 INT        42
  110: s    SETITEM
  111: b    BUILD
  112: a    APPEND
  113: g    GET        5
  116: a    APPEND
  117: .    STOP
highest protocol among opcodes = 0

>>> dis(pickle.dumps(x, 1))
    0: ]    EMPTY_LIST
    1: q    BINPUT     0
    3: (    MARK
    4: c        GLOBAL     'copy_reg _reconstructor'
   29: q        BINPUT     1
   31: (        MARK
   32: c            GLOBAL     'pickletools _Example'
   54: q            BINPUT     2
   56: c            GLOBAL     '__builtin__ object'
   76: q            BINPUT     3
   78: N            NONE
   79: t            TUPLE      (MARK at 31)
   80: q        BINPUT     4
   82: R        REDUCE
   83: q        BINPUT     5
   85: }        EMPTY_DICT
   86: q        BINPUT     6
   88: X        BINUNICODE 'value'
   98: q        BINPUT     7
  100: K        BININT1    42
  102: s        SETITEM
  103: b        BUILD
  104: h        BINGET     5
  106: e        APPENDS    (MARK at 3)
  107: .    STOP
highest protocol among opcodes = 1

Try "the canonical" recursive-object test.

>>> L = []
>>> T = L,
>>> L.append(T)
>>> L[0] is T
True
>>> T[0] is L
True
>>> L[0][0] is L
True
>>> T[0][0] is T
True
>>> dis(pickle.dumps(L, 0))
    0: (    MARK
    1: l        LIST       (MARK at 0)
    2: p    PUT        0
    5: (    MARK
    6: g        GET        0
    9: t        TUPLE      (MARK at 5)
   10: p    PUT        1
   13: a    APPEND
   14: .    STOP
highest protocol among opcodes = 0

>>> dis(pickle.dumps(L, 1))
    0: ]    EMPTY_LIST
    1: q    BINPUT     0
    3: (    MARK
    4: h        BINGET     0
    6: t        TUPLE      (MARK at 3)
    7: q    BINPUT     1
    9: a    APPEND
   10: .    STOP
highest protocol among opcodes = 1

Note that, in the protocol 0 pickle of the recursive tuple, the disassembler
has to emulate the stack in order to realize that the POP opcode at 16 gets
rid of the MARK at 0.

>>> dis(pickle.dumps(T, 0))
    0: (    MARK
    1: (        MARK
    2: l            LIST       (MARK at 1)
    3: p        PUT        0
    6: (        MARK
    7: g            GET        0
   10: t            TUPLE      (MARK at 6)
   11: p        PUT        1
   14: a        APPEND
   15: 0        POP
   16: 0        POP        (MARK at 0)
   17: g    GET        1
   20: .    STOP
highest protocol among opcodes = 0

>>> dis(pickle.dumps(T, 1))
    0: (    MARK
    1: ]        EMPTY_LIST
    2: q        BINPUT     0
    4: (        MARK
    5: h            BINGET     0
    7: t            TUPLE      (MARK at 4)
    8: q        BINPUT     1
   10: a        APPEND
   11: 1        POP_MARK   (MARK at 0)
   12: h    BINGET     1
   14: .    STOP
highest protocol among opcodes = 1

Try protocol 2.

>>> dis(pickle.dumps(L, 2))
    0: \x80 PROTO      2
    2: ]    EMPTY_LIST
    3: q    BINPUT     0
    5: h    BINGET     0
    7: \x85 TUPLE1
    8: q    BINPUT     1
   10: a    APPEND
   11: .    STOP
highest protocol among opcodes = 2

>>> dis(pickle.dumps(T, 2))
    0: \x80 PROTO      2
    2: ]    EMPTY_LIST
    3: q    BINPUT     0
    5: h    BINGET     0
    7: \x85 TUPLE1
    8: q    BINPUT     1
   10: a    APPEND
   11: 0    POP
   12: h    BINGET     1
   14: .    STOP
highest protocol among opcodes = 2

Try protocol 3 with annotations:

>>> dis(pickle.dumps(T, 3), annotate=1)
    0: \x80 PROTO      3 Protocol version indicator.
    2: ]    EMPTY_LIST   Push an empty list.
    3: q    BINPUT     0 Store the stack top into the memo.  The stack is not popped.
    5: h    BINGET     0 Read an object from the memo and push it on the stack.
    7: \x85 TUPLE1       Build a one-tuple out of the topmost item on the stack.
    8: q    BINPUT     1 Store the stack top into the memo.  The stack is not popped.
   10: a    APPEND       Append an object to a list.
   11: 0    POP          Discard the top stack item, shrinking the stack by one item.
   12: h    BINGET     1 Read an object from the memo and push it on the stack.
   14: .    STOP         Stop the unpickling machine.
highest protocol among opcodes = 2

a=