How to validate the __init__ parameters

[Denis Doria]

Hi;

I'm checking the best way to validate attributes inside a class. Of
course I can use property to check it, but I really want to do it
inside the __init__:

class A:
    def __init__(self, foo, bar):
        self.foo = foo #check if foo is correct
        self.bar = bar

All examples that I saw with property didn't show a way to do it in
the __init__. Just to clarify, I don't want to check if the parameter
is an int, or something like that, I want to know if the parameter do
not use more than X chars; and want to do it when I'm 'creating' the
instance; not after the creation:

a = A('foo', 'bar')

not

class A:
    def __init__(self, foo = None, bar = None):
        self._foo = foo
        self._bar = bar
    def  set_foo(self, foo):
        if len(foo) > 5:
             raise <something>
        _foo = foo
    foo = property(setter = set_foo)

a = A()
a.foo = 'foo'


I thought in something like:

class A:
    def __init__(self, foo = None, bar = None):
        set_foo(foo)
        self._bar = bar
    def  set_foo(self, foo):
        if len(foo) > 5:
             raise <something>
        _foo = foo
    foo = property(setter = set_foo)

But looks too much like java