Question about typing: ints/floats

[Wells]

This seems sort of odd to me:

>>> a = 1
>>> a += 1.202
>>> a
2.202

Indicates that 'a' was an int that was implicitly casted to a float.
But:

>>> a = 1
>>> b = 3
>>> a / b
0

This does not implicitly do the casting, it treats 'a' and 'b' as
integers, and the result as well. Changing 'b' to 3.0 will yield a
float as a result (0.33333333333333331)

Is there some way to explain the consistency here? Does python
implicitly change the casting when you add variables of a different
numeric type?

Anyway, just  curiosity more than anything else. Thanks!