M02 In-Class Exercises

DS 5100 | Summer 2023 | Residential

Exercise 2.1

Define a string with a length >= 6 and print:

• the first three characters of the string
• the last three characters of the string

mystr = 'python'
len(mystr) >= 6

True

print(mystr[:3])
print(mystr[-3:])

pyt
hon

Exercise 2.2

Create a new list and assign three values to it.

Then print the second element from the list.

mylist = []
mylist.append('first')
mylist.append('second')
mylist.append('third')
print(mylist[1])

second

mylist = []
mylist += ['first']
mylist += ['second', 'third']
print(mylist[1])

second

mylist2 = []

mylist2[0] = 'foo'

---------------------------------------------------------------------------
IndexError                                Traceback (most recent call last)
Cell In[2], line 1
----> 1 mylist2[0] = 'foo'

IndexError: list assignment index out of range

mylist = ['first','second','third']
print(mylist[1])

second

Exercise 2.3

Create to a tuple with three values.

Then, try to append a fourth value.

mytuple = 1, 2, 3

mytuple = (1, 2, 3)

mytuple = tuple([1, 2, 3])

mytuple.append(4)

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
Cell In[9], line 1
----> 1 mytuple.append(4)

AttributeError: 'tuple' object has no attribute 'append'

Exercise 2.4

Assign a value to a string.

Assign three string values to a set.

Check if the string is in the set.

val = 'ERROR'
levels = {'WARN','ERROR','CRITICAL'}

val in levels

True

levels = {'WARN','ERROR','CRITICAL','WARN','ERROR','CRITICAL'}

levels

{'CRITICAL', 'ERROR', 'WARN'}

Exercise 2.5

Create a dictionary containing at least three key-value pairs.

Use get() to index into the dictionary with one of the keys to extract the corresponding value.

Then, store the keys in a list and print the list.

name_age = {
    'greg': 15, 
    'annabel': 22, 
    'joaquin': 19
}

print('name_age[joaquin] =', name_age.get('joaquin'))

name_age[joaquin] = 19

names = list(name_age.keys())

print('names:', names)

names: ['greg', 'annabel', 'joaquin']

type(name_age.keys()), type(names)

(dict_keys, list)

Exercise 2.6

Convert the following sentence into a set of lowercase words sorted alphabetically.

Do not include the punction mark in the resulting set.

"The quick brown fox jumped over the lazy dogs."

mystring = "The quick brown fox jumped over the lazy dogs."

mystring1 = mystring.replace('.', '')
mystring2 = mystring1.lower()
mystring3 = mystring2.split()
myset1 = set(mystring3)
myset2 = sorted(myset1)

myset2

['brown', 'dogs', 'fox', 'jumped', 'lazy', 'over', 'quick', 'the']

sorted(mystring3)

sorted(set(mystring.replace('.', '').lower().split())

['brown', 'dogs', 'fox', 'jumped', 'lazy', 'over', 'quick', 'the']

Exercise 2.7

Compare the lengths of the preceding list and set.

If not equal, give the difference.

mylist = mystring.replace('.', '').lower().split()
myset = set(mylist)

len(mylist) == len(myset)

False

abs(len(mylist) - len(myset))

1

Exercise 2.8

Define three variables of any type.

Use an f string to print a string containing each variable name followed by its value, using comma separators between the pairs.

For example:

epoch 1, mode TRAIN, ...

epoch = 1
mode = "TRAIN"
loss = 0.46

print(f"epoch {epoch}, mode {mode}, loss {loss}")

epoch 1, mode TRAIN, loss 0.46

Exercise 2.9

Define two variables, assigning them floating point values.

Write an expression using an operation on the two variables that will produce a value that may be cast as an integer.

Next, use a logical operation that uses the integer that evaluates to False. Print the result with print()

var1 = 1.5
var2 = 20.5
var3 = int(var1 // var2)

var1 // var2

0.0

var3

0

test = var3 < 0

print(test)

False

Exercise 2.10

Write a Python program to print the input string in the format of the output:

Input:

“Twinkle, twinkle, little star, How I wonder what you are! Up above the world so high, Like a diamond in the sky. Twinkle, twinkle, little star, How I wonder what you are”

Output:

Twinkle, twinkle, little star,
    How I wonder what you are! 
        Up above the world so high,         
        Like a diamond in the sky. 
Twinkle, twinkle, little star, 
    How I wonder what you are

Solution 1

print("Twinkle, twinkle, little star, \n\tHow I wonder what you are! \n\t\tUp above the world so high, \n\t\tLike a diamond in the sky. \nTwinkle, twinkle, little star, \n\tHow I wonder what you are!")

Twinkle, twinkle, little star, 
	How I wonder what you are! 
		Up above the world so high, 
		Like a diamond in the sky. 
Twinkle, twinkle, little star, 
	How I wonder what you are!

Solution 2

msg = """
Twinkle, twinkle, little star, 
\tHow I wonder what you are! 
\t\tUp above the world so high, 
\t\tLike a diamond in the sky. 
Twinkle, twinkle, little star, 
\tHow I wonder what you are!
"""

print(msg)

Twinkle, twinkle, little star, 
	How I wonder what you are! 
		Up above the world so high, 
		Like a diamond in the sky. 
Twinkle, twinkle, little star, 
	How I wonder what you are!

Exercise 2.11

Compute a and b as follows:

a = 0.15 + 0.15
b = 0.1 + 0.2

Test to see if a and b are equal.

a = 0.15 + 0.15
b = 0.1 + 0.2

a == b

False

a, b

(0.3, 0.30000000000000004)

What is going on? Floating point comparisons are unreliable because of the way the computer stores their values.

Accoring to The Floating-Point Guide, "Due to rounding errors, most floating-point numbers end up being slightly imprecise."