates only a dummy documentation

[Andy Maier]

Andy Maier added the comment:

Attaching the patch for Lib/test/test_pydoc.py, relative to the tip of 2.7. The 
patch adds a testcase test_class_with_metaclass(), which defines a class that 
provokes the buggy behavior, and verifies the fix.

--
Added file: http://bugs.python.org/file35674/test_pydoc.py.patch

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[issue21561] help() on enum34 enumeration class creates only a dummy documentation

[Andy Maier]

Andy Maier added the comment:

Using Ethan's sample code (Thanks!!), I was pointed in the right direction and 
was able to produce a simple piece of code that reproduces the behavior without 
depending on enum34, as well as a proposal for a fix in pydoc.py.

The problem can be reproduced with a class that specifies a metaclass that has 
class attributes and includes these class attributes in its __dir__() result, 
which causes them to propagate as class attributes to the class using that 
metaclass, at least for the purposes of pydoc.

In the course of the processing within pydoc.py, the tuple returned by 
inspect.classify_class_attrs() for such class attributes then has None for its 
class item, which triggers the issue I originally reported (pydoc traps and 
produces just a dummy help description).

In my original problem with the enum34 module, the same thing happens, just 
here the propagated class attributes include the __members__ list, which is 
defined as a property. So I do believe that my simple code represents the same 
error situation as the original enum34 issue.

Because pydoc.py already has its own classify_class_attrs() function that 
wrappers inspect.classify_class_attrs() for the purpose of treating data 
descriptors correctly, I think it would be acceptable to continue down the path 
of fixing it up, just this case for class attributes propagated by the 
metaclass. That's what my proposed fix does.

Unfortunately, it seems one can attach only one file, so I paste the 
reproduction code in here, and attach the fixed pydoc.py.

Here is the code that reproduces the issue:
 bug2.py
# Boolean test switches that control whether a class variable of the metaclass
# is added to the dir() result.
# If the fix is not present, then enabling each one triggers the error
# behavior; If none of them is enabled, the error behavior is not triggered.
with_food = True  # Add the 'normal' class attribute 'food'
with_drink = True # Add the property-based class attribute 'drink'

class FoodMeta(type):
Metaclass that adds its class attributes to dir() of classes using it.

food = 'ham'  # 'normal' class attribute

@property
def drink(cls):   # property-based class attribute
return 'beer'

def __dir__(cls):
ret = [name for name in cls.__dict__] # the normal list
if with_food:
ret += ['food']
if with_drink:
ret += ['drink']
print bug2.FoodMeta.__dir__(): return=%s % (repr(ret),)
return ret

class Food(object):
docstring for Food class
__metaclass__ = FoodMeta

def diet(self):
return no!

if __name__ == '__main__':
print bug2: Calling help(Food):
help(Food)



- Please review the reproduction code and the fix and let me know how to 
proceed.

Andy

--
Added file: http://bugs.python.org/file35501/pydoc_fix2.py

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[issue21561] help() on enum34 enumeration class creates only a dummy documentation

[Andy Maier]

Andy Maier added the comment:

Here is the bug2.py file pasted into the previous message, for convenience.

--
Added file: http://bugs.python.org/file35502/bug2.py

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[issue21561] help() on enum34 enumeration class creates only a dummy documentation

[Ethan Furman]

Ethan Furman added the comment:

I think something like the following, taken from 
http://bugs.python.org/issue19030#msg199920, shoud do the trick for something 
to test against:

class Meta(type):
def __getattr__(self, name):
if name == 'ham':
return 'spam'
return super().__getattr__(name)

class VA(metaclass=Meta):
@types.DynamicClassAttribute
def ham(self):
return 'eggs'

which should result in:

VA_instance = VA()
VA_instance.ham  # should be 'eggs'
VA.ham   # should be 'spam'

Combining all that with the DynamicClassAttribute should make a fitting test.  
Thanks, Andreas, for working on that.

--
assignee:  - ethan.furman

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[issue21561] help() on enum34 enumeration class creates only a dummy documentation

[Ned Deily]

Changes by Ned Deily n...@acm.org:


--
nosy:  -ned.deily

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[issue21561] help() on enum34 enumeration class creates only a dummy documentation

[Terry J. Reedy]

Terry J. Reedy added the comment:

Devise a simple test (fail before, work after) that does not require enum34. If 
this fix is committed, the message could note that the same issue was fixed 
differently in 3.4 mixed in with other changes.

