# Boolean Operators in Python (and, or, not): Mastering Logical Expressions

## Understanding Boolean Operators

Boolean operators in Python help you create conditional statements to control the flow of your program. Python provides three basic Boolean operators: `and`, `or`, and `not`. These operators help you construct sophisticated expressions to evaluate the truth or falsity of different conditions.

### And Operator

The `and` operator returns `True` if both of its operands are true, and `False` otherwise. You can use it to check multiple conditions at once.

Here is a simple example involving the `and` operator:

```age = 25
income = 50000

if age >= 18 and income >= 30000:
print("Eligible for loan")
else:
print("Not eligible for loan")
```

In this example, the condition `age >= 18 and income >= 30000` must be `True` for the program to print `"Eligible for loan"`. If either `age` is less than 18 or `income` is less than 30,000, the condition evaluates to `False`, and the program will print `"Not eligible for loan"`.

### Or Operator

The `or` operator returns `True` as long as at least one of its operands is true. You can use it to specify alternatives in your code.

Here’s an example of how to use the `or` operator:

```student_score = 80
extra_credit = 5

if student_score >= 90 or extra_credit >= 10:
else:
```

In this case, if the `student_score` is 90 or higher, or if the student has completed 10 or more extra credit, the program will print “Student grade: A”. Otherwise, it will print `"Student grade: B"`.

### Not Operator

The `not` operator inverts the truth value of the expression that follows it. It takes only one operand and returns `True` if the operand is `False`, and vice versa. The `not` operator can be used to check if a certain condition is not met.

Here is an example:

```message = "Hello, World!"

if not message.startswith("Hi"):
else:
print("Message starts with 'Hi'")
```

In this example, the program checks whether the `message` does not start with the string `"Hi"`. If it doesn’t, the condition `not message.startswith("Hi")` evaluates to `True`, and the program prints `"Message does not start with 'Hi'"`. If the condition is `False`, the program prints `"Message starts with 'Hi'"`.

## Boolean Values in Python

In Python, Boolean values represent one of two states: True or False. These values are essential for making decisions and controlling the flow of your program. This section covers the basics of Boolean values, the `None` value, and how to convert different data types into Boolean values.

### True and False Values

Boolean values in Python can be represented using the keywords `True` and `False`. They are instances of the `bool` class and can be used with various types of operators such as logical, comparison, and equality operators.

Here’s an example using Boolean values with the logical `and` operator:

```x = True
y = False
result = x and y
print(result)  # Output: False
```

### None Value

In addition to `True` and `False`, Python provides a special value called `None`. `None` is used to represent the absence of a value or a null value. While it’s not a Boolean value, it is considered falsy when used in a Boolean context:

```if None:
print("This won't be printed.")
```

### Converting to Boolean Type

In Python, various data types such as numbers, strings, sets, lists, and tuples can also be converted to Boolean values using the `bool()` function. When converted, these data types will yield a Truthy or Falsy value:

• Numbers: Any non-zero number will be `True`, whereas `0` will be `False`.
• Strings: Non-empty strings will be `True`, and an empty string `''` will be `False`.
• Sets, Lists, and Tuples: Non-empty collections will be `True`, and empty collections will be `False`.

Here are a few examples of converting different data types into Boolean values:

```# Converting numbers
print(bool(10))  # Output: True
print(bool(0))   # Output: False

# Converting strings
print(bool("Hello"))  # Output: True
print(bool(""))       # Output: False

# Converting lists
print(bool([1, 2, 3]))  # Output: True
print(bool([]))         # Output: False
```

π Recommended: How to Check If a Python List is Empty?

## Working with Boolean Expressions

In Python, Boolean operators (`and`, `or`, `not`) allow you to create and manipulate Boolean expressions to control the flow of your code. This section will cover creating Boolean expressions and using them in `if` statements.

### Creating Boolean Expressions

A Boolean expression is a statement that yields a truth value, either `True` or `False`. You can create Boolean expressions by combining conditions using the `and`, `or`, and `not` operators, along with comparison operators such as `==`, `!=`, `>`, `<`, `>=`, and `<=`.

