Python efficiency of and vs multiple ifs

Question

Is there an efficiency difference between using and in an if statement and using multiple if statements? In other words, is something like

if expr1 == expr2 and         


        

Answer 1

When in doubt, you can check what does python compile your statements in, using dis module:

>>> import dis
>>> def test1():
...     if expr1 == expr2 and expr3==expr4:
...        dostuff()
... 
>>> def test2():
...     if expr1 == expr2:
...        if expr3 == expr4:
...           dostuff()
... 
>>> dis.dis(test1)
  2           0 LOAD_GLOBAL              0 (expr1)
              3 LOAD_GLOBAL              1 (expr2)
              6 COMPARE_OP               2 (==)
              9 JUMP_IF_FALSE           24 (to 36)
             12 POP_TOP             
             13 LOAD_GLOBAL              2 (expr3)
             16 LOAD_GLOBAL              3 (expr4)
             19 COMPARE_OP               2 (==)
             22 JUMP_IF_FALSE           11 (to 36)
             25 POP_TOP             

  3          26 LOAD_GLOBAL              4 (dostuff)
             29 CALL_FUNCTION            0
             32 POP_TOP             
             33 JUMP_FORWARD             1 (to 37)
        >>   36 POP_TOP             
        >>   37 LOAD_CONST               0 (None)
             40 RETURN_VALUE        
>>> dis.dis(test2)
  2           0 LOAD_GLOBAL              0 (expr1)
              3 LOAD_GLOBAL              1 (expr2)
              6 COMPARE_OP               2 (==)
              9 JUMP_IF_FALSE           28 (to 40)
             12 POP_TOP             

  3          13 LOAD_GLOBAL              2 (expr3)
             16 LOAD_GLOBAL              3 (expr4)
             19 COMPARE_OP               2 (==)
             22 JUMP_IF_FALSE           11 (to 36)
             25 POP_TOP             

  4          26 LOAD_GLOBAL              4 (dostuff)
             29 CALL_FUNCTION            0
             32 POP_TOP             
             33 JUMP_ABSOLUTE           41
        >>   36 POP_TOP             
             37 JUMP_FORWARD             1 (to 41)
        >>   40 POP_TOP             
        >>   41 LOAD_CONST               0 (None)
             44 RETURN_VALUE        

So as you can see, at python bytecode level, both statements are same - even while you use single if at first statement, it will do JUMP_IF_FALSE after first comparison.