Python Variables

print(x)

This will output:

5

Variables in Python are dynamically typed, meaning you don’t have to specify the type of data the variable will hold. Python will automatically determine the type based on the value you assign to the variable.

For example, if you assign a string to a variable, the variable will be of type string:

name = "John"

If you assign a number to a variable, the variable will be of type int or float depending on the type of number you assign:

age = 25
height = 1.75

You can also change the value of a variable at any time by simply assigning a new value to it:

x = 5
print(x)  # Output: 5

x = 10
print(x)  # Output: 10

Object References:

In Python, all values are objects, and variables are simply references to those objects. When you create a variable and assign it a value, you’re actually creating a reference to an object in memory.

For example, when you create a variable x and assign it the value 5, Python creates an integer object in memory with the value 5, and then creates a reference to that object with the name x. This means that x is not the actual value 5, but a reference to the object in memory that contains the value 5.

This is important to understand because when you assign one variable to another, you’re actually copying the reference, not the object itself. For example:

x = 5
y = x

In this code, y is not a copy of the object that x refers to, but rather a new reference to the same object. This means that any changes you make to the object through either x or y will be reflected in both variables.

x = 5
y = x
y = y + 1

print(x)  # Output: 5
print(y)  # Output: 6

In this example, we first create x and assign it the value 5. Then we create y and assign it the value of x. When we add 1 to y, we’re actually creating a new integer object with the value 6, and then creating a reference to that object with the name y. This means that x is still referencing the original integer object with the value 5, and y is referencing a new integer object with the value 6.

It’s important to keep this behavior in mind when working with variables and objects in Python, as it can lead to unexpected results if you’re not aware of it.

Object Identity:

In Python, every object has a unique identity, which is a value that’s guaranteed to be unique and constant for that object during its lifetime. You can think of an object’s identity as its memory address – it’s the location in memory where the object is stored.

In Python, you can use the id() function to get the identity of an object. For example:

x = 5
print(id(x))

This will output a unique integer value that represents the identity of the integer object that x references.

You can also use the is operator to check if two variables reference the same object. For example:

x = 5
y = x

print(x is y)  # Output: True

In this example, x and y both reference the same integer object with the value 5, so x is y evaluates to True.

On the other hand, if you create two variables with the same value, they will reference different objects with different identities:

x = 5
y = 5

print(x is y)  # Output: True

In this example, x and y both have the same value of 5, but they reference different integer objects with different identities, so x is y evaluates to False.

It’s important to understand object identity in Python, as it can affect how variables and objects behave in your code. For example, if you’re checking for equality between two objects, you should use the == operator to compare their values, rather than the is operator to compare their identities.

Variable Names:

In Python, variable names are case-sensitive and can contain letters, numbers, and underscores (_), but cannot start with a number. It’s generally recommended to use descriptive names for your variables that make it clear what they represent or store.

Here are some rules and best practices for naming variables in Python:

• Variable names should be lowercase, with words separated by underscores, e.g. my_variable_name.
• Avoid using names that are too short or too long – aim for something descriptive but not overly verbose.
• Don’t use reserved words as variable names, such as if, else, for, while, class, def, import, etc.
• Use camelCase or PascalCase only when following a specific convention, such as naming class names.
• Try to use meaningful names that reflect the purpose of the variable. For example, name is a better variable name than n.
• Use plural variable names when referring to collections, such as lists or dictionaries. For example, students is a better variable name than student_list.
• Don’t use single-letter variable names, except for loop counters or other situations where the variable’s purpose is obvious.
• Be consistent in your naming conventions throughout your code.

It’s important to choose good variable names to make your code more readable and understandable to other developers who may read your code.

Multiple Assignment:

In Python, you can assign values to multiple variables in a single line of code using multiple assignment (also known as tuple unpacking). Multiple assignment allows you to assign multiple values to multiple variables in a single statement, using tuples or lists.

For example:

x, y, z = 1, 2, 3

my_list = [1, 2, 3]
x, y, z = my_list

x, y, *z = [1, 2, 3, 4, 5]
print(x)  # Output: 1
print(y)  # Output: 2
print(z)  # Output: [3, 4, 5]

x = 5
y = 3.14
z = "hello"
a = True
b = [1, 2, 3]
c = (4, 5, 6)
d = {"name": "John", "age": 30}

print(type(x))  # Output: <class 'int'>
print(type(y))  # Output: <class 'float'>
print(type(z))  # Output: <class 'str'>
print(type(a))  # Output: <class 'bool'>
print(type(b))  # Output: <class 'list'>
print(type(c))  # Output: <class 'tuple'>
print(type(d))  # Output: <class 'dict'>

x = 5
print(type(x))  # Output: <class 'int'>

x = 3.14
print(type(x))  # Output: <class 'float'>

x = "hello"
print(type(x))  # Output: <class 'str'>

import sys

print(sys.maxsize)

x = 5
print(x)

x = 5
y = 10
z = "hello"

print(x, y, z)
x = 5
y = 10
z = "hello"

print(x, y, z)

x = 5
y = 10
z = "hello"

print("x is {}, y is {}, z is {}".format(x, y, z))