Python Get Property if Object is not None

Question

Is there a Pythonic way to grab a property if an object exists on one line of code? Currently in the code below if someone passes in a None type object the code will break, so I need some clean way to check that it is not None, but on one line of code. C# has the ?. syntax that works really well, so looking for something like that.

class MyClass:
    def __init__():
        self.my_property = "Hello, World!"

def print_class_property(myClassInstance):
    print(myClassInstance???.my_property) # Here is where I need something inline

Answer 1

You can use the built-in function getattr. It allows an optional third argument that will be returned if the object passed in doesn't have the specified attribute. From the docs:

getattr(object, name[, default])

Return the value of the named attribute of object. name must be a string. If the string is the name of one of the object’s attributes, the result is the value of that attribute. For example, getattr(x, 'foobar') is equivalent to x.foobar. If the named attribute does not exist, default is returned if provided, otherwise AttributeError is raised.

Bold emphasis mine.

>>> getattr(None, 'attr', 'default')
'default'

Here's an example pertaining more to your problem:

>>> class Class:
    def __init__(self):
        self.attr = 'attr'

        
>>> def func(obj):
    return getattr(obj, 'attr', 'default')

>>> func(Class())
'attr'
>>> func(None)
'default'

As @juanpa.arrivillaga said in the comments, another common idiom when dealing with cases such as this is to use try/except. See What is the EAFP principle in Python?.