Functions

Workshop 2 – Interactive classroom

More on Functions

So far, we have used functions from python or other packages, such as numpy, to perform a generic task. What if there is no function for a specific task you need to carry out? If you anticipate that you will need to carry out the task again in the future, just write your own function! Moreover, if the program you’re coding is complex, it is good coding practice to partition your program into individual chunks of code (i.e., your own functions). This will help future readers substantially to understand your program.

So let’s write our first own functions!

def years2days():
    print("One year has 365 days!")

years2days()

One year has 365 days!

Let’s make it more useful..

def years2days(years):
    days = years * 365
    return days

days = years2days(2)
print(days)

And let’s write a brief statement of what our function does into the docstring that we learned about earlier:

def years2days(years):
    """
    Convert Years to Days

    This function takes a number of years as input and calculates the equivalent number of days.
    """
    days = years * 365
    return days

#02-05: Functions for time conversion

Open the file 02_workshop/time_conversion.py and execute the function definition of our function years2days()
What happens if you execute years2days??
Write your own function days2hours() into the same file.
Write your own function years2hours() into the same file and re-use the previous two functions in the conversion.

We have already used functions that took more than one argument. Let’s modify our function years2days() in a way that a user could specify the number of leap years that happened in the given time period.

def years2days(years, n_leapyears=0):
    days = (years * 365) + n_leapyears
    return days

print(years2days(1))
print(years2days(1, n_leapyears=1))
print(years2days(1, 1))

365
366
366

The above implementation of our function makes use of two types of function arguments. years is a positional argument. It is called this way, because its position matters (it has to be the first argument provided to the function), and it is required for the function to run successfully. n_leapyears is called a keyword argument, and it is defined as a pair (keyword_argument=<default_value>). The value provided with the keyword argument is a default value, so that the user can specify the number of leap years but does not have to. In case the user only provides input for years, the function assumes n_leapyears equal to 0. Keyword arguments can either be provided to the function at the correct position, or by providing the keyword–value pair.

Learning checklist

I can write my own functions and document their purpose with a docstring.
I know how to pass arguments to functions and I know how to return variables from functions.
I know the difference between positional and keyword arguments, and I know how to specify a default value for a function that I coded myself.