Why in python list += [elem] modifies the original list?
    >>> list1 = []
    >>> list2 = list1
    >>> list2 += [1]
    >>> print list1
    [1]

Comparing this to

    >>> list1 = []
    >>> list2 = list1
    >>> list2 = list2 + [1]
    >>> print list1
    []

Is there a reason why the '+='-operation modifies the original list?

Why in python list += [elem] modifies the original list?
===

    >>> list1 = []
    >>> list2 = list1
    >>> list2 += [1]
    >>> print list1
    [1]

Comparing this to

    >>> list1 = []
    >>> list2 = list1
    >>> list2 = list2 + [1]
    >>> print list1
    []

Is there a reason why the '+='-operation modifies the original list?
