Variables, Data Types & Basic Operations

Creating a variable

The last lesson showed one variable without explaining the syntax. Here's the full picture: writing name = value creates a variable — a label pointing at a value — that the rest of the script can use by name.

device_name = "SW1"
device_ip = "10.10.10.1"
ssh_port = 22
is_reachable = True

Each line follows the same pattern: a name on the left, an =, and a value on the right. Nothing runs yet — this just stores four values under four names, the same way you'd note down four facts about a switch before doing anything with them.

The four basic data types

Every value in the example above belongs to one of Python's basic types:

• String (str) — text, always wrapped in quotes: "SW1", "10.10.10.1". Hostnames, IP addresses, and platform names are almost always strings, even when they look numeric.
• Integer (int) — a whole number, no quotes: 22, 48. A port number or a VLAN ID is typically an integer.
• Float — a number with a decimal point: 98.5, 0.75. Less common in day-to-day device facts, but shows up in things like CPU utilization percentages or link latency in milliseconds.
• Boolean (bool) — exactly True or False, capitalized, no quotes. is_reachable = True is a boolean — a direct yes/no fact about the device.

Why the type actually matters

Here's a mistake almost everyone makes once: comparing a value to the wrong type.

config_port = "22"    # read from a config file as text
ssh_port = 22         # a plain integer

print(config_port == ssh_port)   # False!

This isn't a Python quirk to memorize and move on from — it's exactly the kind of bug that shows up in real automation, because config files, command output, and user input often hand you numbers as text. Comparing a port number read from a file against a plain integer without converting one of them first is a genuinely common source of "why did this check silently fail?" moments.

Basic operators

A few operators come up constantly in automation scripts:

• Arithmetic: +, -, *, / — mostly on numbers. vlan_count + 1.
• Comparison: == (equal), != (not equal), <, > — these produce a boolean (True/False), and are the backbone of every condition you'll write in the next lesson.
• String concatenation: joining text together. "SW" + "1" produces "SW1". Mixing a string and a number directly with + (like "Port: " + 22) raises an error — you'd need str(22) first, or (the more common, more readable approach) an f-string like f"Port: {22}", which you already saw in Lesson 1.

Changing a value

A variable isn't locked in after its first assignment — reassigning it just points the name at a new value:

device_ip = "10.10.10.1"
print(device_ip)   # 10.10.10.1

device_ip = "10.10.10.2"   # same variable, new value
print(device_ip)   # 10.10.10.2

Why this matters for automation

None of this is abstract housekeeping — it's exactly what makes a script able to work with changing device information instead of numbers and names baked directly into the code. A script that hardcodes "10.10.10.1" everywhere it needs a switch's address only ever works for that one switch. A script that reads each switch's IP into a variable — the same device_ip name, filled with a different value each time through a loop — works for one switch or five hundred, without changing a line of logic. That's the whole reason variables matter here: they're what makes "the same script, different devices" possible.