Instantiating objects in python

Question

I have a python class I want to instantiate and the __init__ definition has a lot of parameters (10+). Is there a clean way to instantiate a class who's __init__ takes a lot of params?

For example:

class A(object):

    def __init__(self, param1, param2, param3,...param13):
    // create an instance of A


my_a = new A(param1="foo", param2="bar", param3="hello"....)

Is there a cleaner way to do this? like passing in a dictionary or something? Or better, is there an expected convention?

Answer 1

Yes, you can use a dict to collect the parameters:

class A(object):
    def __init__(self, param1, param2, param3):
        print param1, param2, param3


params = {'param1': "foo", 'param2': "bar", 'param3': "hello"}
# no 'new' here, just call the class
my_a = A(**params)

See the unpacking argument lists section of the Python tutorial.

Also, // isn't a comment in Python, it's floor division. # is a comment. For multi-line comments, '''You can use triple single quotes''' or """triple double quotes""".

Answer 2

There is no new keyword in Python. You just invoke the class name as you would a function.

You may specify keyword arguments using a dictionary by prefixing the dictionary with **, for example:

options = {
    "param1": "foo",
    "param2": "bar",
    "param3": "baz"
}

my_a = A(**options)

If you're going to be defining all of the values at once, using a dictionary doesn't really give you any advantage over just specifying them directly while using extra whitespace for clairity:

my_a = A(
    param1 = "foo",
    param2 = "bar",
    param3 = "baz"
)