Week 9 - Functions

# Example 1: implementing a max function from scratch my_list = [1, 7, 3, 6, 9] maximum = my_list[0] for element in my_list: if element > maximum: maximum = element # this is the output of our codes above print(maximum)

max(1, 2, 4, 3)

# Now we use the built-in max(...) function instead # the built-in function max(...) encapsulates all the different steps above into one single command print(max(my_list))

# Define your custom max function! def beta_alpha(my_list): maximum = my_list[0] for element in my_list: if element > maximum: maximum = element return maximum # output of the function

beta_alpha([1, 2, 4, 3])

max([1, 2, 4, 3])

# Example 2: define a function for calculating the area of a circle def circle_area(radius): pi = 3.14159 area = pi * radius **2 return area

# we can call the function like so circle_area(10) # this is a function call

3.14159 * 10 * 10

def dummy_function(): """ This function has no output """ # do something pi = 3.14

dummy_function()

# function with no outputs result = print("I am Kevin")

result

# the function definition includes many important parts def circle_area(radius): # function header, starts with the 'def' keyword # The body of a function is indented pi = 3.14159 # if there is no return statement, the function would return None return pi * radius * radius # the return statement sends back an output value to the function call

def cylinder_volume(radius, height): """ This function computes the volume of a cylinder Args: - radius - height """ pi = 3.14159 return pi * radius * radius * height

# adding docstring cylinder_volume(10, 1)

def do_something(arg1, arg2): summation = arg1 + arg2 return summation

do_something(11, 2)

def do_something(arg1, arg2): addition = arg1 + arg2 multiplication = arg1 * arg2 return (addition, multiplication)

do_something(11, 2)

# you can unpack the tuple summation, product = do_something(1, 2)

type(do_something(1, 2))

product

# Print vs. Return in Functions # Here are two valid functions. One returns a value and one simply prints a value, without returning anything. def print1(text1, text2): """ This function only prints a text to the console Args: - text1 - text2 """ print(text1 + " and " + text2) # this function returns no output def print2(text1, text2): """ This function returns something """ return text1 + " and " + text2

dummy1 = print1("Anna", "Bernard") # which goes to argument 1 and argument 2? dummy2 = print2("Anna", "Bernard")

print(dummy1)

dummy2

print("print1 returns the value: {}".format(dummy1)) print("print2 returns the value: {}".format(dummy2))

# assigning it to a value suppress the output (only in Notebook) print1("Anna", "Bernard")

# Example 3: using default arguments in a function def circle_area(radius = 1): # we can specify a default value for the argument """ This function calculates the area of a circle given radius. If user does not specify a value for the radius, the default value is used """ pi = 3.14159 return pi * radius * radius

print(circle_area(1))

print(circle_area()) # this is the same as calling the function with radius = 1

# passing the radius argument by position print(circle_area(10)) # override the default value of 1

# passing the radius argument by name print(circle_area(radius = 10))

def cylinder_volume(radius, height): pi = 3.14159 return pi * radius * radius * height

cylinder_volume(1, 2)

cylinder_volume(height = 1, radius = 2)

%run -i students.py

# Exercise 1: write a function to compute population density # <your code here> (~ 2 lines) def population_density(population, area): return population/area # test cases for your function medan_population = population_density(2068000, 261) expected_result1 = 2068000/261. print("expected result: {}, actual result: {}".format(expected_result1, medan_population))

# integer division 8 // 7

# modulo operator 8 % 7

# Exercise 2: write a function that takes an integer number of days # and return a string with the number of weeks and days that is. def timedelta(days): number_of_weeks = days // 7 number_of_days = days % 7 return "{} week(s) and {} day(s).".format(number_of_weeks, number_of_days)

# test your function print(timedelta(8)) # should return 1 week and 1 day print(timedelta(10)) # should return 1 week and 3 days

# give an example of an assignment statement size = 7

# give an example of a for loop for _ in range(10): print("repeat")

# give an example of a method call # a method is a function that belongs to an object "Hello World".lower()

# give an example of a while loop numbers = list(range(10)) while len(numbers) > 0: numbers.pop() print(numbers)

# give an example of a built-in function # what is the name of the function? # what is the argument to the function? range(10) # range is the name, 10 is the argument

# give an example of a function that is called with no argument list()

def my_function(): some_variable = 1 # this is a local variable print(some_variable)

my_function()

def happy_function(): some_variable = "Hello" return some_variable

my_function()

some_variable = 0 # some_variable is a global variable here def my_function(): # accessing a global variable from inside a function is OK print(some_variable)

my_function()

print(some_variable)

# Case study: what happens if we try to modify a global variable inside a function? balance = 0 # this is a global variable def top_up(): balance += 20 def print_balance(): print(balance) print_balance()

# Case study: what happens if we try to modify a global variable inside a function? # If you want to change the global variable balance, pass it as an argument balance = 0 def top_up(balance): # the correct way to write the top_up function is by passing the balance as an argument balance += 20 return balance balance = top_up(balance) print(balance)

# Quiz 2.1: what is printed by the following str1 = 'Hello World' def print_fn(): str1 = 'Hello There' print(str1) print_fn() # Question: what is printed? # A. "Hello World" # B. "Hello There" # C. Nothing is printed

# Quiz 2.2: what is printed by the following str1 = 'Hello World' def print_fn(): #str1 = 'Hello There' print(str1) print_fn() # Question: what is printed? # A. Hello World # B. Hello There # C. An error occurs