Python Operator, No Operator For "not In"

This is a possibly silly question, but looking at the mapping of operators to functions I noticed that there is no function to express the not in operator. At first I thought this

Solution 1:

Another function is not necessary here. not in is the inverse of in, so you have the following mappings:

obj inseq => contains(seq, obj)

obj not inseq => not contains(seq, obj)

You are right this is not consistent with is/is not, since identity tests should be symmetrical. This might be a design artifact.

Solution 2:

You may find the following function and disassembly to be helpful for understanding the operators:

>>> deftest():
        if0in (): passif0notin (): passif0is (): passif0isnot (): passreturnNone>>> dis.dis(test)
  20 LOAD_CONST               1 (0) 
              3 LOAD_CONST               2 (()) 
              6 COMPARE_OP               6 (in) 
              9 POP_JUMP_IF_FALSE       1512 JUMP_FORWARD             0 (to 15) 

  3     >>   15 LOAD_CONST               1 (0) 
             18 LOAD_CONST               3 (()) 
             21 COMPARE_OP               7 (notin) 
             24 POP_JUMP_IF_FALSE       3027 JUMP_FORWARD             0 (to 30) 

  4     >>   30 LOAD_CONST               1 (0) 
             33 LOAD_CONST               4 (()) 
             36 COMPARE_OP               8 (is) 
             39 POP_JUMP_IF_FALSE       4542 JUMP_FORWARD             0 (to 45) 

  5     >>   45 LOAD_CONST               1 (0) 
             48 LOAD_CONST               5 (()) 
             51 COMPARE_OP               9 (isnot) 
             54 POP_JUMP_IF_FALSE       6057 JUMP_FORWARD             0 (to 60) 

  6     >>   60 LOAD_CONST               0 (None) 
             63 RETURN_VALUE         
>>> 

As you can see, there is a difference in each operator; and their codes (in order) are 6, 7, 8, and 9.