--
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stage:  - test needed

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[issue21561] help() on enum34 enumeration class creates only a dummy documentation

[Andy Maier]

Andy Maier added the comment:

The pydoc.py of Python 3.4 that supposedly has been fixed has a lot of changes 
compared to 2.7, but the place where I applied my fix in TextDoc.docclass() 
is unchanged.

So it seems that my fix should be regarded only to be a quick fix, and the real 
fix would be somewhere in the 3.4 pydoc.py. I tried to understand the changes 
but gave up after a while. My quick fix (with a better text than one that 
contains TBD) is still better than not having it fixed, but more ideally the 
real fix should be rolled back to the 2.7 pydoc.py.

Is there anything else I can do to help with this bug?

--

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[issue21561] help() on enum34 enumeration class creates only a dummy documentation

[Andy Maier]

New submission from Andy Maier:

Using the enum34 backport of enums, the help() function on an enum class Colors 
displays only:


---
Help on class Colors in module __main__:

Colors = enum 'Colors'
---

Source code to reproduce:
---
from enum import Enum # enum34 package

class Colors(Enum):
docstring for enumeration Colors
RED = 1
GREEN = 2
BLUE = [3]

help(Colors)
---

Versions used:
  python 2.7.6
  enum34 1.0
Platform: Windows 7

I debugged the issue, found the place where it breaks down, and made a fix. 
However, it may well be that the fix is just a cure to a symptom, and that a 
better fix is possible.

Here is the fix:
In pydoc.py, class TextDoc, method docclass():
Change this code on line 1220+:
---
if thisclass is __builtin__.object:
attrs = inherited
continue
elif thisclass is object:
tag = defined here
else:
tag = inherited from %s % classname(thisclass,
  object.__module__)
---
to this, by adding the two lines marked with added:
---
if thisclass is __builtin__.object:
attrs = inherited
continue
elif thisclass is object:
tag = defined here
elif thisclass is None:# -- added
tag = inherited from TBD # -- added
else:
tag = inherited from %s % classname(thisclass,
  object.__module__)
---

It breaks down during the last round through the 'while attrs' loop, where 
thisclass is None. I did not investigate why thisclass is None.

Without the fix, this causes an AttributeError to be raised by the classname() 
function, which then further on causes the dummy documentation to be generated.

With the fix, the help(Colors) output becomes:

---
Help on class Colors in module __main__:

class Colors(enum.Enum)
 |  docstring for enumeration Colors
 |
 |  Method resolution order:
 |  Colors
 |  enum.Enum
 |  __builtin__.object
 |
 |  Data and other attributes defined here:
 |
 |  BLUE = Colors.BLUE: [3]
 |
 |  GREEN = Colors.GREEN: '2'
 |
 |  RED = Colors.RED: 1
 |
 |  --
 |  Data and other attributes inherited from TBD:
 |
 |  __members__ = {'BLUE': Colors.BLUE: [3], 'GREEN': Colors.GREEN: '2'...
---

--
components: Library (Lib)
files: bug1.py
messages: 218979
nosy: andymaier
priority: normal
severity: normal
status: open
title: help() on enum34 enumeration class creates only a dummy documentation
type: behavior
versions: Python 2.7
Added file: http://bugs.python.org/file35327/bug1.py

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[issue21561] help() on enum34 enumeration class creates only a dummy documentation

[Ethan Furman]

Ethan Furman added the comment:

Good work.

This bug was fixed in 3.4 with the inclusion of enum.

It would definitely be good to fix in 2.7 as well.

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[issue21561] help() on enum34 enumeration class creates only a dummy documentation

[Ned Deily]

Ned Deily added the comment:

If the problem reported here applies only to the 2.7 backport of enum, which is 
not part of the Python standard library, shouldn't this issue be closed?

--
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[issue21561] help() on enum34 enumeration class creates only a dummy documentation

[Ethan Furman]

Ethan Furman added the comment:

The problem will affect anything that uses the same mechanism as enum.  It also 
affects (not verified) all versions of python up to 3.4 where it was fixed 
because enum exposed it.

Besides which, I did not think a bug had to affect stdlib code in order to be 
fixed -- or this just a 2.7 restriction since it's basically end-of-lifed?

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[issue21561] help() on enum34 enumeration class creates only a dummy documentation

[Ned Deily]

Ned Deily added the comment:

Sorry, I skimmed over the issue and didn't notice that the fix applied to 
pydoc.py, not enum.

--

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