How to Generate Functions Dynamically in Python

Question

Is it possible to generate dynamically class methods which are very similar one another?

Say I have a class like this one:

class KitchenDrawer:

    def _check_if_tool_available(self, tool) -> bool:
        # check if "tool" is in the drawer

    def is_knife_available(self) -> bool:
        return self._check_if_tool_available("knife")

    def is_spoon_available(self) -> bool:
        return self._check_if_tool_available("spoon")

    def is_fork_available(self) -> bool:
        return self._check_if_tool_available("fork")

Is there a way to generate is_knife_available(), is_spoon_available(), is_fork_available() dynamically, so there is not so much repeated code?

(Some of you might suggest to simply make _check_if_tool_available(self, tool) a public facing method and carry on with my life. Fair. But more than the sensible solution, I am interested in the nitty gritty issue here.)

Thanks!

Just use the solution in the last paragraph. Dynamic function creation is possible, but there's 0 reason to use it here (or really, is the vast majority if not all of circumstances). You'd use something like eval to create the functions, but that would just be a hacky way of emulating a parameter. — Carcigenicate
– Carcigenicate, Commented Apr 28, 2024 at 14:24
There a lots of SO questions with answers returned by a simple "python create method dynamically" Google search, what exactly didn't answer your question in them? — Thierry Lathuille
– Thierry Lathuille, Commented Apr 28, 2024 at 14:37
You could override getattr, but that would be a lot of trouble when you could just use a parameter. — CrazyChucky
– CrazyChucky, Commented Apr 28, 2024 at 14:43
It’s possible and not terrible in Python (without eval), but it’s just better practice to not make use of Python’s dynamic features – static analysis (both by tools and humans) is so valuable. I would write out the list of repetitive methods, assuming they’re this simple in reality. — Ry-
– Ry- ♦, Commented Apr 28, 2024 at 14:45

Dmitry Brazhenko · Accepted Answer · 2024-04-28 14:43:47Z

2

Yes, it is possible, but it can be hard-debuggable approach. You can use setattr() for this purposes.

For example, you can implement smth like this:

class KitchenDrawer:
    def _check_tool(self, tool):
        return tool in ['knife', 'spoon', 'fork']

for tool in ['knife', 'spoon', 'fork']:
    setattr(KitchenDrawer, f'is_{tool}_available', lambda self, t=tool: self._check_tool(t))



# Usage
drawer = KitchenDrawer()
print(drawer.is_knife_available())   # True

Also you can check that methods is_fork_available, is_knife_available, is_spoon_available are available in the class:

dir(KitchenDrawer) 
# [... 'is_fork_available', 'is_knife_available', 'is_spoon_available']

Here is a related question that can be helpful with some better approach.

answered Apr 28, 2024 at 14:43

Dmitry Brazhenko

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MoRe · Accepted Answer · 2024-04-28 17:22:28Z

0

class KintchenDrawer:
    def __getattr__(self, attr: str):
        if res := re.findall("is_(\w*?)_available", attr):
            return self._check_if_tool_available(res[0])

Then, you can use self.is_spoon_available without any paranthesis

Do you think it answers your problem? If yes, I can explain it

edited Apr 28, 2024 at 17:22

answered Apr 28, 2024 at 14:51

MoRe

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3 Comments

Dmitry Brazhenko Over a year ago

Definetely a good example!

Joooeey Over a year ago

@DmitryBrazhenko this answer is worse than yours. The methods won't show up in dir(KintchenDrawer) or help(KintchenDrawer) here.

Dmitry Brazhenko Over a year ago

Yes, this will not be show up, but on the other hand, it provides more flexibility.

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