How to create an ’empty if statement’ in python

by

There is a performance improvement if there isn’t an else case in the “if”, since the bytecodes don’t pass execution into the “if” case.

Here’s some functions and the output of dis.dis(foo)

The following sample app: 

def foo(x):
    if x:
        pass
    else:
        return x+2

Disassembles to:

5           0 LOAD_FAST                0 (x)
            3 POP_JUMP_IF_FALSE        9

6           6 JUMP_FORWARD             8 (to 17)

8     >>    9 LOAD_FAST                0 (x)
           12 LOAD_CONST               1 (2)
           15 BINARY_ADD          
           16 RETURN_VALUE        
      >>   17 LOAD_CONST               0 (None)
           20 RETURN_VALUE

The following

def foo(x):
    if not x:
        return x+2

Disassembles to:

11           0 LOAD_FAST                0 (x)
             3 POP_JUMP_IF_TRUE        14

12           6 LOAD_FAST                0 (x)
             9 LOAD_CONST               1 (2)
            12 BINARY_ADD          
            13 RETURN_VALUE        
       >>   14 LOAD_CONST               0 (None)

More Related Contents:

  1. Keyword If Statements [closed]
  2. Python Code that returns true while key is pressed down false if release?
  3. More ‘Pythonic’ way to write asymmetric if-else statement
  4. How to test multiple variables for equality against a single value?
  5. Why does python use ‘else’ after for and while loops?
  6. Else clause on Python while statement
  7. if else in a list comprehension [duplicate]
  8. What’s the scope of a variable initialized in an if statement?
  9. Better to ‘try’ something and catch the exception or test if it’s possible first to avoid an exception?
  10. Compare two columns using pandas
  11. Difference between multiple if’s and elif’s?
  12. What is a None value?
  13. if x:, vs if x == True, vs if x is True
  14. Putting an if-elif-else statement on one line?
  15. How to check if a string contains an element from a list in Python
  16. How to write inline if statement for print?
  17. What does a semicolon do?
  18. Can you make multiple “if” conditions in Python? [duplicate]
  19. Pythonic way to combine for-loop and if-statement
  20. How to have multiple conditions for one if statement in python [duplicate]
  21. Too many if statements
  22. Comparing numbers give the wrong result in Python
  23. One line if-condition-assignment
  24. Python “if X == Y and Z” syntax
  25. How do “and” and “or” work when combined in one statement? [duplicate]
  26. Elif and if not working or me not understanding [duplicate]
  27. Pythonic way to avoid “if x: return x” statements
  28. Python: check if an object is a sequence
  29. What is the recommended way to break a long if statement? (W504 line break after binary operator)
  30. Creating a Python list comprehension with an if and break

Leave a Comment