Session 4 - Sample Exam Qs

Question 1

Q1:
Question: What type of error is demonstrated by attempting to execute print (‘Welcome to the programming course!)?

Answer 1

A1:
A syntax error (the bracket and close quote are in the wrong places)

Question 2

Q2:
Question: What happens when you try to convert a string input to an integer using int(input(‘Enter a number’)) but enter a string instead of a number?

Answer 2

A2:
You will get an ‘exception’ (Note for the exam we don’t expect you to know what >sort< of exception - just what sort of error it is.

Question 3

Q3:
Question: In the context of exception handling in Python, which keywords are used to catch exceptions that are raised?

Answer 3

A3:
‘try’ and ‘except’

Question 4

Q4:
Question: Given the code snippet
data = input(‘Enter a number: ‘)

followed by

print(int(data)+2), what type of error occurs if the user enters a string like “hello”

Answer 4

A4:
Again, an exception. Note that the error will happen when the data is cast to ‘int’ , not when it is input.

Question 5

Q5:
Question: In a try-except block, what will the following code do if a ValueError occurs?

try:
start = int(input(‘Starting number: ‘))
except ValueError as e:
print(“Would you please give me an actual number next time?”)
print(e)

Answer 5

A5:
It will execute the print statements inside the ‘except’ block: Printing the error message >and< the name of the exception.

Question 6

Q6:
Question: How do you access the error message within an except block?

Answer 6

A6:
Via the ‘e’ variable which will contain the error message.

Question 7

Q7:
Question: Given the function below, what will printNTimes(‘Hello, World!’, 3)

output?

def printNTimes(my_string, n):
for x in range(n):
print(my_string)

Answer 7

A7:
It will print the string ‘Hello World!’ three times

Question 8

Q8:
Question: What will the following Numpy code snippet output, and why?

import numpy as np
a = np.array([1, 2, 3, 4, 5])
print(a[2])

Answer 8

A8:
It will print the number ‘3’. This is the third element in the array (and Python starts indexing at zero)

Question 9

Q9:
Question: Consider the following plotting code. What does it aim to plot, and how can you describe the relationship between x and y?

import matplotlib.pyplot as plt
import numpy as np

x = np.linspace(0, 10, 100)
y = np.sin(x)

plt.plot(x, y)
plt.show()

Answer 9

A9:
It will plot sin(x) as a function of x - in other words a sine wave. There will be 100 points for x values between 0 and 10.

Question 10

Q10:
Question: Analyze the following code snippet that creates a plot. What mistake will prevent the code from executing correctly (plotting y as a function of x)?

import matplotlib.pyplot as plt
import numpy as np

x = np.linspace(-5, 5, 100)
y = x**2

plt.plot(x)
plt.show()

Answer 10

A10
The plot statement should take two arguments: x and y. Here it just gets x and it will just plot the values of x (which will be 100 points in a straight line from -5 to 5)

Question 11

What will be the output of the following code?

my_list = [1, 2, 3]
print(my_list[3])

Answer 11

An IndexError will occur because the index 3 is out of range for the list my_list.

Question 12

Explain the purpose of the range() function in Python and provide an example - (3)

Answer 12

The range() function generates a sequence of numbers within a specified range. It is commonly used for iterating over a sequence of numbers using loops.

Example:

for i in range(5):
print(i)

Question 13

What does the following code snippet do? - (3)

my_dict = {‘a’: 1, ‘b’: 2, ‘c’: 3}
print(my_dict.get(‘d’, 0))

Answer 13

The code will print 0.

The .get() method retrieves the value associated with the specified key (‘d’) in the dictionary (my_dict).

If the key does not exist, it returns the default value specified as the second argument, which is 0 in this case.

Question 14

How do you concatenate two lists in Python? - (3)

Answer 14

You can concatenate two lists using the + operator or the .extend() method. Example:

list1 = [1, 2, 3]
list2 = [4, 5, 6]
concatenated_list = list1 + list2
print(concatenated_list)

This will output [1, 2, 3, 4, 5, 6].

Question 15

What is the purpose of the len() function in Python? - (3)

Answer 15

The len() function returns the number of items in an object. It can be used to get the length of strings, lists, tuples, dictionaries, and other iterable objects.

Example:

python
Copy code
my_string = “Hello”
print(len(my_string)) # Output: 5