Block 3 Part 2 - Python Code

Question 1

Create the following list as a variable:

a_list

items: 1, 10, 23, 2

Answer 1

a_list = [1, 10, 23, 2]

Question 2

Check the length of the list.

Answer 2

len(a_list)

Question 3

Add the number 5 to the end of the list.

Answer 3

a_list = a_list + [5]

Question 4

Check the value of the last element in a_list.

Answer 4

a_list[len(a_list) - 1]

Question 5

Display a_list on the screen

Answer 5

a_list

Question 6

True or false?

Dictionaries – just like any other data items – are objects with an id, type and value.

Answer 6

True

Question 6

Here is an example of a Python dictionary:

mini_dictionary = {‘train’: ‘A powered
railway vehicle’, ‘bicycle’:
‘A vehicle consisting of
two wheels’}

Look at the syntax.
What’s different in a dictionary to a list?

How many key-value pairs does this dictionary have?

Answer 6

Item are surrounded by {} instead of brackets.
Word has apostrophes, e.g. ‘word’.

It has two key-value pairs:
train + definition
bicycle + definition

Question 6

True or false?

Dictionaries have something in common with lists: they are both containers.

Answer 6

True

Question 7

Can we create an empty dictionary?

Answer 7

Yes - it might look something like this:

train_types = {}

Question 8

Adding items to a Python dictionary

Once you have initialised the dictionary
e.g. population_millions = {}
Use the following code in the shell to add key-value pairs.

population_millions[k___] = v_____

Answer 8

key
value

Question 9

Accessing dictionary values

For accessing the values of a dictionary, you can use the k_____, just like you can use an index to access an item in a list.

For instance, in order to access the item with the key key from dictionary population_millions, use:

population_millions[key]

Q: What would you type if you wanted to
access the input for the USA?

Q: What output would you get?

Answer 9

keys
population_millions[‘USA’]
319 (As per my previous input)

Question 10

True or false?

Strings are not case-sensitive, so when accessing dictionary items it’s okay if you write, for example, ‘india’, rather than ‘India’.

Answer 10

False - they are case sensitive so be sure to write it correctly.

Question 11

Amending a dictionary

To amend a dictionary entry, simply type it in again.

E.g. First entry
population_millions[‘France’] = 670

correct to 67, type again
population_millions[‘France’] = 67

It simply o_________ the previous value.

Answer 11

overwrites

Question 12

Checking for a key

Sometimes it is useful to check whether a dictionary contains a particular key, before you try to access the value via that key. Why? If a key doesn’t exist, using the key results in an e______ message. If you are using the key in a program, the execution of the program will s_____.

Answer 12

error message
stop

Question 13

Checking for a key

To check for a key in a dictionary, use the shell and type the following code:

key in population_millions

e.g. ‘USA’ in population_millions

Q: What output will we get if it is there?

Answer 13

True

Question 14

Random dictionary key selection

Two steps to this:

1. turning the dictionary into a l____ of its
   k____, then
2. picking a r______ item from that list.

Answer 14

a list of its keys
random

Question 15

Converting a dictionary into a list

In Python, you can convert a dictionary into a list by using the list( ) constructor.

For example:
my_dict = {‘a’: 1, ‘b’: 2, ‘c’: 3}

Convert the dictionary keys to a list
keys_list = list(my_dict)

(In shell) keys_list
»> [‘a’, ‘b’, ‘c’]

True or false?
With this step we are only converting the keys to a list, not the values.

Answer 15

True

Question 16

Selecting a random item from a list

To select a random item from a list in Python, you can use the function choice() (after importing the random module).

What is the command to import the ‘random module’?

Answer 16

from random import *

Question 17

Selecting a random item from a list

Note that the function choice() takes a l_____ as its argument.

Answer 17

list

Question 18

Getting user input

To get input from the user, we use the f___________:

input()

It has one argument, which is a s________.

Answer 18

function
string

Question 19

Getting user input

Getting user input is a bit strange in Python.
Look at the following example:

user_input = input(“Enter something: “)

What will actually be stored as user_input will be their answer, not the prompt of ‘Enter something’.

Write an example of this is action.

Answer 19

user_input = input(“Enter something: “)

(once enter has been pressed, shell will pop up with statement,
Enter something:
I enter ‘hello’ in shell.
In shell I type: user_input
I then press enter and ‘hello’ is printed.

Question 20

Getting user input

We would write the algorithm to the following code as:

user_input = input(‘How shall I greet you? ‘)

Algorithm
Set the v_________ user_input to the response to ‘How shall I greet you? ‘

Answer 20

variable

Question 21

The interactive loop pattern

Suppose I wanted to write a program that keeps asking me for input and does something in response to my input.

This problem can be solved by i_____________ the interactive loop pattern.

Answer 21

instantiating

(In this case, instantiate means to fill in the pattern)

Question 22

The interactive loop pattern

The interactive loop pattern can be found
in the course materials, namely in the ‘Problem solving and Python quick r________’.

Answer 22

reference

Question 23

The interactive loop pattern

How would you set a variable called ‘exit’ to false?

a) exit = ‘false’
b) exit = False

Answer 23

b)
We do not need to use a string as Python has Boolean values True and False.

Question 24

The interactive loop pattern

This program will keep asking
for input until the user enters ‘quit’
“””
exit = False
while exit == False:
  user_input = input(‘Type your input here: ‘)
  if user_input == ‘quit’:
    exit = True

What is the preferred Pythonic way of stating this type of condition?

Answer 24

while not exit:

It works because not exit is a Boolean expression. It evaluates to True when exit evaluates to False, and to False when exit evaluates to True (and therefore can replace exit == False).

Question 25

The echo chamber interactive loop