Python optimization levels

example.py

"""\
DOCSTRING\
"""

print(__doc__)

if __debug__:
    print("DEBUGGING")

if not __debug__:
    print("OPTIMIZING")

assert False, "ASSERT"

opt-0

# python3.11 -m dis example.py

  0           0 RESUME                   0

  1           2 LOAD_CONST               0 ('DOCSTRING')
              4 STORE_NAME               0 (__doc__)

  5           6 PUSH_NULL
              8 LOAD_NAME                1 (print)
             10 LOAD_NAME                0 (__doc__)
             12 PRECALL                  1
             16 CALL                     1
             26 POP_TOP

  7          28 NOP

  8          30 PUSH_NULL
             32 LOAD_NAME                1 (print)
             34 LOAD_CONST               2 ('DEBUGGING')
             36 PRECALL                  1
             40 CALL                     1
             50 POP_TOP

 10          52 NOP











 13          54 LOAD_ASSERTION_ERROR
             56 LOAD_CONST               5 ('ASSERT')
             58 PRECALL                  0
             62 CALL                     0
             72 RAISE_VARARGS            1

opt-1

# python3.11 -O -m dis example.py

  0           0 RESUME                   0

  1           2 LOAD_CONST               0 ('DOCSTRING')
              4 STORE_NAME               0 (__doc__)

  5           6 PUSH_NULL
              8 LOAD_NAME                1 (print)
             10 LOAD_NAME                0 (__doc__)
             12 PRECALL                  1
             16 CALL                     1
             26 POP_TOP

  7          28 NOP








 10          30 NOP

 11          32 PUSH_NULL
             34 LOAD_NAME                1 (print)
             36 LOAD_CONST               4 ('OPTIMIZING')
             38 PRECALL                  1
             42 CALL                     1
             52 POP_TOP
             54 LOAD_CONST               5 (None)
             56 RETURN_VALUE

opt-2

# python3.11 -OO -m dis example.py

  0           0 RESUME                   0

  1           2 NOP


  5           4 PUSH_NULL
              6 LOAD_NAME                0 (print)
              8 LOAD_NAME                1 (__doc__)
             10 PRECALL                  1
             14 CALL                     1
             24 POP_TOP

  7          26 NOP








 10          28 NOP

 11          30 PUSH_NULL
             32 LOAD_NAME                0 (print)
             34 LOAD_CONST               3 ('OPTIMIZING')
             36 PRECALL                  1
             40 CALL                     1
             50 POP_TOP
             52 LOAD_CONST               4 (None)
             54 RETURN_VALUE

side-by-side

# pr --omit-pagination --merge --page-width=180 opt-[012]

# python3.11 -m dis example.py				    # python3.11 -O -m dis example.py				# python3.11 -OO -m dis example.py
							    								
  0	      0 RESUME			 0		      0		  0 RESUME		     0			  0	      0 RESUME			 0
							    								
  1	      2 LOAD_CONST		 0 ('DOCSTRING')      1		  2 LOAD_CONST		     0 ('DOCSTRING')	  1	      2 NOP
	      4 STORE_NAME		 0 (__doc__)	    		  4 STORE_NAME		     0 (__doc__)	
							    								
  5	      6 PUSH_NULL				      5		  6 PUSH_NULL					  5	      4 PUSH_NULL
	      8 LOAD_NAME		 1 (print)	    		  8 LOAD_NAME		     1 (print)			      6 LOAD_NAME		 0 (print)
	     10 LOAD_NAME		 0 (__doc__)	    		 10 LOAD_NAME		     0 (__doc__)		      8 LOAD_NAME		 1 (__doc__)
	     12 PRECALL			 1		    		 12 PRECALL		     1				     10 PRECALL			 1
	     16 CALL			 1		    		 16 CALL		     1				     14 CALL			 1
	     26 POP_TOP					    		 26 POP_TOP						     24 POP_TOP
							    								
  7	     28 NOP					      7		 28 NOP						  7	     26 NOP
							    								
  8	     30 PUSH_NULL				    								
	     32 LOAD_NAME		 1 (print)	    								
	     34 LOAD_CONST		 2 ('DEBUGGING')    								
	     36 PRECALL			 1		    								
	     40 CALL			 1		    								
	     50 POP_TOP					    								
							    								
 10	     52 NOP					     10		 30 NOP						 10	     28 NOP
							    								
							     11		 32 PUSH_NULL					 11	     30 PUSH_NULL
							    		 34 LOAD_NAME		     1 (print)			     32 LOAD_NAME		 0 (print)
							    		 36 LOAD_CONST		     4 ('OPTIMIZING')		     34 LOAD_CONST		 3 ('OPTIMIZING')
							    		 38 PRECALL		     1				     36 PRECALL			 1
							    		 42 CALL		     1				     40 CALL			 1
							    		 52 POP_TOP						     50 POP_TOP
							    		 54 LOAD_CONST		     5 (None)			     52 LOAD_CONST		 4 (None)
							    		 56 RETURN_VALUE					     54 RETURN_VALUE
							    								
							    								
 13	     54 LOAD_ASSERTION_ERROR			    								
	     56 LOAD_CONST		 5 ('ASSERT')	    								
	     58 PRECALL			 0		    								
	     62 CALL			 0		    								
	     72 RAISE_VARARGS		 1