Functions Review¶

Practice¶

Can you write this function in python?

$f(x) = 3x + 2$

In [9]:

def f(x):
    return 3*x+2

Can you use the function to find:

$f(3)$

$f(10)$

$f(44)$

In [15]:

print(f(3))
print(f(10))
print(f(44))

11
32
134

Can you find the mistakes?¶

Function 1¶

In [12]:

# we define the function here
def greater_than_five(n):
    if n > 5:
        return True
        print("n is greater than 5")
    else:
        return False
        print("n is less than 5")
        
# we call the function here        
greater_than_five(5)

Out[12]:

False

Function 2¶

In [ ]:

def add_two_numbers(x,y):
return x+y

add_two_numbers(2,3)

Function 3¶

In [4]:

def long_name(name):
    if len(name) > 10:
    return "Long name"
    else:
    return "Short name"



long_name('taylor')

  File "<ipython-input-4-5104d300944b>", line 3
    return "Long name"
         ^
IndentationError: expected an indented block

Function 4¶

In [8]:

def concat_strings(string1, string2):
    new_string = string1 + string2
return new_string 

find_the_mistake_3('I eat pancakes ', 'for breakfast')

  File "<ipython-input-8-0b69a3dc6eed>", line 3
    return new_string
SyntaxError: 'return' outside function

Function 5¶

In [14]:

def print_all_in_list(x):
    for x in x:
        print(x)

print_all_in_list(['Harvard', 'MIT', 'Colombia', 'Duke', 'AAiT', 'KAIST'])

Harvard
MIT
Colombia
Duke
AAiT
KAIST

Function 6¶

In [24]:

def same_color(color_1, color_2):
    if color_1 == color_2: return True
    else: return False
    
print(same_color('red', 'red'))
print(same_color('blue', 'yellow'))

True
False

Same:

In [25]:

def same_color_2(color_1, color_2):
    if color_1 == color_2: 
        return True
    else: 
        return False
    
print(same_color_2('red', 'red'))
print(same_color_2('blue', 'yellow'))

True
False

Practice Problems:¶

Now use the range function!¶

In [ ]:

# Now use a for loop with range

Now use a while loop!¶

In [ ]:

# While loop

There are many ways to solve the same problem¶

Indexing into a list of lists¶

In [35]:

list_of_lists = [[1 , 2,  3], [4, 5, 6], [7, 8, 9]]


# Same thing as: 
list_of_lists = [[1 , 2, 3], 
                 [4, 5, 6], 
                 [7, 8, 9]]

In [51]:

# What does this return?
list_of_lists[1]

Out[51]:

[11, 12, 13]

In [57]:

# What does this return?
list_of_lists[0]

Out[57]:

[1, 2, 3]

In [58]:

# What does this return?
var = list_of_lists[0]
var[2]

Out[58]:

In [59]:

# What does this return?
list_of_lists[0][2]

Out[59]:

In [7]:

# Let's try a few more:
# Remember:
# list_of_lists = [[1 , 2, 3], 
#                  [4, 5, 6], 
#                  [7, 8, 9]]

In [ ]:

list_of_lists[1][0]

In [ ]:

list_of_lists[[2][-1]]

In [ ]:

list_of_lists[-1][0]

In [ ]:

list_of_lists[-1][-2]

NESTED FOR LOOPS¶

Loop inside of a loop¶

In [2]:

for i in [1,2,3,4,5]:
    for j in [1,2,3,4,5]:
        print(i,j)

What will happen if we just print i?

In [ ]:

What will happen if we just print j? What about len(i)?

In [ ]:

In [17]:

list_of_lists = [[1 , 2,  3], 
                 [4, 5, 6], 
                 [7, 8, 9]]

for lst in list_of_lists:
    print(lst)

[1, 2, 3]
[4, 5, 6]
[7, 8, 9]

How can I print all the numbers one by one?¶

In [18]:

# Use a nested for loop!
for lst in list_of_lists:
    for num in lst:
        print(num)

Practice Problem:¶

Write a function to PRINT every letter in the following strings, one letter at a time¶

In [45]:

list_of_strings = ['nested', 'loops', 'are', 'very', 'useful']

In [47]:

def print_letters(lst):
    # Use a nested for loop!
    pass