Python Projects for Beginners a ten-Week Bootcamp Approach to Python Programming

Writing Your First Function

Now that we know what the syntactical structure looks like, let’s go ahead and write our own:

# writing your first function
def printInfo( ): # defines what the function does when called print("Name: John Smith") print("Age: 45") printInfo( ) # calls the function to run printInfo( ) # calls the function again

Go ahead and run the cell. We define a function called printInfo, which prints two lines of information each time it’s called. Below that we call the function twice, which outputs the information two times. It may not seem like a more efficient program, but imagine you needed to output that exact information 20 times in a program. It’s concise and efficient.

Function Stages

In Python there are two stages to each function. The first stage is the function definition. This is where you define the name of the function, any parameters it’s supposed to accept, and what it’s supposed to do in the block of code associated with it. See Figure 5- 2.

Figure 5-2. The two steps of a function life cycle (definition and call)
CHapTeR 5 FUnCTIonS
The second stage is known as the function call. Functions will never run until called, so you can define as many functions as you’d like, but if you never call one of them, then nothing will happen. When you call a function, it will run the block of code within the definition.

UDF vs. Built-in

Without even knowing it, you’ve been using functions this whole time. Functions such as range, print, len, etc., are all known as “built-in” functions. They are included in Python because they serve a specific purpose to help build our applications. Now that we’re learning about functions, we can begin to create our own known as UDFs or “user- defined functions.”

Performing a Calculation

Let’s check out one more example of a basic function, but this time do more than just print inside of the block:

# performing a calculation in a function def calc( ):
x, y = 5, 10 print(x + y) calc( ) # will run the block of code within calc and output 15

Go ahead and run the cell. We’ll get an output of 15 every time we call the calc function here.