Variables in Python

Variables in Python#

A Python variable is like a container that stores data temporarily. You can use this stored data in your code. Variables are essential in any programming language.

  • Variables keep values accessible.

  • Variables give values meaning.

  • Variables make changes easy.

  • Variables have data types.

Variable Declaration#

Python is a dynamically typed language, meaning you create a variable by assigning a value to it. You don’t need to declare its type, and you can change its type later.

Python 3.12.4 (tags/v3.12.4:8e8a4ba, Jun  6 2024, 19:30:16) [MSC v.1940 64 bit (AMD64)] on win32
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>>> # Assign a string value to a variable
>>> device_name = "Router1"
>>> # Assign an integer value to a variable
>>> device_port = 22
>>> # Assign a boolean value to a variable
>>> is_connected = True

You can find out the data type of a variable using the type() function.

>>> ip_addr = "192.168.10.1"
>>> print(type(ip_addr))
<class 'str'>

You can assign values to multiple variables in one line.

>>> vlan_01, vlan_10 = "default", "mgmt"
>>> print(vlan_01, vlan_10)
default mgmt

You can also assign the same value to multiple variables at once.

>>> host = ip_addr = "192.168.10.1"
>>> print(host, ip_addr)
192.168.10.1 192.168.10.1

If you have a list of values, you can extract them into variables.

>>> ip_addr_list = ["10.10.10.10", "172.16.10.10", "192.168.10.10"]
>>> ip_addr1, ip_addr2, ip_addr3 = ip_addr_list
>>> print(ip_addr1)
10.10.10.10
>>> print(ip_addr2)
172.16.10.10
>>> print(ip_addr3)
192.168.10.10

Assignment Statements#

An operator is a symbol that performs operations on values. The assignment operator = assigns the value on the right to the variable on the left.

>>> hostName = "R-01"
>>> print(hostName)
R-01

You can use single or double quotes for string variables.

>>> hostName = "R-01"
>>> print(hostName)
R-01
>>> hostName = 'R-01'
>>> print(hostName)
R-01

Variable Naming Convention#

Variable names can be long or short, but there are some rules:

  • Must start with a letter or underscore.

  • Cannot start with a number.

  • Can only contain letters, numbers, and underscores.

  • Keywords cannot be used as variable names.

  • Variable names are case-sensitive.

>>> # Camel Case - Each word, except the first, starts with a capital letter.
>>> myVariableName = "Alex"
>>> # Pascal Case - Each word starts with a capital letter.
>>> MyVariableName = "Alex"
>>> # Snake Case - Words are separated by underscores.
>>> my_variable_name = "Alex"

Use all-caps for constants or configuration values that shouldn’t change.

>>> # Define a constant value using all-caps naming convention
>>> MAX_DEVICES = 100

Using meaningful variable names like device_name, device_ip, device_username, and device_password makes your code more readable and easier to understand.

Use Descriptive Names#

Choose variable names that are descriptive and convey their purpose. Avoid generic names like temp or data. Instead, use names like ip_address or server_name to make your code more readable.

Use Underscores#

For multi-word variable names, use underscores to separate words, following the snake_case convention. For example, device_name is more readable than deviceName.

Avoid Reserved Words#

Be careful not to use Python’s reserved words as variable names. For example, naming a variable print or for can lead to unexpected behavior.

Consistency#

Maintain consistency in your variable naming. If you use ip_address in one part of your code, don’t switch to ip_addr elsewhere. Consistency simplifies code comprehension.

Python Naming Conventions#

Following naming conventions is essential for writing clean and maintainable Python code. Here are some common conventions:

  • snake_case_lower for variables and functions.

  • PascalCase for class names.

  • SNAKE_CASE_UPPER for constants.

Let’s dive deeper into these conventions:

Variable Names#

  • Start variable names with a lowercase letter or underscore.

  • Use clear and descriptive names that convey the variable’s purpose.

  • For multi-word variable names, use underscores for separation (e.g., user_id).

Function Names#

  • Begin function names with a lowercase letter or underscore.

  • Use descriptive names that hint at the function’s action or purpose.

  • For multi-word function names, use underscores (e.g., calculate_speed).

Class Names#

  • Start class names with an uppercase letter.

  • Use CamelCase, where each word in the name begins with an uppercase letter and has no underscores (e.g., NetworkDevice).

Constant Names#

  • Constant variables should be in uppercase with words separated by underscores (e.g., MAX_CONNECTIONS).

By following these naming conventions, you’ll make your Python code more accessible and comprehensible to yourself and others who collaborate on your projects.

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