Functions

Question 1

Function

Answer 1

In Python, a function is a named sequence of statements that belong together

Question 2

Form of function

Answer 2

def name(parameters): 
 statements

Question 3

Parameter

Answer 3

In the function definition, the parameter list is known as the formal
parameters.
• This list of parameters describes the values that the function will need to
receive from the caller of the function.
• When you call a function, you must provide values to the formal parameters.
• These values are often called as arguments or actual parameters

Question 4

example of function def

Answer 4

import turtle

# Function definition 
def draw_square(t, sz): 
 """Make turtle t draw a square of with side sz.""" 
 for i in range(4): 
 t.forward(sz) 
 t.left(90) 

# Main program 
wn = turtle.Screen() 
wn.bgcolor("lightgreen") 
alex = turtle.Turtle() 

# Call the function to draw the square with actual values for parameter turtle and side 
draw_square(alex, 50) 

wn.exitonclick()
docstrings
formal parameters
arguments (actual parameters)

Question 5

repeat function as many as we want

Answer 5

import turtle

Function definition
def draw_square(t, sz):
“"”Make turtle t draw a multi-colour square of sz.”””
for i in [‘red’, ‘purple’, ‘hotpink’, ‘blue’]:
t.color(i)
t.forward(sz)
t.left(90)

# Main program 
wn = turtle.Screen() # Set up the window and its attributes 
wn.bgcolor("lightgreen") 

alex = turtle.Turtle() # create tess and set some attributes
alex.pensize(3)

size = 20 # size of the smallest square
for i in range(15):
draw_square(alex, size)
size = size + 10 # increase the size for next time
alex.forward(10) # move tess along a little
alex.right(18) # and give her some extra turn

wn.exitonclick()

Question 6

Fruitfull function

Answer 6

A function that return a value is a fruitful function

Question 7

Example of fruitfull function

Answer 7

# Function definition 
def square(x): 
 """ Calculate and return x2.""" 
 y = x * x 
 return y 

# Main program 
to_square = 10 
result = square(to_square) # need a variable to store the returned value 
print "The result of ", to_square, " squared is ", result

Question 8

Global and local variables

Answer 8

Variables and parameters in a function are local, i.e. they only exist inside
the function and you can’t use them outside the function.

It is not possible for a function to set a local variable to a value, complete its
execution, and then when it is called again next time, recover the local
variable.

• Each call of the function creates new local variables, and their lifetimes
expire when the function returns to the caller.

Question 9

Bad form

Answer 9

# Function definition 
def bad_square(x): 
 y = x ** power # bad form, DO NOT access global variable 
 return y 

# Main program 
power = 2 
result = bad_square(10) 
print result

Question 10

functional decomposition.

Answer 10

• It is important to understand that each of the functions we write can be used
and called from other functions we write.
• This is one of the most important ways that allow us to take a large problem
and break it down into a group of smaller problems.