Is it possible to call a function from within a list comprehension without the overhead of calling the function?

问题

In this trivial example, I want to factor out the i < 5 condition of a list comprehension into it's own function. I also want to eat my cake and have it too, and avoid the overhead of the CALL_FUNCTION bytecode/creating a new frame in the python virtual machine.

Is there any way to factor out the conditions inside of a list comprehension into a new function but somehow get a disassembled result that avoids the large overhead of CALL_FUNCTION?

import dis
import sys
import timeit

def my_filter(n):
    return n < 5

def a():
    # list comprehension with function call
    return [i for i in range(10) if my_filter(i)]

def b():
    # list comprehension without function call
    return [i for i in range(10) if i < 5]

assert a() == b()

>>> sys.version_info[:]
(3, 6, 5, 'final', 0)

>>> timeit.timeit(a)
1.2616060493517098
>>> timeit.timeit(b)
0.685117881097812

>>> dis.dis(a)
  3           0 LOAD_CONST               1 (<code object <listcomp> at 0x0000020F4890B660, file "<stdin>", line 3>)
  # ...

>>> dis.dis(b)
  3           0 LOAD_CONST               1 (<code object <listcomp> at 0x0000020F48A42270, file "<stdin>", line 3>)
  # ...

# list comprehension with function call
# big overhead with that CALL_FUNCTION at address 12
>>> dis.dis(a.__code__.co_consts[1])
3         0 BUILD_LIST               0
          2 LOAD_FAST                0 (.0)
    >>    4 FOR_ITER                16 (to 22)
          6 STORE_FAST               1 (i)
          8 LOAD_GLOBAL              0 (my_filter)
         10 LOAD_FAST                1 (i)
         12 CALL_FUNCTION            1
         14 POP_JUMP_IF_FALSE        4
         16 LOAD_FAST                1 (i)
         18 LIST_APPEND              2
         20 JUMP_ABSOLUTE            4
    >>   22 RETURN_VALUE

# list comprehension without function call
>>> dis.dis(b.__code__.co_consts[1])
3         0 BUILD_LIST               0
          2 LOAD_FAST                0 (.0)
    >>    4 FOR_ITER                16 (to 22)
          6 STORE_FAST               1 (i)
          8 LOAD_FAST                1 (i)
         10 LOAD_CONST               0 (5)
         12 COMPARE_OP               0 (<)
         14 POP_JUMP_IF_FALSE        4
         16 LOAD_FAST                1 (i)
         18 LIST_APPEND              2
         20 JUMP_ABSOLUTE            4
    >>   22 RETURN_VALUE

I'm willing to take a hacky solution that I would never use in production, like somehow replacing the bytecode at run time.

In other words, is it possible to replace a's addresses 8, 10, and 12 with b's 8, 10, and 12 at runtime?

来源：https://stackoverflow.com/questions/57648016/is-it-possible-to-call-a-function-from-within-a-list-comprehension-without-the-o

标签

python

python-3.x

python-3.6

bytecode