Helper function injected on all python objects?

Question

I'm trying to mimic methods.grep from Ruby which simply returns a list of available methods for any object (class or instance) called upon, filtered by regexp pattern passed to grep. Very handy for investigating objects in an interactive prompt.

def methods_grep(self, pattern):
    """ returns list of object's method by a regexp pattern """
    from re import search
    return [meth_name for meth_name in dir(self) \
            if search(pattern, meth_name)]

Because of Python's limitation not quite clear to me it unfortunately can't be simply inserted in the object class ancestor:

object.mgrep = classmethod(methods_grep)
# TypeError: can't set attributes of built-in/extension type 'object'

Is there some workaround how to inject all classes or do I have to stick with a global function like dir ?

You can list all the methods an object has using dir(), e.g. dir(some_object) (edit: ok I see you already know that ;) — James
– James, Commented Jun 11, 2014 at 13:02
@James I'm aware of that, it's used in the example methods_grep function. I need a function available on all objects which returns all available methods filtered by the pattern given as argument. — David Unric
– David Unric, Commented Jun 11, 2014 at 13:05
@James For example str.mgrep('split') would return ['_formatter_field_name_split', 'rsplit', 'split', 'splitlines']. — David Unric
– David Unric, Commented Jun 11, 2014 at 13:06
You might fake it using the mock module, although it might be dicey setting up a Mock that delegates every thing to the original object type in addition to handling the mgrep method as well. — chepner
– chepner, Commented Jun 11, 2014 at 13:17

user3419537 · Accepted Answer · 2014-06-11 14:37:36Z

4

There is a module called forbiddenfruit that enables you to patch built-in objects. It also allows you to reverse the changes. You can find it here https://pypi.python.org/pypi/forbiddenfruit/0.1.1

from forbiddenfruit import curse    
curse(object, "methods_grep", classmethod(methods_grep))

Of course, using this in production code is likely a bad idea.

edited Jun 11, 2014 at 14:37

answered Jun 11, 2014 at 14:17

user3419537

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3 Comments

David Unric Over a year ago

Thanks, it looks interesting. What's wrong with that module in production use ? Performance issues ?

freakish Over a year ago

Note that this is not a pure Python module. It's a C plugin to Python. This at least makes it less compatible with different Python versions. +1 though since it answers the question.

user3419537 Over a year ago

@David I was referring to the general practice of modifying built-in types. For your stated purpose it is probably harmless.

freakish · Accepted Answer · 2014-06-11 13:50:03Z

2

There is no workaround AFAIK. I find it quite annoying that you can't alter built-in classes. Personal opinion though.

One way would be to create a base object and force all your objects to inherit from it.

But I don't see the problem to be honest. You can simply use methods_grep(object, pattern), right? You don't have to insert it anywhere.

edited Jun 11, 2014 at 13:50

answered Jun 11, 2014 at 13:41

freakish

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2 Comments

wheaties Over a year ago

This is both safer and less error prone to other people using your library.

David Unric Over a year ago

Thanks. I've presumed I'd need to stick with this and leave it as a global function.

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