Python Equality Check Difference

Question

Suppose we want some block of code to be executed when both \'a\' and \'b\' are equal to say 5. Then we can write like :

if a == 5 and b == 5:
    # do something         


        

Answer 1

As far as integers are concerned, there is no difference, in terms of sheer performance, between the first two comparisons.

The third comparison is different, though; since a little more fiddling with the stack gets involved. Indeed, the code

import dis

def comparison_1(a, b):
    if a == 5 and b == 5:
        pass

def comparison_2(a, b):
    if a == b and b == 5:
        pass

def comparison_3(a, b):
    if a == b == 5:
        pass

print("*** First comparison ***")
dis.dis(comparison_1)

print("\n*** Second comparison ***")
dis.dis(comparison_2)

print("\n*** Third comparison ***")
dis.dis(comparison_3)

returns

*** First comparison ***
  4           0 LOAD_FAST                0 (a)
              3 LOAD_CONST               1 (5)
              6 COMPARE_OP               2 (==)
              9 POP_JUMP_IF_FALSE       27
             12 LOAD_FAST                1 (b)
             15 LOAD_CONST               1 (5)
             18 COMPARE_OP               2 (==)
             21 POP_JUMP_IF_FALSE       27

  5          24 JUMP_FORWARD             0 (to 27)
        >>   27 LOAD_CONST               0 (None)
             30 RETURN_VALUE        

*** Second comparison ***
  8           0 LOAD_FAST                0 (a)
              3 LOAD_FAST                1 (b)
              6 COMPARE_OP               2 (==)
              9 POP_JUMP_IF_FALSE       27
             12 LOAD_FAST                1 (b)
             15 LOAD_CONST               1 (5)
             18 COMPARE_OP               2 (==)
             21 POP_JUMP_IF_FALSE       27

  9          24 JUMP_FORWARD             0 (to 27)
        >>   27 LOAD_CONST               0 (None)
             30 RETURN_VALUE        

*** Third comparison ***
 12           0 LOAD_FAST                0 (a)
              3 LOAD_FAST                1 (b)
              6 DUP_TOP             
              7 ROT_THREE           
              8 COMPARE_OP               2 (==)
             11 JUMP_IF_FALSE_OR_POP    23
             14 LOAD_CONST               1 (5)
             17 COMPARE_OP               2 (==)
             20 JUMP_FORWARD             2 (to 25)
        >>   23 ROT_TWO             
             24 POP_TOP             
        >>   25 POP_JUMP_IF_FALSE       31

 13          28 JUMP_FORWARD             0 (to 31)
        >>   31 LOAD_CONST               0 (None)
             34 RETURN_VALUE