📝Week 4 - Lab Intro

In this lab introduction we will briefly revisit the topic of functions from lecture, and then go over an introduction to image processing using Numpy, the topic of today’s lab.

Functions

Defining a function

A function is defined using the def keyword. All code within the function must be indented.

def myfunc():
    x = 300
    print(x)

Calling a function

To run the code within a function, we can write the name of a function followed by parentheses. This is called “calling the function.” The code below can be used to call the myfunc function.

myfunc()

300

Function inputs

A function can be given input arguments which are included within the parentheses of the function definition.

def dbl(x):
    print(2 * x)

When you call a function that requires arguments, the input is included in the parantheses of the function call.

dbl(6)

12

Function outputs

A function can output data by using the return keyword. After the return statement, the function is exited immediately, so no indented code below the return statement gets run.

def square(x):
    return x**2

Notice that the square function doesn’t print, it returns an output value which can then be stored in a variable.

y = square(3)
print(y)

9

Multiple inputs and outputs

Functions can have multiple inputs and outputs, separated by commas. The example function below takes in two inputs, a rectangle’s length and width, and it returns the rectangle’s area and perimeter.

def area_and_perim(length, width):
    area = length * width
    perim = (length + width) * 2
    return area, perim

print(area_and_perim(3,4))

(12, 14)

Image Processing in Python

We will now go over a brief introduction to image processing in Python, which can be found at the top of today’s lab assignment.