CODEWITHSUNDEEP
python
Allen Wang
Allen Wang

Reputation: 2502

building a python function from an arbitrarily long list of parameters

I am trying to construct a python lambda function from either a single parameter or a list, and am unsure what syntax to use to build the lambda:

def check_classes_filter(*class):
    return lambda x: isinstance(x, class) and isinstance(x, class[1]...)

The lambda should check if x is an instance of any number of classes that is passed to the function (either one or many).

Is there a general way to build functions from an arbitrary number of parameters in python, maybe as a kind of comprehension?

Upvotes: 1

Views: 75

Answers (2)

Eric Duminil
Eric Duminil

Reputation: 54223

If you want to check that an object is an instance of any listed class, you don't need to define anything:

>>> isinstance('test', int)
False
>>> isinstance('test', str)
True
>>> isinstance('test', (int, str))
True

From isinstance documentation :

If classinfo is a tuple of type objects (or recursively, other such tuples), return true if object is an instance of any of the types.

In your question, you mention if x is an instance of any number of classes that is passed to the function (either one or many), it would mean that you should or instead of and in your boolean logic. If you want to check that an object is an instance of every listed classes, see the answer with all.

Upvotes: 2

Cory Kramer
Cory Kramer

Reputation: 117856

You could loop over your classes args using all.

def check_classes_filter(*classes):
    return lambda x: all(isinstance(x, c) for c in classes)

>>> fun = check_classes_filter(str)
>>> fun('hello')
True
>>> fun = check_classes_filter(int, str)
>>> fun('hello')
False

Although I'd prefer just passing in a list of classes

def check_classes_filter(classes):
    return lambda x: all(isinstance(x, c) for c in classes)

and calling the function as

check_classes_filter([int, str])

Upvotes: 3

Related Questions