# FAQ: Code Challenge: Python Functions - Dog Years

#1

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:

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#2

Hi,

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.
None
Baby, you are 0 years old in dog years.
None

#3

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"
``````

#4

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.
>>>
``````

#5

#6

Some more fun with user input.
I’d like help with setting up another function to make sure only int is entered.
I’d like help with setting up another function to make sure only str is entered.
That way I can call the function each time I ask for user input…

``````def dog_years_input():
"""This functon asks the user for two ints . This will take a string
and an ints.
First is user name, second is number of years. It will calc the dog
years age * 7."""
print("This will take two inputs. First is name and then a number.\nThen it will return the dog years.")
name = str(input("name "))
age = float(input("age int "))
dog_years = age * 7
return name + " you are " + str(dog_years) + " years old in dog years."
#challenge if dog_years < Y  then Z
#challenge make sure str and int are entered!
dog_years_input()
``````