Python Variables

Python Variables at a Glance

A variable gives a value a meaningful name so a script can store it once, reuse it, and replace it when newer data becomes available.

1. Strings

A variable is a name for a value. Use the equal sign (=) to assign the value on the right to the name on the left.

For example, a script may need the same device name in several messages. Store it once instead of typing it again and again:

>>> device_name = "R1"
>>> device_name
'R1'

Pass the variable to print() whenever the device name is needed:

>>> device_name = "R1"
>>> print("Checking", device_name)
Checking R1

Every use of device_name now reads the stored text. The name also explains what the value means.

2. Numbers

Variables can store numbers such as retry limits, VLAN IDs, and interface counters. Numbers do not use quotes:

>>> failed_checks = 2
>>> total_checks = 10
>>> print(failed_checks)
2
>>> print(total_checks)
10

Once the values are assigned, you can use their variable names in expressions:

>>> passed_checks = total_checks - failed_checks
>>> print(passed_checks)
8

3. Update a Variable

You can assign a new value to an existing variable. Python uses the most recent value:

>>> interface_state = "down"
>>> interface_state = "up"
>>> print(interface_state)
up

4. Copy a Value

You can use the current value of one variable while assigning another:

>>> primary_ip = "192.0.2.10"
>>> test_target = primary_ip
>>> print(test_target)
192.0.2.10

If primary_ip later changes, test_target still contains the text copied during its assignment:

>>> primary_ip = "192.0.2.10"
>>> test_target = primary_ip
>>> primary_ip = "192.0.2.11"
>>> print(test_target)
192.0.2.10

Python did not create a permanent link between the two names. Changing primary_ip does not automatically update test_target.

5. Store Function Results

A variable can store the result returned by a function. The input() function waits for the user to enter text:

>>> hostname = input("Enter hostname of device: ")
Enter hostname of device: R1
>>> print(hostname)
R1

After the user enters R1 and presses Enter, the returned text is assigned to hostname. The program can then reuse that value in connection messages, logs, or later device operations.

6. Variable Names

Names such as x, y, and z are short, but they do not explain what the data represents. A name such as hostname immediately provides context. At the other extreme, hostname_from_user_input_function is unnecessarily long and awkward to reuse.

Real-world example: describe a connection check

device_name = "R1"
device_ip = "192.0.2.10"
retry_count = 3

print(f"Checking {device_name} at {device_ip}; retries: {retry_count}")

The output states which device will be checked, which address will be used, and how many retries are allowed. The variable names make the code understandable without extra comments.

7. Conclusion

In this lesson, you learned how Python variables make values reusable:

• Assignment gives a variable name a value.
• Variables can store strings, numbers, function results, and many other data types.
• Reassigning a variable makes its name refer to a new value.
• One variable can be assigned from the value referenced by another variable.
• Short, meaningful names make code easier to read and maintain.