Exercise: Variables

Questions for: Variables

Which of the following statements about Python variables is true?
A:
Python is a statically typed language.
B:
A variable must be declared with a type before it can be used.
C:
Python allows multiple assignments in a single line.
D:
A variable's scope is determined by the type of data it holds.
Answer: C
Python is a dynamically typed language. In Python, a variable's type is inferred from the value it's assigned. A variable's scope is determined by where it's defined in the code.

For example:

a, b, c = 1, 2, 3

This statement assigns the values 1, 2, and 3 to the variables a, b, and c, respectively.

You can also assign the same value to multiple variables in one line:

a = b = c = "Orange"

This statement assigns the value "Orange" to the variables a, b, and c.

If you have a collection of values in a list, tuple, etc. Python allows you to extract the values into variables. This is called unpacking. For example:

fruits = ["apple", "banana", "cherry"]
a, b, c = fruits

This statement extracts the values "apple", "banana", and "cherry" from the list fruits and assigns them to the variables a, b, and c, respectively.

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What is the output of the following code: 
my_string = "hello"
my_string[1] = "a"
print(my_string)
A:
hello
B:
hallo
C:
An error is raised
D:
None of the above
Answer: C

In Python, strings are immutable, which means their individual characters cannot be modified once they're created.

Attempting to change a character of a string using the index operator [ ] results in a TypeError.

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What is the output of the following code: 
my_list = [1, 2, 3]
my_list[1] = 4
print(my_list)
A:
[1, 2, 3]
B:
[1, 4, 3]
C:
[4, 2, 3]
D:
An error is raised
Answer: B

In this code, the variable my_list is initially assigned a list containing the values 1, 2, and 3.

The second element of the list (which has an index of 1) is then changed to 4 using the assignment operator =.

When my_list is printed to the console, it shows the modified list [1, 4, 3].

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Which of the following is a valid way to check if a value is in a list called my_list?
A:
if my_value in my_list
B:
if my_list[ my_value ]
C:
if my_value in my_list == True
D:
All of the above
Answer: A
In Python, the in and not in operators can be used to check if a value is or is not in a list, respectively.
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What is the value of y after executing the following code: 
x = [1, 2, 3]
y = x
x = [4, 5, 6]
print(y)
A:
[4, 5, 6]
B:
[1, 2, 3]
C:
[1, 2, 3, 4, 5, 6]
D:
An error is raised
Answer: B

In this code, the variable x is initially assigned a list containing the values 1, 2, and 3.

The variable y is then assigned the same list that x holds a reference to.

However, when x is reassigned a new list containing the values 4, 5, and 6, y still holds a reference to the original list [1, 2, 3].

So when y is printed to the console, it prints [1, 2, 3].

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