Python Variables

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Python variables are symbolic names that represent stored values in a program.

• serve as placeholders to store and manage data
• can be numbers, strings, lists, etc.
• don’t need to explicitly declare a variable’s data type
  • it is dynamically inferred based on the assigned value
• variable names are case sensitive

Creating a Variable

• Python variables are not declared
  • they are created as soon as they are assigned a value
• do not have a set type
  • can change their type
• variables are case sensitive

x = 42
x = "Cisco South Router"

Variable Name Rules

1. Variable names can only contain letters, numbers, or an underscore.
2. Variable names must start with either a letter or underscore. 
3. Variable names cannot start with a number.
4. Variable names cannot contain special characters.
5. Variable names cannot be a Python keyword (opens new tab).

Variables with Multiple Names

• use Camel case for variable names

chicagoFirewall = "192.168.26.254"
losAngelesFirewall = "192.168.28.254"

• can also use Pascal case or snake case

Multiple Variables

• can assign values to multiple values in a single line
  • e.g., x, y, z = "router", "switch", "firewall"
• can assign the same value to multiple variables in a single line
  • e.g., switch1 = switch2 = switch3 = "Juniper"

Unpacking Collections

Unpacking involves extracting elements from iterable objects like lists or tuples and assigning them to individual variables.

ip_addresses = ["172.20.200.10", "172.20.200.11", "172.20.200.12"]
ip1, ip2, ip3 = ip_addresses

Output Variables

• output variables with print() function
  • can output multiple variables: print(a, b, c)
  • concatenate them with + : print(a + b + c)
    • using different typed variables will result in error

Variable Scope

Variable scope in Python refers to the region of code where a variable can be accessed.

• Local scope is within a specific function
• Global scope extends throughout the entire program
• Variables defined within a function (local) are not accessible outside

global Keyword

• can create a global variable inside a function with global
  • can also be used to change a global variable within a function

def routerAddress():
    global ip1
    ip1 = "10.10.100.250"
routerAddress()
print("The router address is " + ip1)