4.1. Boolean expressions

A boolean expression is an expression that is either true or false. The following examples use the operator ==, which compares two operands and produces True if they are equal and False otherwise:

print(5 == 5) print(5 == 6)

True and False are special values that belong to the class bool; they are not strings:

print(type(True)) print(type(False))

The == operator is one of the comparison operators; the others are:

x != y               # x is not equal to y
x > y                # x is greater than y
x < y                # x is less than y
x >= y               # x is greater than or equal to y
x <= y               # x is less than or equal to y
x is y               # x is the same as y
x is not y           # x is not the same as y

Although these operations are probably familiar to you, the Python symbols are different from the mathematical symbols for the same operations. A common error is to use a single equal sign (=) instead of a double equal sign (==). Remember that = is an assignment operator and == is a comparison operator. There is no such thing as =< or =>.

Q-3: Which of the following is a Boolean expression? Select all that apply.

• True
• True and False are both Boolean literals.
• 3 == 4
• The comparison between two numbers via == results in either True or False (in this case False), both Boolean values.
• 3 + 4
• 3 + 4 evaluates to 7, which is a number, not a Boolean value.
• 3 + 4 == 7
• 3 + 4 evaluates to 7. 7 == 7 then evaluates to True, which is a Boolean value.
• "False"
• With the double quotes surrounding it, False is interpreted as a string, not a Boolean value. If the quotes had not been included, False alone is in fact a Boolean value.

Q-4: Which of the following comparison operators is used to check if x and y are the same object?

• x = y
• Try again. This reassigns the value of y to x.
• x != y
• Try again. This means that x is not equal to y.
• x == y
• Try again. This means that x and y have the same value, but it does not mean they are the same object.
• x is y
• This means that x and y are the same object, not just the same value.
• x is not y
• Try again. This means that x and y are not the same object. This can be true if x and y have the same value, but are stored in different objects.

Q-5: What operator makes 783 ___ 206 true? Select all that apply.

• >
• 783 > 206 is True.
• <=
• Try again. 783 <= 206 is False.
• True
• Try again.
• !=
• Correct! 783 != 206 is True.
• is not
• Correct! 783 is not 206 is True.

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