Why should functions always return the same type?

by

Why should functions return values of a consistent type? To meet the following two rules.

Rule 1 — a function has a “type” — inputs mapped to outputs. It must return a consistent type of result, or it isn’t a function. It’s a mess.

Mathematically, we say some function, F, is a mapping from domain, D, to range, R. F: D -> R. The domain and range form the “type” of the function. The input types and the result type are as essential to the definition of the function as is the name or the body.

Rule 2 — when you have a “problem” or can’t return a proper result, raise an exception.

def x(foo):
    if 'bar' in foo:
        return (foo, 'bar')
     raise Exception( "oh, dear me." )

You can break the above rules, but the cost of long-term maintainability and comprehensibility is astronomical.

“Wouldn’t it be cheaper memory wise to return a None?” Wrong question.

The point is not to optimize memory at the cost of clear, readable, obvious code.

More Related Contents:

  1. How function is getting called without defining in python [closed]
  2. How to call functions in python
  3. Check if input is empty
  4. Why does my recursive function return None?
  5. Passing an integer by reference in Python
  6. Run function from the command line
  7. Is there a math nCr function in python? [duplicate]
  8. Call a function with argument list in python
  9. How to plot multiple functions on the same figure, in Matplotlib?
  10. Best way to check function arguments? [closed]
  11. How to call function that takes an argument in a Django template?
  12. How are Python in-place operator functions different than the standard operator functions?
  13. Python: return the index of the first element of a list which makes a passed function true
  14. Is it possible to run function in a subprocess without threading or writing a separate file/script.
  15. What does a semicolon do?
  16. Basic explanation of python functions
  17. python: how to get information about a function?
  18. What is first class function in Python
  19. In Python, when should I use a function instead of a method?
  20. Python Turtle.Terminator even after using exitonclick()
  21. Tkinter PIL image not displaying inside of a function
  22. Returning multiple values from pandas apply on a DataFrame
  23. Python: Name resolution; order of function def’s
  24. python function default parameter is evaluated only once? [duplicate]
  25. Python modules with submodules and functions
  26. How to plot multiple functions on the same figure
  27. Python – how does passing values work?
  28. Python how to get the calling function (not just its name)?
  29. Correct Use Of Global Variables In Python 3
  30. Store functions in list and call them later [duplicate]

Leave a Comment