how do i create object-instances on runtime in python?
say i have 2 classes:
class MyClassA(object):
def __init__(self, prop):
self.prop = prop
self.name = "CLASS A"
def println(self):
print self.name
class MyClassB(object):
def __init__(self, prop):
self.prop = prop
self.name = "CLASS B"
def println(self):
print self.name
and a dict
{('a': MyClassA), ('b': MyClassB)}
how can i create dynamic an instance of one of my two classes, depending of i choose 'a' or 'b'.
kind of this:
somefunc(str):
if 'a': return new MyClassA
if 'b': return new MyClassB
to get "CLASS B" on calling: somefunc('a').println
but in a more elegant and dynamic way (say i add more classes to the dict on runtime)
You might create a dispatcher, which is a dictionary with your keys mapping to classes.
dispatch = {
"a": MyClassA,
"b": MyClassB,
}
instance = dispatch[which_one]() # Notice the second pair of parens here!
You create a class instance by calling the class. Your class dict {('a': MyClassA), ('b': MyClassB)}
returns classes; so you need only call the class:
classes['a']()
But I get the sense you want something more specific. Here's a subclass of dict
that, when called with a key, looks up the associated item and calls it:
>>> class ClassMap(dict):
... def __call__(self, key, *args, **kwargs):
... return self.__getitem__(key)(*args, **kwargs)
...
>>> c = ClassMap()
>>> c['a'] = A
>>> c['b'] = B
>>> c('a')
<__main__.A object at 0x1004cc7d0>
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