The same variable through a list comprehension.

python_magic.same_variable.00.py

def foo():
    x0 = [[1, 2], [3, 4], [5, 6]]
    y = [x2 for x1 in x0 for x2 in x1]
    print y

def bar():
    x = [[1, 2], [3, 4], [5, 6]]
    x = [x for x in x for x in x]
    print x

python_magic.same_variable.00i.py

>>> def foo():
...     x0 = [[1, 2], [3, 4], [5, 6]]
...     y = [x2 for x1 in x0 for x2 in x1]
...     print y
...
>>> def bar():
...     x = [[1, 2], [3, 4], [5, 6]]
...     x = [x for x in x for x in x]
...     print x
...
>>> foo()
[1, 2, 3, 4, 5, 6]
>>> bar()
[1, 2, 3, 4, 5, 6]
>>>

python_magic.same_variable.01i.py

>>> import dis
>>> dis.dis(foo.__code__)
  2           0 LOAD_CONST               1 (1)
              3 LOAD_CONST               2 (2)
              6 BUILD_LIST               2
              9 LOAD_CONST               3 (3)
             12 LOAD_CONST               4 (4)
             15 BUILD_LIST               2
             18 LOAD_CONST               5 (5)
             21 LOAD_CONST               6 (6)
             24 BUILD_LIST               2
             27 BUILD_LIST               3
             30 STORE_FAST               0 (x0)

  3          33 BUILD_LIST               0
             36 LOAD_FAST                0 (x0)
             39 GET_ITER
        >>   40 FOR_ITER                25 (to 68)
             43 STORE_FAST               1 (x1)
             46 LOAD_FAST                1 (x1)
             49 GET_ITER
        >>   50 FOR_ITER                12 (to 65)
             53 STORE_FAST               2 (x2)
             56 LOAD_FAST                2 (x2)
             59 LIST_APPEND              3
             62 JUMP_ABSOLUTE           50
        >>   65 JUMP_ABSOLUTE           40
        >>   68 STORE_FAST               3 (y)

  4          71 LOAD_FAST                3 (y)
             74 PRINT_ITEM
             75 PRINT_NEWLINE
             76 LOAD_CONST               0 (None)
             79 RETURN_VALUE
>>>