__getattr__ on a module

This is a hack, but you can wrap the module with a class:

class Wrapper(object):
  def __init__(self, wrapped):
    self.wrapped = wrapped
  def __getattr__(self, name):
    # Perform custom logic here
    try:
      return getattr(self.wrapped, name)
    except AttributeError:
      return 'default' # Some sensible default

sys.modules[__name__] = Wrapper(sys.modules[__name__])

We don’t usually do it that way.

What we do is this.

class A(object):
....

# The implicit global instance
a= A()

def salutation( *arg, **kw ):
    a.salutation( *arg, **kw )

Why? So that the implicit global instance is visible.

For examples, look at the random module, which creates an implicit global instance to slightly simplify the use cases where you want a “simple” random number generator.

Similar to what @Håvard S proposed, in a case where I needed to implement some magic on a module (like __getattr__), I would define a new class that inherits from types.ModuleType and put that in sys.modules (probably replacing the module where my custom ModuleType was defined).

See the main __init__.py file of Werkzeug for a fairly robust implementation of this.

Create your module file that has your classes. Import the module. Run getattr on the module you just imported. You can do a dynamic import using __import__ and pull the module from sys.modules.

Here’s your module some_module.py:

class Foo(object):
    pass

class Bar(object):
    pass

And in another module:

import some_module

Foo = getattr(some_module, 'Foo')

Doing this dynamically:

import sys

__import__('some_module')
mod = sys.modules['some_module']
Foo = getattr(mod, 'Foo')

This is hackish, but…

# Python 2.7
import types


class A(object):
    def salutation(self, accusative):
        print("hello", accusative)
    def farewell(self, greeting, accusative):
         print(greeting, accusative)


def AddGlobalAttribute(classname, methodname):
    print("Adding " + classname + "." + methodname + "()")
    def genericFunction(*args):
        return globals()[classname]().__getattribute__(methodname)(*args)
    globals()[methodname] = genericFunction


# set up the global namespace
x = 0   # X and Y are here to add them implicitly to globals, so
y = 0   # globals does not change as we iterate over it.


toAdd = []


def isCallableMethod(classname, methodname):
    someclass = globals()[classname]()
    something = someclass.__getattribute__(methodname)
    return callable(something)


for x in globals():
    print("Looking at", x)
    if isinstance(globals()[x], (types.ClassType, type)):
        print("Found Class:", x)
        for y in dir(globals()[x]):
            if y.find("__") == -1: # hack to ignore default methods
                if isCallableMethod(x,y):
                    if y not in globals(): # don't override existing global names
                        toAdd.append((x,y))
    # Returns:
    # ('Looking at', 'A')
    # ('Found Class:', 'A')
    # ('Looking at', 'toAdd')
    # ('Looking at', '__builtins__')
    # ('Looking at', 'AddGlobalAttribute')
    # ('Looking at', 'register')
    # ('Looking at', '__package__')
    # ('Looking at', 'salutation')
    # ('Looking at', 'farewell')
    # ('Looking at', 'types')
    # ('Looking at', 'x')
    # ('Looking at', 'y')
    # ('Looking at', '__name__')
    # ('Looking at', 'isCallableMethod')
    # ('Looking at', '__doc__')
    # ('Looking at', 'codecs')



for x in toAdd:
    AddGlobalAttribute(*x)


if __name__ == "__main__":
    salutation("world")
    farewell("goodbye", "world")


# Returns:
# hello world
# goodbye world

This works by iterating over the all the objects in the global namespace. If the item is a class, it iterates over the class attributes. If the attribute is callable it adds it to the global namespace as a function.

It ignore all attributes which contain "__".

I wouldn’t use this in production code, but it should get you started.

There are two basic problems you are running into here:

1. __xxx__ methods are only looked up on the class
2. TypeError: can't set attributes of built-in/extension type 'module'

(1) means any solution would have to also keep track of which module was being examined, otherwise every module would then have the instance-substitution behavior; and (2) means that (1) isn’t even possible… at least not directly.

Fortunately, sys.modules is not picky about what goes there so a wrapper will work, but only for module access (i.e. import somemodule; somemodule.salutation('world'); for same-module access you pretty much have to yank the methods from the substitution class and add them to globals() eiher with a custom method on the class (I like using .export()) or with a generic function (such as those already listed as answers). One thing to keep in mind: if the wrapper is creating a new instance each time, and the globals solution is not, you end up with subtly different behavior. Oh, and you don’t get to use both at the same time — it’s one or the other.

---

Update

From Guido van Rossum:

There is actually a hack that is occasionally used and recommended: a
module can define a class with the desired functionality, and then at
the end, replace itself in sys.modules with an instance of that class
(or with the class, if you insist, but that’s generally less useful).
E.g.:

# module foo.py

import sys

class Foo:
    def funct1(self, <args>): <code>
    def funct2(self, <args>): <code>

sys.modules[__name__] = Foo()

This works because the import machinery is actively enabling this
hack, and as its final step pulls the actual module out of
sys.modules, after loading it. (This is no accident. The hack was
proposed long ago and we decided we liked enough to support it in the
import machinery.)

So the established way to accomplish what you want is to create a single class in your module, and as the last act of the module replace sys.modules[__name__] with an instance of your class — and now you can play with __getattr__/__setattr__/__getattribute__ as needed.

---

Note 1: If you use this functionality then anything else in the module, such as globals, other functions, etc., will be lost when the sys.modules assignment is made — so make sure everything needed is inside the replacement class.

Note 2: To support from module import * you must have __all__ defined in the class; for example:

class Foo:
    def funct1(self, <args>): <code>
    def funct2(self, <args>): <code>
    __all__ = list(set(vars().keys()) - {'__module__', '__qualname__'})

Depending on your Python version, there may be other names to omit from __all__. The set() can be omitted if Python 2 compatibility is not needed.

Here’s my own humble contribution — a slight embellishment of @Håvard S’s highly rated answer, but a bit more explicit (so it might be acceptable to @S.Lott, even though probably not good enough for the OP):

import sys

class A(object):
    def salutation(self, accusative):
        print "hello", accusative

class Wrapper(object):
    def __init__(self, wrapped):
        self.wrapped = wrapped

    def __getattr__(self, name):
        try:
            return getattr(self.wrapped, name)
        except AttributeError:
            return getattr(A(), name)

_globals = sys.modules[__name__] = Wrapper(sys.modules[__name__])

if __name__ == "__main__":
    _globals.salutation("world")