Here are some examples:

```a = 10
b = 20

# Expression with "and" operator
expr1 = a > 5 and b > 30

# Expression with "or" operator
expr2 = a > 5 or b > 15

# Expression with "not" operator
expr3 = not (a == b)
```

In the above code snippet, `expr1` evaluates to `True`, `expr2` evaluates to `True`, and `expr3` evaluates to `True`. You can also create complex expressions by combining multiple operators:

```expr4 = (a > 5 and b < 30) or not (a == b)
```

This expression yields `True`, since both `(a > 5 and b < 30)` and `not (a == b)` evaluate to `True`.

### Using Boolean Expressions in If Statements

Boolean expressions are commonly used in `if` statements to control the execution path of your code. You can use a single expression or combine multiple expressions to check various conditions before executing a particular block of code.

Here’s an example:

```x = 10
y = 20

if x > 5 and y > 30:
print("Both conditions are met.")
elif x > 5 or y > 15:
print("At least one condition is met.")
else:
print("Neither condition is met.")
```

In this example, the `if` statement checks if both conditions are met (`x > 5 and y < 30`); if true, it prints `"Both conditions are met"`. If that expression is false, it checks the `elif` statement (x > 5 or y > 15); if true, it prints `"At least one condition is met."` If both expressions are false, it prints `"Neither condition is met."`

## Logical Operators and Precedence

In Python, there are three main logical operators: `and`, `or`, and `not`. These operators are used to perform logical operations, such as comparing values and testing conditions in your code.

### Operator Precedence

Operator precedence determines the order in which these logical operators are evaluated in a complex expression. Python follows a specific order for logical operators:

1. `not`
2. `and`
3. `or`

Here is an example to illustrate precedence:

```result = True and False or True
```

In this case, `and` has a higher precedence than `or`, so it is evaluated first. The result would be:

```result = (True and False) or True
```

After the `and` operation, it becomes:

```result = False or True
```

Finally, the `result` will be `True` after evaluating the `or` operation.

### Applying Parentheses

You can use parentheses to change the order of evaluation or make your expressions more readable. When using parentheses, operations enclosed within them are evaluated first, regardless of precedence rules.

Let’s modify our previous example:

```result = True and (False or True)
```

Now the `or` operation is performed first, resulting in:

```result = True and True
```

And the final `result` is `True`.

## Truthy and Falsy Values

π‘ Tip: In Python, values can be considered either “truthy” or “falsy” when they are used in a boolean context, such as in an `if` statement or a `while` loop. Truthy values evaluate to `True`, while falsy values evaluate to `False`. Various data types, like numerics, strings, lists, tuples, dictionaries, sets, and other sequences, can have truthy or falsy values.

### Determining Truthy and Falsy Values

When determining the truth value of an object in Python, the following rules apply:

• Numeric types (`int`, `float`, `complex`): Zero values are falsy, while non-zero values are truthy.
• Strings: Empty strings are falsy, whereas non-empty strings are truthy.
• Lists, tuples, dictionaries, sets, and other sequences: Empty sequences are falsy, while non-empty sequences are truthy.

Here are some examples:

```if 42: # truthy (non-zero integer)
pass

if "hello": # truthy (non-empty string)
pass

if [1, 2, 3]: # truthy (non-empty list)
pass

if (None,): # truthy (non-empty tuple)
pass

if {}: # falsy (empty dictionary)
pass
```

### Using `__bool__()` and `__len__()`

Python classes can control their truth value by implementing the `__bool__()` or `__len__()` methods.

π©βπ» Expert Knowledge: If a class defines the `__bool__()` method, it should return a boolean value representing the object’s truth value. If the class does not define `__bool__()`, Python uses the `__len__()` method to determine the truth value: if the length of an object is nonzero, the object is truthy; otherwise, it is falsy.

Here’s an example of a custom class implementing both `__bool__()` and `__len__()`:

```class CustomClass:
def __init__(self, data):
self.data = data

def __bool__(self):
return bool(self.data) # custom truth value based on data

def __len__(self):
return len(self.data) # custom length based on data

custom_obj = CustomClass([1, 2, 3])

if custom_obj: # truthy because custom_obj.data is a non-empty list
pass
```

## Comparisons and Boolean Expressions

In Python, boolean expressions are formed using comparison operators such as greater than, less than, and equality. Understanding these operators can help you write more efficient and logical code. In this section, we will dive into the different comparison operators and how they work with various expressions in Python.

### Combining Comparisons

Some common comparison operators in Python include:

• `>`: Greater than
• `<`: Less than
• `>=`: Greater than or equal to
• `<=`: Less than or equal to
• `==`: Equality
• `!=`: Inequality

To combine multiple comparisons, you can use logical operators like `and`, `or`, and `not`. These operators can be used to create more complex conditions with multiple operands.

