Get Started with Python - Part 2
This is the second part of the Jump In guide introducing core Python concepts in a hands-on way, using Jupyter notebooks as the primary environment. This page will cover variables and built-in functions. Be sure to check out the accompanying notebook for more experience.
NOTE: By design, Python does not return anything when a variable is assigned. So example cells here, where only variable assignment happens, will run without generating output. The variable is still saved in the runtime and can be accessed in following cells once it is set.
Effective programming is built around reusability. Creating automated, reproducible code starts with variables and functions.
Variables
Variable assignment stores data in a named container. In Python, use = to assign values: x = 5. Variables are case-sensitive and can store numbers, strings, lists, and other datatypes. Variables in Python are mutable meaning the value can be modified.
The cells below set a variable x, print it, update it, and print it again.
Naming Variables
Variables names should be short and meaningful. Long names take time to type and can make code dense. Uninformative names can get confusing or accidentally overwritten.
Python rules for variable names include:
- Letters, numbers, and underscores (
_) only - Must start with a letter or underscore
- Snake case is preferred (e.g., my_var)
- No spaces, dashes, or dots
- Can not be reserved Python word (e.g.,
if,return)
See the table below for more examples.
| Example | Valid? | Reason |
|---|---|---|
| age | ✅ Yes | Starts with a letter, letters only |
| user_name | ✅ Yes | Letters + underscore are allowed |
| temperature2 | ✅ Yes | Digits allowed, but not at start |
| _hidden | ✅ Yes | Leading underscore allowed (often used for “private” values) |
| MAX_VALUE | ✅ Yes | Uppercase is allowed, often used for constants |
| 2nd_value | ❌ No | Cannot start with a digit |
| user-name | ❌ No | Dash (-) not allowed |
| file.path | ❌ No | Dot (.) means “attribute,” not part of a name |
| my var | ❌ No | Spaces not allowed |
| return | ❌ No | return is a reserved Python keyword |
Test Variable Names
Experiment with variable names below. The current syntax will result in a SyntaxError. Try to fix it, or explore the errors generated by other non-valid names like my.var, return, or 2nd_var.
Functions
Functions create reusable code which can simplify tasks, allow iterative runs, and can make your code much more powerful. Python comes with some builtin functions which will help demonstrate. The previous section already introduced print and type. The table below outlines some more of the most commonly used options.
| Function | Example | Meaning | Result |
|---|---|---|---|
| help | help(len) | Displays documentation about an object or function | Shows usage info in console |
| len | len([1, 2, 3]) | Returns the number of items in an object | 3 |
| print(‘Hello’) | Outputs text or variables to the console | Hello | |
| type | type(3.14) | Returns the data type of an object | <class ‘float’> |
| min | min(4, 7, 2) | Returns the smallest of the given values | 2 |
| max | max(4, 7, 2) | Returns the largest of the given values | 7 |
| str | str(123) | Converts a value to a string | ‘123’ |
| int | int(3.9) | Converts a value to an integer (truncates decimals) | 3 |
| float | float(‘3.14’) | Converts a value to a floating-point number | 3.14 |
Function Exploration
In the first cell, a list is defined as my_list. After running it, use the second cell to explore more functions like: len, min, max, and type.