Clean way to write IF statements in python to skip on None?

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I have a function where sometimes a parameter can be none, and I would like to compare that with another object. However, if I am trying to call an object property, my script will throw an exception on None, even if both objects are None (see example below).

def do_animals_make_same_sound(first_animal, second_animal):
    if first_animal.sound = second_animal.sound:
        print('Yes they do!')

But if both animals are None, it throws an exception when instead I want it to print('Yes they do!'), but it seems I have to write a really ugly If statement:

def do_animals_make_same_sound(first_animal, second_animal):
    if (first_animal is None and second_animal is None) or (first_animal is not None and first_animal.sound == second_animal.sound):
        print('Yes they do!')

Is there a better way to do this?

following code is clearer IMHO:

def do_animals_make_same_sound(first_animal, second_animal):
    # early return if one of the two animals is missing, ensure both exist
    if not (first_animal and second_animal):
        return
    if first_animal.sound == second_animal.sound:
        print('Yes they do!')

ref: Avoid Else, Return Early

Conditional Statements in Python – Real Python, Master if-statements step-by-step and see how to write complex decision making code Frequently, a program needs to skip over some statements, execute a series of statements when you hit Enter after typing in the print('yes') statement, nothing happens. Python's use of indentation is clean, concise, and consistent. code is broken into small blocks using if and return statement. 1. If update is not ready then this is not required to enter in method just exit from this method. 2. Similarly is force update boolean is false then perform the task in if statement – updating the cache and returning from this method. 3.

It's not great, but one approach can be to use getattr with a default, so None (and anything else without the desired attribute) behaves as if it had the default as the value of its attribute. For example:

if first_animal.sound == second_animal.sound:

can become:

if getattr(first_animal, 'sound', None) == getattr(second_animal, 'sound', None):

I don't actually recommend this, as it silently ignores errors. In real code, I'd almost always let the AttributeError propagate; there is no reasonable scenario in which I'd consider None an acceptable stand-in for "something" where "something" has specific behaviors or attributes; if the caller is passing None, that's almost certainly an error that should not be silently ignored.

8. Compound statements, If all expressions are false, the suite of the else clause, if present, is executed. A continue statement executed in the first suite skips the rest of the suite and goes A way around this is to use None as the default, and explicitly test for it in the  An else statement can be combined with an if statement. An else statement contains the block of code that executes if the conditional expression in the if statement resolves to 0 or a FALSE value. The else statement is an optional statement and there could be at most only one else statement following if.

I think first you have to understand what's the meaning if one of the objects is None. There are basically three scenarios:

  1. One or both objects are None

  2. One or both objects does not have sound attribute

  3. Both have sound attribute

For #1, I'm assuming it should throw an error as there is really no comparison. What your code does is print "Yes they do" if both objects are None.

For #2, you can use what ShadowRanger suggests, If both objects have None as sound property, and your think it is a normal behavior, then use ShadowRanger's solution.

For #3, just do your normal comparison

def do_animals_make_same_sound(first_animal, second_animal):
    if not first_animal or not second_animal:
        print("One of the objects is None")
    elif getattr(first_animal, 'sound', None) == getattr(second_animal, 'sound', None):
        print("Yes, they do!")

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If it's a general enough pattern, I'd use a decorator to catch the None case specifically and process it. That keeps the logic out of the function. But you need to define exactly what None means here... it's a little odd that you can pass None for both, but it's not legal to just pass None for one of them. In any case, a decorator is a great way to abstract out some common logic in a clean way...

def NoNone(f):
    @functools.wraps(f)
    def _no_none_func(*args, **kwargs):
        if args[0] == None and args[1] == None:
            print('Both are None')
            return 
        return f(*args)
    return _no_none_func

@NoNone
def do_animals_make_same_sound(first_animal, second_animal):
    if first_animal.sound == second_animal.sound:
        print('Yes they do!')
    else:
        print("No they don't!")

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6. Conditionals and Loops, Humans share with computers none of these qualities. However, we need efficient ways of telling the computer to do these repetitive tasks; we In the course of doing these repetitive tasks, computers often need to make decisions. Finally, if the elif statement is False, Python skips to the else statement and executes the  On the other hand, it might surprise some programmers that Python behaves this way. When it comes to writing clean and maintainable code, surprising behavior is rarely a good sign.

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Python if elif else, Python if elif else: Python if statement is same as it is with other programming languages. Use the in operator in an if statement; Write an if-else in a single line of code Here is the general form of a one way if statement. There are several good answers on how you can avoid if-else, and I can list my personal favorites: * Guard clauses/statements, as Nihar More describes, or using some assertion/precondition mechanism, where you verify the validity of some assumptio

Comments
  • The problem is, lets says first_animal is defined, but second_animal is None. This technique still throws an errors, because it tried to evaluate second_animal.sound (Which will obviously throw an error if second_animal = None). The decorator seems like what I want, but instead of first_animal.sound == second_animal.sound throwing an error, I just want to be false and print ("No they don't")
  • The point is not to solve this particular problem... the point is that if you want to make your code look clearer, but there is a lot of boilerplate you need to do to validate inputs, you can put that in a separate function and add it as a decorator, and then the decorated function can just focus on what it should do with valid inputs.