Chapter 3: The world of variables and operators

Question 1

What is a variable?

Answer 1

Data that we need to store and manipulate in our programs

Question 2

Example of a variable

Answer 2

UserAge (variable) = 0 (initial value)

Question 3

Do you have to give a variable an initial value every time it is created?

Answer 3

YEAH!!

Question 4

Can you change the value of a variable later in the program?

Answer 4

Yes

Question 5

Can multiple variables be defined in one go?

Answer 5

Yes

Question 6

Example of multiple variables

Answer 6

userAge, userName = 33, ‘Amrapali’

Question 7

What is Table, chair = ‘brown’, ‘black’ is equivalent to?

Answer 7

Table = Brown
Table = Black

Question 8

What can a variable name in Python contain?

Answer 8

A variable name in Python can contain

1) Letter (a-z, A-Z)
2) Numbers
3) Underscores

Question 9

Can the first character be a number?

Answer 9

No, the first character cannot be a number. variable name as 2username is invalid.

Question 10

Example of variable names

Answer 10

userAge, user_age, userAge2

Question 11

What words cannot be named as usernames?

Answer 11

Words which have a preassigned meaning to them cannot be used as variable names like input and print.

Question 12

Is username same as userName?

Answer 12

No, because the variable names are case-sensitive

Question 13

What are the two naming conventions for variables?

Answer 13

1) Camel case notation

2) Using underscores

Question 14

What is camel case notation? Provide examples

Answer 14

Writing compound words with mixed casing. For example thisIsAVariableName

Question 15

Example of underscore usage in naming a variable

Answer 15

this _is_a_variable_name

Question 16

What is unique about ‘=’ in Python and math?

Answer 16

It has a different meaning in Python and math.

Question 17

What is the ‘=’ sign called in programming?

Answer 17

It is called the assignment operator

Question 18

What does the assignment operator mean?

Answer 18

It means we are assigning the value on the right side of the = sign to the variable on the left

Question 19

If you type the below code into your IDLE editor
X= 5
Y= 10
X=Y
print ("X=", X)
print ("Y=", Y)

What will be the output? Explain.

Answer 19

X= 10
Y= 10
Because, the third line assigns Y’s value to X

Question 20

What are the basic operators in Python?

Answer 20

Addition, subtraction, multiplication, division, floor division, modulus and exponent

Question 21

Provide examples of all the basic operators

Answer 21

x=5
y=2
Addition:
x+y=7

Subtraction:
x-y=3

Multiplication:
x*y= 10

Division:
x/y= 2.5

Floor Division:
x//y=2 (it rounds down the answer to the nearest whole number)

Modulus:
x%y=1 (gives the remainder when 5 is divided by 2)

Exponent:
x**y=25 (5 to the power 2)

Question 22

What are the other assignment operators beside “=’?

Answer 22

+=, -= and *=

Question 23

What does += implies?

Answer 23

If x= 10 then x+=2 i.e. x= x+2

the output will be x= 12

Question 24

What does x-= implies?

Answer 24

If x= 10 then x-=2 i.e. x=x-2

the output will be x= 8

Question 25

What will be the output of below code?
x=10
x+=2
print(x)
x-=2
print(x)

Answer 25

For the first print(x) will be 12 and the next one 10. This is because post executing the first print command x now has the value of 12 and the next -= function actually subtracts 2 from 12 thus giving us 10. This is an example of the fact that computer executes sequentially. If you want the subtraction answer as 8 you need to define the variable again.