Variables
What is a variable?
In programming a variable is often referred to as named storage location that stores a data or value. The data or value stored in a variable may change through out the program execution.
Variables data type
A variable data type is a refers to the type of value or data a variable is storing.
Variables data type in python are derived from the value they store, because Python is a dynamically-typed, meaning the variable data type is subject to change with respect to change of its value type.
Constants
A constant is a value or data which can be used but can’t be modified during the program execution. It stores a fixed value unlike a variable whose value can be changed.
It’s value is meant to not be modified once assigned.
Defining a constant
When defining a constant, all the characters of the constant name should be in upper case.
PI = 3.14 MONTHS = 12
Variable - Naming conventions:
Variable naming conventions are a set of guidelines that helps in choosing a descriptive and meaningful names for variables. Which helps make the code more readable and maintainable if consistently adhered to.
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variable name should be descriptive and meaningful
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Do not use abriviations unless widely used (e.g., URL)
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Use lowercase letters, underscores, and numbers (e.g., my_variable)
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Avoid using special characters like $ and _ as the first character
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if a variable name contains more than one word then join them using use underscore _ (e.g., my_seond_variable)
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Constants are written in all uppercase (e.g., PI)
Example
# acceptable variable name department = "Computer Science"
# not acceptable SyntaxError: invalid decimal literal 3department = " "
Things to know:
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A variable maybe referenced by several different identifiers.
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Assigning a value to a variable using one of identifiers will change the value that can be accessed through other identifiers.
Scope of a variable
Scope of variable determines its accessibility within a program, in simple terms, it determines from where within your code you can use a variable.
Global-variable
Global variables have a global scope therefore they are accessible everywhere within your code.
# Global variablename = "Alice"
def greet(): # Accessing the global variable inside the function print("Hello, " + name + "!")
def change_name(new_name): global name # Declaring that we want to modify the global variable name = new_name
# Call the functionsgreet() # Output: Hello, Alice!
change_name("Bob")greet() # Output: Hello, Bob!
Local-variable
Local variables have a local scope therefore they are only accessible within a function or block scope.
def greet(): # Local variable name = "Alice" print("Hello, " + name + "!")
def change_name(): # This 'name' variable is local to this function and different from the one in greet() name = "Bob" print("Inside change_name, name is: " + name)
# Call the functionsgreet() # Output: Hello, Alice!change_name() # Output: Inside change_name, name is: Bob
# Trying to access the local variable outside the function will cause an error# print(name) # Uncommenting this line will result in a NameError