I ran into this question in an interview and couldn't come up with a solution. I know the vice versa can be done as shown in What does the "+=" operator do in Java?

So the question was like below.

..... x = .....;
..... y = .....;

x += y; //compile error
x = x + y; //works properly

Try this code

Object x = 1;
String y = "";

x += y; //compile error
x = x + y; //works properly

not entirely sure why this works, but the compiler says

The operator += is undefined for the argument type(s) Object, String

and I assume that for the second line, toString is called on the Object.

EDIT:

It makes sense as the += operator is meaningless on a general Object. In my example I cast an int to an Object, but it only depends on x being of type Object:

Object x = new Object();

It only works if x is Object though, so I actually think it is more that String is a direct subclass of Object. This will fail for x + y:

Foo x = new Foo();

for other types that I have tried.

Why does 4 < '3' return True in Python 2?

Is it because when I place single quotes around a number Python sees it as a string and strings are bigger than numbers?

Yes, any number will be less than any string (including the empty string) in Python 2.

In Python 3, you can't make arbitrary comparisons. You'll get a TypeError.

---

From the link in eryksun's comment:

if (PyNumber_Check(v))
    vname = "";
else
    vname = v->ob_type->tp_name;
if (PyNumber_Check(w))
    wname = "";
else
    wname = w->ob_type->tp_name;
c = strcmp(vname, wname);

So at least in recent versions of CPython 2.x, type names are compared, with an empty string used instead of the type name for any numeric type.