Exercise 2 Solutions¶

Question 1¶

matches = [0.6, 0.8, 0.94, 0.2, 0.4]
good_matches = []
for m in matches:
    if m > 0.7:
        good_matches += [m]
good_matches

[0.8, 0.94]

[0.7] + 0.8

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[2], line 1
----> 1 [0.7] + 0.8

TypeError: can only concatenate list (not "float") to list

Question 2¶

sample_matches = [
  ['SAM1', 0.6],
  ['SAM2', 0.8],
  ['SAM3', 0.94],
  ['SAM4', 0.2],
  ['SAM5', 0.4]
  ]
good_samples = []
for s in sample_matches:
    print(s[0], type(s[0]))
    if s[1] > 0.7:
        good_samples += [s[0]]
good_samples

SAM1 <class 'str'>
SAM2 <class 'str'>
SAM3 <class 'str'>
SAM4 <class 'str'>
SAM5 <class 'str'>

['SAM2', 'SAM3']

s = ['SAM1', 0.6]
s[0]

'SAM1'

sample_matches = [
  ['SAM1', 0.6],
  ['SAM2', 0.8],
  ['SAM3', 0.94],
  ['SAM4', 0.2],
  ['SAM5', 0.4]
  ]
good_samples = []
for sample_name, match in sample_matches:
    if match > 0.7:
        good_samples += [sample_name]
good_samples

['SAM2', 'SAM3']

for i, val in enumerate(sample_matches):
    print(i)
    print(val)

0
['SAM1', 0.6]
1
['SAM2', 0.8]
2
['SAM3', 0.94]
3
['SAM4', 0.2]
4
['SAM5', 0.4]

for element in enumerate(sample_matches):
    print(element[0])
    print(element[1])

0
['SAM1', 0.6]
1
['SAM2', 0.8]
2
['SAM3', 0.94]
3
['SAM4', 0.2]
4
['SAM5', 0.4]

(a, b) = (1, 5)
b

5

my_tuple = (1,2,3)

my_tuple[0]

1

my_tuple(0)

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[11], line 1
----> 1 my_tuple(0)

TypeError: 'tuple' object is not callable

[('SAM1', 0.8),]
('SAM1', 0.8, 'SAM2', 0.9)

('SAM1', 0.8, 'SAM2', 0.9)

Question 3¶

def find_good_matches(threshold, match_list):
    good_samples = []
    for sample_name, match in match_list:
        if match > threshold:
            good_samples += [(sample_name, match)]
    return good_samples

find_good_matches(0.7, sample_matches)

[('SAM2', 0.8), ('SAM3', 0.94)]

def square_it(n):
    return n * n

val = square_it(2)

print("val is:", val)

val is: 4

def square_it2(n):
    print(n * n)

val = square_it2(2)

print(type(val))

<class 'NoneType'>

def find_good_matches(threshold, good_match_list):
    """Does something useful"""
    tuple_list = ()
    for s, m in good_match_list:
        if m > threshold:
            tuple_list += ((s, m),)
    return tuple_list

sample_matches = [
  ['SAM1', 0.6],
  ['SAM2', 0.8],
  ['SAM3', 0.94],
  ['SAM4', 0.2],
  ['SAM5', 0.4]
  ]
threshold = 0.7
find_good_matches(threshold, sample_matches)

(('SAM2', 0.8), ('SAM3', 0.94))

Question 4¶

Write a function sum_it(a, b) that takes two numbers, a and b and returns the result of adding them together. Then write a function print_sum(a, b) that takes two numbers, a and b and prints the result of adding the two numbers together. What is the difference between these two functions? Which one returns a value?

def sum_it(a, b):
    return a + b

def print_sum(a, b):
    print(a + b)

the_sum = sum_it(5, 7)
print("the_sum", the_sum)
the_next_sum = sum_it(the_sum, 3)

the_sum 12

print("the_next_sum", the_next_sum)

the_next_sum 15

the_sum = print_sum(5, 7)

the_sum

the_sum = print_sum(5, 7)
print("the_sum", the_sum)
the_next_sum = print_sum(the_sum, 3)

12
the_sum None

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[29], line 3
      1 the_sum = print_sum(5, 7)
      2 print("the_sum", the_sum)
----> 3 the_next_sum = print_sum(the_sum, 3)

Cell In[24], line 2, in print_sum(a, b)
      1 def print_sum(a, b):
----> 2     print(a + b)

TypeError: unsupported operand type(s) for +: 'NoneType' and 'int'

Question 5¶

Write a function double_it that takes a list of numbers and doubles each of them in place.

my_list = [1, 2, 3]
my_list[0] = my_list[0] * 2
my_list[1] = my_list[1] * 2
my_list[2] = my_list[2] * 2
my_list

[2, 4, 6]

for num in my_list:
    num * 2

range(len(my_list))

enumerate(my_list)

# enumerate is an iterator
# so we can do
next(enumerate(my_list))

(0, 2)

print("my_list", my_list)
# get all of the values from the enumerate iterator all at once
list(enumerate(my_list))

my_list [2, 4, 6]

