How is the __contains__ method of the list class in Python implemented?

Question

Suppose I define the following variables:

mode = \"access\"
allowed_modes = [\"access\", \"read\", \"write\"]

I currently have a type check

Answer 1

Not equivalent since the any requires an extra function call, a generator expression and things.

>>> mode = "access"
>>> allowed_modes =["access", "read", "write"]
>>> 
>>> def f1():
...    mode in allowed_modes
... 
>>> def f2():
...    any(mode == x for x in allowed_modes)
... 
>>> 
>>> 
>>> import dis
>>> dis.dis
dis.dis(          dis.disassemble(  dis.disco(        dis.distb(        
>>> dis.dis(f1)
  2           0 LOAD_GLOBAL              0 (mode)
              3 LOAD_GLOBAL              1 (allowed_modes)
              6 COMPARE_OP               6 (in)
              9 POP_TOP
             10 LOAD_CONST               0 (None)
             13 RETURN_VALUE
>>> dis.dis(f2)
  2           0 LOAD_GLOBAL              0 (any)
              3 LOAD_CONST               1 ( at 0x7fb24a957540, file "", line 2>)
              6 LOAD_CONST               2 ('f2..')
              9 MAKE_FUNCTION            0
             12 LOAD_GLOBAL              1 (allowed_modes)
             15 GET_ITER
             16 CALL_FUNCTION            1 (1 positional, 0 keyword pair)
             19 CALL_FUNCTION            1 (1 positional, 0 keyword pair)
             22 POP_TOP
             23 LOAD_CONST               0 (None)
             26 RETURN_VALUE
>>> 

This is more instructive than the python source for the methods themselves but here is the source of __contains__ for lists and the loop is in C which will probably be faster than a Python loop.

Some timing numbers confirm this.

>>> import timeit
>>> timeit.timeit(f1)
0.18974408798385412
>>> timeit.timeit(f2)
0.7702703149989247
>>>