Weird lambda rebinding/reassignment without me doing it

[A.T.Hofkamp]

Python doesn't use value semantics for variables but reference semantics:

a = [1]
b = a

In many languages, you'd now have 2 lists. In Python you still have one list,
and both a and b refer to it.

Now if you modify the data (the list), both variables will change

a.append(2)  # in-place modification of the list
print b      # will print [1,2]


If you don't want this, you should make a copy somewhere

a = a + [2]

or

b = a[:]


It takes a bit of getting used to, but it is very handy in practice.


Read the docs about 'immutable' and 'mutable' types.
(I expected this to be a FAQ, but I couldn't quickly find a matching entry)


Albert