[(0, 2), (1, 4), (2, 6)]

my_students = ['Jean-Carl', 'Sahana', 'Siphemelele', 'Sohail']
print("my_students", my_students)
print(list(enumerate(my_students)))

my_students ['Jean-Carl', 'Sahana', 'Siphemelele', 'Sohail']
[(0, 'Jean-Carl'), (1, 'Sahana'), (2, 'Siphemelele'), (3, 'Sohail')]

int_val, string_val = (0, 'Ghost')
print("int_val", int_val)
print("string_val", string_val)

int_val 0
string_val Ghost

val1, val2 = (1, 2, 3)

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
Cell In[36], line 1
----> 1 val1, val2 = (1, 2, 3)

ValueError: too many values to unpack (expected 2, got 3)

my_students = ['Jean-Carl', 'Sahana', 'Siphemelele', 'Sohail']
print("my_students", my_students)

for i, my_student in enumerate(my_students):
    new_string = 'Student ' + my_student
    my_students[i] = new_string
    
print("my_students now", my_students)

my_students ['Jean-Carl', 'Sahana', 'Siphemelele', 'Sohail']
my_students now ['Student Jean-Carl', 'Student Sahana', 'Student Siphemelele', 'Student Sohail']

my_list = [2, 4, 6]
for i, num in my_list:
    print(i, num)

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[38], line 2
      1 my_list = [2, 4, 6]
----> 2 for i, num in my_list:
      3     print(i, num)

TypeError: cannot unpack non-iterable int object

my_tuple_list = [(1, 2), (3, 4)]
for i, num in my_tuple_list:
    print(i, num)

1 2
3 4

my_tuple_list = [(1, 2), (3, 4), 5]
for i, num in my_tuple_list:
    print(i, num)

1 2
3 4

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[40], line 2
      1 my_tuple_list = [(1, 2), (3, 4), 5]
----> 2 for i, num in my_tuple_list:
      3     print(i, num)

TypeError: cannot unpack non-iterable int object

my_students = ['Jean-Carl', 'Sahana', 'Siphemelele', 'Sohail']
print("my_students", my_students)
name_lengths = []
len(my_students[0])

# how would I print the length of each name in the list

my_students ['Jean-Carl', 'Sahana', 'Siphemelele', 'Sohail']

9

my_students = ['Jean-Carl', 'Sahana', 'Siphemelele', 'Sohail']
for name in my_students:
    print(len(name))

# print the index of the student whose name is Sahana
my_students = ['Jean-Carl', 'Sahana', 'Siphemelele', 'Sohail']
# things to use
# for loop
# enumerate
# name == "Sahana"
# if statement

my_students = ['Jean-Carl', 'Sahana', 'Siphemelele', 'Sohail']

for index, value in enumerate(my_students):
    if value == "Sahana":
        print(index)

my_students = ['Jean-Carl', 'Sahana', 'Siphemelele', 'Sohail']

for index, name in enumerate(my_students):
    if name == "Sohail":
        print(index)

my_students = ['Jean-Carl', 'Sahana', 'Siphemelele', 'Sohail']
print("my_students", my_students)

for index, value in enumerate(my_students):
    new_string = 'Student ' + value
    my_students[index] = new_string
    
print("my_students now", my_students)

my_students ['Jean-Carl', 'Sahana', 'Siphemelele', 'Sohail']
my_students now ['Student Jean-Carl', 'Student Sahana', 'Student Siphemelele', 'Student Sohail']

my_students = ['Jean-Carl', 'Sahana', 'Siphemelele', 'Sohail']
print("my_students", my_students)
new_student_list = []
for index, value in enumerate(my_students):
    new_string = 'Student ' + value
    new_student_list += [new_string]
    
print("my_students now", my_students)
print("new_student_list", new_student_list)

my_students ['Jean-Carl', 'Sahana', 'Siphemelele', 'Sohail']
my_students now ['Jean-Carl', 'Sahana', 'Siphemelele', 'Sohail']
new_student_list ['Student Jean-Carl', 'Student Sahana', 'Student Siphemelele', 'Student Sohail']

my_students = ['Jean-Carl', 'Sahana', 'Siphemelele', 'Sohail']
print("my_students", my_students)

for index, value in enumerate(my_students):
    new_string = 'Student ' + value
    my_students[2] = new_string
    print("index", index, "my_students now", my_students)

print("my_students now", my_students)

my_students ['Jean-Carl', 'Sahana', 'Siphemelele', 'Sohail']
index 0 my_students now ['Jean-Carl', 'Sahana', 'Student Jean-Carl', 'Sohail']
index 1 my_students now ['Jean-Carl', 'Sahana', 'Student Sahana', 'Sohail']
index 2 my_students now ['Jean-Carl', 'Sahana', 'Student Student Sahana', 'Sohail']
index 3 my_students now ['Jean-Carl', 'Sahana', 'Student Sohail', 'Sohail']
my_students now ['Jean-Carl', 'Sahana', 'Student Sohail', 'Sohail']

# this answer gives you clues for question 5
my_students = ['Jean-Carl', 'Sahana', 'Siphemelele', 'Sohail']
print("my_students", my_students)

def update_students(student_list):
    for index, value in enumerate(student_list):
        new_string = 'Student ' + value
        student_list[index] = new_string

new_list = update_students(my_students)

my_students ['Jean-Carl', 'Sahana', 'Siphemelele', 'Sohail']