Here’s an example:

```x = 5
y = 10
z = 15

if x > y and y < z:
print("All conditions are true")
```

In this example, the `and` operator checks if both conditions are `True`. If so, it prints the message. We can also use the `or` operator, which checks if any one of the conditions is `True`:

```if x > y or y < z:
print("At least one condition is true")
```

### Short-Circuit Evaluation

Python uses short-circuit evaluation for boolean expressions, meaning that it will stop evaluating further expressions as soon as it finds one that determines the final result. This can help improve the efficiency of your code.

For instance, when using the `and` operator, if the first operand is `False`, Python will not evaluate the second operand, because it knows the entire condition will be `False`:

```if False and expensive_function():
# This won't execute because the first operand is False
pass
```

Similarly, when using the `or` operator, if the first operand is `True`, Python will not evaluate the second operand because it knows the entire condition will be `True`:

```if True or expensive_function():
# This will execute because the first operand is True
pass
```

## Common Applications of Boolean Operations

In Python, Boolean operations are an essential part of programming, with and, or, not being the most common operators. They play a crucial role in decision-making processes like determining the execution paths that your program will follow. In this section, we will explore two major applications of Boolean operations – Conditional Statements and While Loops.

### Conditional Statements

Conditional statements in Python, like `if`, `elif`, and `else`, are often used along with Boolean operators to compare values and determine which block of code will be executed. For example:

```x = 5
y = 10

if x > 0 and y > 0:
print("Both x and y are positive")
elif x < 0 or y < 0:
print("Either x or y is negative (or both)")
else:
print("Both x and y are zero or one is positive and the other is negative")
```

Here, the `and` operator checks if both `x` and `y` are positive, while the `or` operator checks if either `x` or `y` is negative. These operations allow your code to make complex decisions based on multiple conditions.

### While Loops

While loops in Python are often paired with Boolean operations to carry out a specific task until a condition is met. The loop continues as long as the test condition remains `True`. For example:

```count = 0

while count < 10:
if count % 2 == 0:
print(f"{count} is an even number")
else:
print(f"{count} is an odd number")
count += 1
```

In this case, the `while` loop iterates through the numbers 0 to 9, using the `not` operator to check if the number is even or odd. The loop stops when the variable `count` reaches 10.

### How do you use ‘and’, ‘or’, ‘not’ in Python boolean expressions?

In Python, `and`, `or`, and `not` are used to combine or modify boolean expressions.

• `and`: Returns `True` if both operands are `True`, otherwise returns `False`.
• `or`: Returns `True` if at least one of the operands is `True`, otherwise returns `False`.
• `not`: Negates the boolean value.

Example:

```a = True
b = False

print(a and b) # False
print(a or b)  # True
print(not a)   # False
```

### How are boolean values assigned in Python?

In Python, boolean values can be assigned using the keywords `True` and `False`. They are both instances of the `bool` type. For example:

```is_true = True
is_false = False
```

### What are the differences between ‘and’, ‘or’, and ‘and-not’ operators in Python?

`and` and `or` are both binary operators that work with two boolean expressions, while `and-not` is not a single operator but a combination of `and` and `not`. Examples:

```a = True
b = False

print(a and b)     # False
print(a or b)      # True
print(a and not b) # True (since 'not b' is True)
```

### How do I use the ‘not equal’ relational operator in Python?

In Python, the `not equal` relational operator is represented by the symbol `!=`. It returns `True` if the two operands are different and `False` if they are equal. Example:

```x = 5
y = 7

print(x != y) # True
```

### What are the common mistakes with Python’s boolean and operator usage?

Common mistakes include misunderstanding operator precedence and mixing `and`, `or`, and `not` without proper grouping using parentheses.

Example:

```a = True
b = False
c = True

print(a and b or c)    # True (because 'and' is evaluated before 'or')
print(a and (b or c))  # False (using parentheses to change precedence)
```

### How is the ‘//’ floor division operator related to boolean operators in Python?

The `//` floor division operator is not directly related to boolean operators. It’s an arithmetic operator that performs division and rounds the result down to the nearest integer. However, you can use it in boolean expressions as part of a condition, like any other operator.

Example:

```x = 9
y = 4

is_divisible = x // y == 2
print(is_divisible) # True
```