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Learn fundamentals

Short quizzes that build the mental models behind the language. No hand-holding - answer, see why, move on.

Python

Variables, functions, classes, decorators, regex, type hints, and more — the mechanics that trip people up when it matters.

16 topics192+ questions

SQL

SELECT, filtering, joins, aggregation, window functions, and the NULL edge cases that catch everyone off guard.

17 topics170+ questions

Recommended order

Each topic builds on the one before. Start at step 1 and work down.

Python

Foundation
1
Variables & Types

where everything starts

2
Control Flow

if / for / while

3
Lists
4
Dictionaries
5
Functions
6
Strings
Intermediate
7
Comprehensions

Python's superpower

8
Error Handling
9
Iterators & Generators

lazy evaluation, memory efficiency

Advanced
10
Classes
11
Functional Tools

map, filter, lambda, partial

12
Decorators

wrapping functions, @wraps, factories

13
Modules & Packages
14
File I/O

pathlib, csv, json

15
Regular Expressions
16
Type Hints

Optional, TypedDict, Protocol

SQL

Foundation
1
SELECT Basics

where everything starts

2
Filtering

WHERE clause

3
Sorting
4
Aggregation

COUNT, SUM, AVG

5
Grouping

GROUP BY

6
Filtering Groups

HAVING

Core
7
Joins

most tested concept

8
Self Joins
9
Subqueries
10
CTEs

cleaner than nested subqueries

11
CASE Expressions
12
Set Operations

UNION, INTERSECT, EXCEPT

Advanced
13
Window Functions

hardest topic, do last

14
Date Filtering
15
Date Functions
16
String Functions
17
Distinct

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