FAQ: Code Challenge: Python Functions - Dog Years


This community-built FAQ covers the “Dog Years” exercise from the lesson “Code Challenge: Python Functions”.

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This exercise can be found in the following Codecademy content:

Data Science

FAQs on the exercise Dog Years

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Wondering why the code:

def dog_years(name, age):
print (name + “, you are " + str(age*7) + " years old in dog years.”)

Is returning the result:

Lola, you are 112 years old in dog years.
Baby, you are 0 years old in dog years.


It’s returning none because you are returning a print statement.

But the print is not happening inside the function, but when you call the function.

print(dog_years("Lola", 16))
# dog_years should be replaced by the returned value without print! 

My solution is :

def dog_years(name, age):
  age *= 7
  return name + ", you are " + str(age) + " years old in dog years"


The print statement is executing inside the function, but since it has no return value of its own, the caller sees None coming back (on the return).

Whenever possible, do not print inside a function, but use return and let the caller do the printing, as the above post suggests.

def foo(bar, baz):
    return '{brand} is a very good brand of {product}.'.format(brand=bar, product=baz)

print (foo('Nabob', 'coffee'))    
# Nabob is a very good brand of coffee.

We can do interpolation using format on your return statement…

>>> def dog_years(name, age):
	return '{name}, you are {dog_age} years old in dog years.'.format(name=name, dog_age=age * 7)

>>> print(dog_years("Lola", 16))
Lola, you are 112 years old in dog years.


Thank you both for your patient and helpful explanations