python variables by KK FUNDA
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–> In Python, variables are used to store data values.
1. What is a Variable?
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A variable in Python is simply a name that refers to a value. You can think of it as a label that points to a specific value in memory.
2. Variable Assignment
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In Python, you create a variable by assigning it a value using the `=` operator:
Example:
x = 5 # Here, `x` is the variable and 5 is the value assigned to it.
name = “Alice” # `name` is a variable holding the string “Alice”.
3. Variable Naming Rules
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Variable names must follow these rules:
– Start with a letter (a-z, A-Z) or an underscore (`_`).
– The rest of the name can contain letters, digits (0-9), or underscores.
– Python is case-sensitive, so `myVar`, `myvar`, and `MYVAR` are all different variables.
– Avoid using Python keywords (reserved words) such as `if`, `else`, `for`, `while`, etc.
Example:
variable_1 = 10 # Valid
1variable = 10 # Invalid (starts with a number)
4. Data Types of Variables
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Variables in Python can hold values of different data types. Here are some common types:
– Integer (`int`): Represents whole numbers.
age = 30
– Floating-point (`float`): Represents decimal numbers.
price = 19.99
– String (`str`): Represents a sequence of characters enclosed in quotes.
name = “Alice”
– Boolean (`bool`): Represents either `True` or `False`.
is_active = True
– List (`list`): An ordered collection of items, which can be of different data types.
numbers = [1, 2, 3, 4]
– Tuple (`tuple`): An ordered, immutable collection of items.
coordinates = (10, 20)
– Dictionary (`dict`): A collection of key-value pairs.
student = {“name”: “Alice”, “age”: 25}
– Set (`set`): A collection of unique items.
fruits = {“apple”, “banana”, “cherry”}
– NoneType (`None`): Represents the absence of a value.
result = None
5. Dynamic Typing
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Python is a dynamically-typed language, meaning that you don’t need to declare the data type of a variable explicitly. The type of the variable is inferred from the value assigned to it.
Example:
x = 10 # `x` is an integer
y = “Hello” # Now `y` is a string
6. Multiple Assignments
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Python allows you to assign values to multiple variables in a single line.
Example:
a, b, c = 1, 2.5, “Hello” # `a` gets 1, `b` gets 2.5, `c` gets “Hello”
7. Constant Variables
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Python does not have a built-in constant type, but by convention, variables written in all uppercase letters are considered constants (they shouldn’t be changed).
Example:
PI = 3.14159 # This is considered a constant.
8. Type Conversion
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You can explicitly convert variables from one type to another using functions like `int()`, `float()`, `str()`, etc.
Example:
x = “100” # `x` is a string
x = int(x) # Now `x` is an integer
9. Global and Local Variables or scope of variable
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– Local Variables: These are defined inside a function and are only accessible within that function.
– Global Variables: These are defined outside any function and can be accessed anywhere in the program.
Example:
x = 10 # Global variable
def my_function():
y = 5 # Local variable
print(x + y) # Accessing global variable `x` inside the function
my_function() # Output: 15
10. Variables in Expressions
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Variables can be used in expressions to perform operations.
Example:
a = 5
b = 10
sum_ab = a + b # sum_ab will hold the value 15
11. Deleting Variables
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You can delete a variable using the `del` keyword. This removes the variable from memory.
Example:
x = 10
del x # `x` no longer exists after this statement
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Summary:
– Variables store values in Python.
– Python is dynamically typed, so you don’t need to specify the type when assigning a value.
– Variable names must follow certain naming rules.
– Python has several built-in data types, such as `int`, `float`, `str`, `list`, and more.
– You can use multiple assignments and type conversion in Python.
– Variables have local and global scopes, and you can use the `global` keyword to modify global variables inside functions.
Understanding how variables work is fundamental to writing effective Python code, as they are the building blocks for storing and manipulating data.
