is: Returns True if both variables point to the exact same object in memory.

In Python, the is identity operator is used for one primary purpose: to check if two variables refer to the exact same object in memory.

1. Object Identity vs. Value Equality

This is the most critical concept to understand. The is operator checks for identity, while the == operator checks for equality.

• == (Equality): Returns True if the values of the objects are the same.

• is (Identity): Returns True only if both variables point to the exact same object in memory.

You can increase the power of your code by using is to understand how Python manages memory and to perform highly efficient checks against singleton objects like None.

Example Code:

Python

# --- Comparing Lists ---

list_a = [1, 2, 3]

list_b = [1, 2, 3]

list_c = list_a

print(f"list_a == list_b: {list_a == list_b}")

# Output: True (Their contents are equal)

print(f"list_a is list_b: {list_a is list_b}")

# Output: False (They are two separate objects in memory that happen to hold the same values)

print(f"list_a is list_c: {list_a is list_c}")

# Output: True (list_c is just another name for the exact same object as list_a)

2. The Powerful Use Case: Checking for None

The most common and powerful use of the is operator is to check if a variable is None. Because there is only one None object in Python, you should always use is for this comparison. It's faster and the universally accepted convention.

Example Code:

Python

my_variable = None

# The powerful and correct way to check for None

if my_variable is None:

    print("The variable has no value.")

# This also works, but 'is' is preferred

if my_variable == None:

    print("This also works, but 'is' is the standard.")

Applying it to Your Vector2D Class

You can use the is operator to check if two variables are pointing to the exact same Vector2D instance, which is different from checking if they have the same x and y values.

Example with your Canvas code:

Python

# This code references the Vector2D class in your Canvas

v1 = Vector2D(10, 20)

v2 = Vector2D(10, 20) # A different object with the same values

v3 = v1              # The same object as v1

print(f"v1 == v2: {v1 == v2}")

# Output: False (By default, custom objects are only equal if they are the same object)

print(f"v1 is v2: {v1 is v2}")

# Output: False (They are different objects in memory)

print(f"v1 is v3: {v1 is v3}")

# Output: True (v3 is a reference to the exact same object as v1)

is not: Returns True if both variables point to different objects in memory.

In Python, the is not operator is used for one primary purpose: to check if two variables refer to different objects in memory.

1. Object Identity vs. Value Inequality

This is the most important concept to understand when using is not. It checks for the opposite of the is operator.

• != (Value Inequality): Returns True if the values of the objects are different.

• is not (Identity): Returns True only if both variables point to different objects in memory, even if their values are the same.

You can increase the power of your code by using is not to perform highly efficient checks against singleton objects like None and to understand how Python manages memory.

Example Code:

Python

# --- Comparing Lists ---

list_a = [1, 2, 3]

list_b = [1, 2, 3]

list_c = list_a

print(f"list_a != list_b: {list_a != list_b}")

# Output: False (Their contents are equal, so they are not unequal)

print(f"list_a is not list_b: {list_a is not list_b}")

# Output: True (They are two separate objects in memory)

print(f"list_a is not list_c: {list_a is not list_c}")

# Output: False (list_c is just another name for the exact same object as list_a)

2. The Powerful Use Case: Checking for None

The most common and powerful use of the is not operator is to check if a variable has a value and is not None. Because there is only one None object in Python, you should always use is not for this comparison. It's faster and the universally accepted convention.

Example Code:

Python

def get_user(user_id):

    users = {1: "Alice", 2: "Bob"}

    return users.get(user_id) # .get() returns None if the key is not found

user = get_user(3) # This will be None

# The powerful and correct way to check if a value was found

if user is not None:

    print(f"Found user: {user}")

else:

    print("User not found.")

# Output: User not found.

Applying it to Your Vector2D Class

You can use the is not operator to check if two variables are pointing to different Vector2D instances, which is distinct from checking if they have different x and y values.

Example with your Canvas code:

Python

# This code references the Vector2D class in your Canvas

v1 = Vector2D(10, 20)

v2 = Vector2D(10, 20) # A different object with the same values

v3 = v1              # The same object as v1

print(f"v1 is not v2: {v1 is not v2}")

# Output: True (They are different objects in memory)

print(f"v1 is not v3: {v1 is not v3}")

# Output: False (v3 is a reference to the exact same object as v1)