1. COMPSCI 107 Computer Science Fundamentals
Lecture 03 – Python syntax functions
modules

2. Learning outcomes At the end of this lecture, you should be able to:
Use built-in functions
Format a string to display output
Use functions from the Python API
Use import statements to import modules
Define and call functions that accept arguments and return values
Use keyword arguments for functions
COMPSCI Computer Science Fundamentals

3. Built-in functions
Python provides a wide range of built-in functions, including
round(value [, number of decimal places])
max(value, value [, value …])
min(value, value [, value …])
abs(value)
float(value)
int(value)
str(value)
type(value)
COMPSCI Computer Science Fundamentals

4. Strings and string methods
Strings are defined in the following ways:
'Single Quotes'
"Double Quotes"
'''Triple single quotes''' this string can span multiple lines
Strings have methods that do something with the string data
See Python documentation for the full list of methods
String
method
>>> greeting = 'hello'.capitalize()
>>> print(greeting)
Hello
COMPSCI Computer Science Fundamentals

5. https://docs.python.org/3/library/string.html#formatstrings
Formatting strings
str.format(args)
where str contains a replacement field surrounded by {}
Can format numbers in a variety of ways
>>> name = 'Andrew'
>>> greeting = 'Hello, my name is {}'.format(name)
>>> print(greeting)
Hello, my name is Andrew
>>> 'Hello {} {}'.format(first, last)
'Hello Andrew Luxton-Reilly'
>>> '{}'.format(math.pi)
' ‘
>>> '{:.2f}'.format(math.pi)
'3.14'
COMPSCI Computer Science Fundamentals

6. Exercise
The following example shows how to print out a floating point value as a percentage:
Given the following values:
Complete the python statement that will print out the marks as a percentage , to 2 decimal places
>>> '{:.5%}'.format(math.pi)
' %'
>>> total = 35
>>> marks = 13
>>> print( )
COMPSCI Computer Science Fundamentals

7. Importing modules Code is stored in modules
We want to reuse code as much as possible
Build up libraries of code
Importing a module allows you to access code in that module
Python.org has a list of all the modules and functions provided
>>> import math
>>> math.pi
>>> math.sqrt(4)
2.0
COMPSCI Computer Science Fundamentals

8. Exercises
Write a program to read the radius of a circle from the user, and print out the circumference of a circle with the input radius.
Note: circumference = 2πr
COMPSCI Computer Science Fundamentals

9. Functions
A function is a sequence of instructions designed to perform a task, and is packaged as a unit.
Functions have a name
Functions accept arguments
Functions return values
Syntax
Indentation rather than braces are used to signify blocks of code
Variables defined within the scope of a function are not available outside the function
def rectangle_area(width, height):
return width * height
COMPSCI Computer Science Fundamentals

10. Functions without a return value
Some functions perform a task that doesn’t evaluate to a value
Functions that don’t explicitly return a value will evaluate to None
def print_greeting():
print('Hello')
print('How are you?')
def print_named_greeting(name):
print('Hello', name)
print('How are you?')
>>> x = print_greeting()
Hello
How are you?
>>> print(x)
None
COMPSCI Computer Science Fundamentals

11. Functions with a return value
Most functions return a value
Use the return keyword
def calculate_sum(a, b):
return a + b
import math
def point_inside(centre_x, centre_y, radius, point_x, point_y):
EPSILON =
dx = abs(centre_x - point_x)
dy = abs(centre_y - point_y)
hyp = math.sqrt(dx **2 + dy **2)
return hyp < radius + EPSILON
COMPSCI Computer Science Fundamentals

12. Exercises
Write a function called triangle_area(base, height) that returns the area of a triangle given the base and the height.
height
base
COMPSCI Computer Science Fundamentals

13. Calling functions with keyword arguments
Functions are called by passing a value for each parameter
Order of the values matches the order of parameters
You may use the name of the parameter when you pass the values
If you use the name, then you can pass the values in any order
def greeting(name, message):
print('Hello {}. {}'.format(name, message))
>>> greeting('Andrew', 'Welcome to COMPSCI 107')
Hello Andrew. Welcome to COMPSCI 107
>>> greeting(name = 'Andrew', message = 'Welcome to COMPSCI 107')
>>> greeting(message = 'Welcome to COMPSCI 107', name = 'Andrew')
COMPSCI Computer Science Fundamentals

14. print() keyword arguments
print('a', 'b', 'c')
is the same as
print('a', 'b', 'c', sep=' ', end='\n')
>>> print('a', 'b', 'c', sep=' ', end='\n')
a b c
>>> print('a', 'b', 'c', sep='', end='\n')
abc
>>> print('a', 'b', 'c', sep='---', end='!')
a---b---c!
COMPSCI Computer Science Fundamentals

15. Exercises What is the output when the following program is executed?
print('a', end='')
print('b', 'c', sep='--')
print('d')
COMPSCI Computer Science Fundamentals

16. Functions with default values
Consider the following function:
Values are required for all parameters listed in the definition
If we provide a default value in the definition, then we don’t need a value for that parameter when we call the function
def greeting(name, message):
print('Hello {}. {}'.format(name, message))
>>> greeting('Andrew', 'Welcome to COMPSCI 107')
Hello Andrew. Welcome to COMPSCI 107
def greeting(name, message='How are you?'):
print('Hello {}. {}'.format(name, message))
>>> greeting('Andrew', 'Welcome to COMPSCI 107')
Hello Andrew. Welcome to COMPSCI 107
>>> greeting('Andrew')
Hello Andrew. How are you?
COMPSCI Computer Science Fundamentals

17. Summary
Code can be more easily reused when it is placed in a function or module
Modules may be imported to access the functions stored in them
Functions may have parameters
Parameters may have default values
Functions can be called without passing values to parameters that have default values
COMPSCI Computer Science Fundamentals