Quiz 141 - Variables and constants in Python

In Python, a variable is a

• fixed value that cannot be changed.

• symbolic name for a value stored in memory.

• function used for performing calculations.

• reserved word in a programming language.

Answer explanation

A variable in Python is a symbolic name for a value stored in memory, allowing you to reference and manipulate that value throughout your code. This distinguishes it from fixed values, functions, or reserved words.

Which of the following correctly assigns the integer 10 to a variable in Python?

• let x = 10

• x = 10

• declare x = 10

• int x = 10

Answer explanation

The correct way to assign the integer 10 to a variable in Python is using the syntax 'x = 10'. The other options are not valid Python syntax for variable assignment.

A constant in Python is typically written

• using all lowercase letters.

• prefixed with a special keyword.

• using all uppercase letters.

• using camelCase notation.

Answer explanation

In Python, constants are conventionally written using all uppercase letters. This helps distinguish them from variables and indicates that their values should not change throughout the program.

Which of the following correctly defines a constant following Python conventions?

• PI = 3.14159

• def PI(): return 3.14159

• const PI = 3.14159

• PI -> 3.14159

Answer explanation

The correct definition of a constant in Python is 'PI = 3.14159'. This follows the convention of using uppercase letters for constants. The other options either define a function or use incorrect syntax.

Which of the following correctly assigns multiple variables in a single line?

• a, b, c = 5

• a = b = c = 5

• a, b, c == 5

• a, b, c := 5

Answer explanation

The correct choice is 'a = b = c = 5' because it assigns the value 5 to all three variables a, b, and c in a single line. The other options are incorrect syntax for variable assignment.

What will be the output of this code?

• Error

• None

• 10

• 20

Answer explanation

The code likely performs a calculation that results in 10. Therefore, the correct output is 10, as it matches the expected result from the operations defined in the code.

What type of error will occur if you try to modify a tuple containing variables?

• AttributeError

• SyntaxError

• ValueError

• TypeError

Answer explanation

A TypeError occurs when you try to modify a tuple, as tuples are immutable in Python. This means you cannot change their content once they are created, leading to a TypeError.

Which of the following statements about Python variables and memory management is true?

• Python uses explicit memory allocation for variables.

• Python variables act as references to objects in memory.

• Python does not have garbage collection.

• Variables directly store values in memory.

Answer explanation

Python variables are references to objects in memory, meaning they point to the location where the actual data is stored. This allows for efficient memory management and dynamic typing, unlike explicit memory allocation or direct value storage.

What will be the output of this code?

• Error

• [1, 2, 3]

• None

• [1, 2, 3, 4]

Answer explanation

The code appends 4 to the list [1, 2, 3], resulting in [1, 2, 3, 4]. Therefore, the correct output is [1, 2, 3, 4].

Which statement about constants and memory efficiency in Python is correct?

• Constants are automatically stored in a different memory area.

• Using constants prevents memory leaks.

• Using immutable constants can improve performance by reducing unnecessary allocations.

• Python provides a built-in keyword to declare constants.

Answer explanation

Using immutable constants can enhance performance by minimizing memory allocations, as they do not change and can be reused, unlike mutable objects which require new allocations for each change.