Using Objects in Functions

Just like any other data type, we can send an object to a function as an input value. We can also set up a function to create a new object and return it to the main program.

Example

Assume we defined the same Dog class we used on the previous page.

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def make_puppy(parent_1, parent_2):
   puppy_name = parent_1.name[0] + parent_2.name[0]
   cuteness = parent_1.is_cute or parent_2.is_cute

   return Dog(puppy_name, 0, cuteness)

dog_1 = Dog('Spot', 6, True)     # Create one Dog object
dog_2 = Dog('Fleas', 2, False)   # Create another Dog object
new_pet = make_puppy(dog_1, dog_2)  # Call make_puppy and return new Dog
print(new_pet)

Console Output

Name of dog: SF, Age of dog: 0 years

  1. Lines 20 and 21 create two new Dog objects.

  2. Line 22 calls the make_puppy function and sends it dog_1 and dog_2 as arguments.

  3. Line 14 assigns the objects to the parameters parent_1 and parent_2.

  4. Line 15 combines the first letters of the parents’ names to make the string for puppy_name.

  5. Line 16 uses a boolean expression to decide if the puppy is cute.

  6. Line 18 creates and returns a new Dog object.

  7. Control returns to line 22, where the new object is assigned to new_pet.

Object Scope

Within a function, any change made to an object will change the object itself.

In the example above, adding the statement parent_1.name = "Fido" changes the property value in the function AND outside of the function. If we used print(dog_1.name) after calling make_puppy, we would see Fido appear in the console instead of Spot.

parent_1 is NOT a new Dog object. Instead, it is a new label that points to the same set of data as dog_1.

We saw similar behavior with both lists and dictionaries.

Check Your Understanding

Question

Given bob = Pet(), which of the following shows the object bob used as an argument?

  1. feed_pet(bob, lettuce)

  2. def feed_pet(bob, lettuce):

  3. return bob

Question

Which of the following shows the object pet_name used as a parameter?

  1. label_habitat(pet_name, climate, habitat_size)

  2. def label_habitat(pet_name, climate, habitat_size):

  3. return pet_name