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Variables

A variable is a named container that holds a value. In Python, you don't declare a variable in advance — it is created the moment you assign a value to it using =.

Creating Variables

x = 42
switchName = "Cisco2960_south"

print(x)           # 42
print(switchName)  # Cisco2960_south

Variables Have No Fixed Type

Unlike languages like Java or C, Python variables don't have a locked-in type. The same variable can hold an integer one moment and a string the next: 

x = 42              # x is an int
x = "Cisco2960"     # x is now a str — this is valid in Python

Case Sensitivity

Variable names are case-sensitive, meaning switchName, SWITCHNAME, and switchname are three completely different variables. Best practice is to never rely on case differences to distinguish variables — use descriptive names instead: 

# Bad practice — confusing
switchname = "Cisco2960_east"
SWITCHNAME = "Cisco2960_west"

# Good practice — clear and distinct names
switchname_east = "Cisco2960_east"
switchname_west = "Cisco2960_west"

Variable Naming Rules

  • Can contain letters, numbers, and underscores (_)
  • Cannot start with a number (2device is invalid, device2 is fine)
  • Cannot use Python reserved keywords (like if, for, while, def)
  • Convention: use snake_case for variable names (e.g., device_name, ip_address)

Multiple Assignment

Python lets you assign multiple variables in a single line: 

# Assign different values to multiple variables at once
x, y, z = "router", "switch", "firewall"
print(x)  # router
print(y)  # switch
print(z)  # firewall

# Assign the same value to multiple variables
switch1 = switch2 = switch3 = "Juniper"

⚠️ When assigning multiple values, the number of variables must match the number of values exactly, or Python will raise a ValueError.

Unpacking a Collection

If you have a list or tuple, you can unpack its values directly into individual variables in one line: 

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

print(ip1)  # 172.20.200.10
print(ip2)  # 172.20.200.11
print(ip3)  # 172.20.200.12

Printing Variables

The print() function is the most common way to display output: 

ip1 = "10.100.200.30"
ip2 = "10.100.200.40"

# Comma-separated — print() adds a space between items automatically
print(ip1, ip2)

# Using + to concatenate strings (all items must be strings)
print("Primary IP: " + ip1)

# f-string (most flexible — can mix variables and text cleanly)
print(f"Primary: {ip1}, Secondary: {ip2}")