Python Inspect

This is an exploration of the python inspect module. I have come to the conclusion that the yapsy system, while interesting in its own right, is too confusing and big to make sense for the limited things that I want to do with it so this is an attempt to get to know inspect in the hopes that it has enough for me to use.

To start I will use a dummy module and see what I can get from it.

# python standard library
import inspect

# this package
import dummy

The Docstring

The inspect.getdoc gets document strings for objects and formats them.

First the module docstring:

print inspect.getdoc(dummy)

None

Now a class inside the module:

print inspect.getdoc(dummy.DummyClass)

This is a dummy class that inherits from `object`

What about a method for the class?

print inspect.getdoc(dummy.DummyClass.a_tuple)

Puts self.a in a tuple and returns it

:return: (self.a, )

I was actually execting that to fail since I used the class definition instead of an instance, but I guess it works.

Get File

The inspect.getfile method takes an object and tells you the file where it came from:

from dummy import DummyClass
d = DummyClass(a=1)
print inspect.getfile(DummyClass)

try:
    print inspect.getfile(d)
except TypeError as error:
    print error

./dummy.py
<dummy.DummyClass object at 0x3d2ed50> is not a module, class, method, function, traceback, frame, or code object

So, I apparently misunderstood the meaning of the word object, it appears to mean the definition, not an instance of the class I defined.

getargspec

inspect.getargspec should tell you what the arguments are for a method (I think).

print inspect.getargspec(DummyClass.convoluted)

ArgSpec(args=['self', 'a', 'b', 'c', 'd'], varargs=None, keywords=None, defaults=(5, '9', None))

That does not appear to be as useful as I thought it would be.

getmembers

inspect.getmembers returns members of an object, allowing you to pass in a function to filter the particular members you want.

print inspect.getmembers(dummy, inspect.isclass)

[('ABCMeta', <class 'abc.ABCMeta'>), ('AnotherClass', <class 'dummy.AnotherClass'>), ('ConcretePlugin', <class 'dummy.ConcretePlugin'>), ('DummyClass', <class 'dummy.DummyClass'>), ('PluginBase', <class 'dummy.PluginBase'>), ('abstractproperty', <class 'abc.abstractproperty'>)]

I was thinking I could do something like:

print inspect.getmembers(dummy, lambda o: inspect.isclass(o) and o.__name__.startswith('Dummy'))

[('DummyClass', <class 'dummy.DummyClass'>)]

Or maybe (if the classes I want have to be children of the same class):

print inspect.getmembers(dummy, lambda o: inspect.isclass(o) and o.__base__ is DummyClass)

[('AnotherClass', <class 'dummy.AnotherClass'>)]

I had thought that I would be matching the name of the base-class but __base__ returns a type object.

Discovering Modules

One of the things that maybe can be done is import modules on the fly. Here I will look for:

ConcretePlugin

import os
import importlib

from dummy import PluginBase

for filename in os.listdir(os.getcwd()):
    # the print statements in this module are showing up in the output when I import it
    if filename.endswith('.py') and not filename=='explore_inspect.py':
        base, extension = os.path.splitext(filename)
        try:
            candidate = importlib.import_module(base)
        except ImportError as error:
            # for some reason nose is using /usr/lib/python2.7/importlib
            # and this is causing it to fail
            print error
            continue
        members = inspect.getmembers(candidate, lambda o: inspect.isclass(o) and o.__base__ is PluginBase)
        for member in members:
            name, definition = member
            print name
            m = definition()
            print 'Help:'
            print m.help_string
            print "Config:"
            print m.config
            print "Product:"
            print m.product

.. toctree::
   :maxdepth: 2

   Python Inspect <explore_inspect.rst>
   The Dummy Module <dummy.rst>

.. toctree::
   :maxdepth: 2


ConcretePlugin
Help:

        Now is the winter of our disconcent.

Config:

        [CONCRETE]
        zero = 0

Product:
0

Presumably in the real code there would be some variation of __package__ in there instead of current-working-directory, but in Pweave it returns None for some reason.