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Courses / Programming

Python

Plain Python for analysts, practiced in a real notebook.

Start lesson 1Practice interviewTake the assessmentPractice the first unit of every course. No account needed.
72lessons
432checked exercises
13projects, cases and exams
Prepares you for Coding interviews

Projects, case studies and mock exams

Project · IntermediateExpense report from a messy CSV

Turn a hand-edited expense export into a clean March summary by team: duplicates, blank and formatted amounts, two date formats, and a CSV deliverable.

8 steps · 45 minCase study · IntermediateWhich support channel is fastest

Answer a support lead's question with ticket data: hours to resolve per channel, mean against median, and a recommendation backed by the numbers.

6 steps · 35 minProject · AdvancedWeb log parser

Turn a raw web access log into error rates per endpoint and per hour: regex parsing, malformed lines, normalized paths and a small report.

8 steps · 50 minProject · AdvancedBudget tracker

Track a team's spend against its budget with exact money: load JSON and CSV, model transactions as dataclasses, find overspends and print a monthly report.

8 steps · 50 minCase study · AdvancedLate deliveries from an orders API

Pull every page of an orders API, keep the delivered orders, measure lateness per carrier and say which carrier is late most often.

6 steps · 40 minMock exam · ExpertEntry-level certification style

Twelve timed questions in the style of entry-level Python certifications: predict the output, then write small functions.

12 questions · 30 minProject · ExpertText-analysis tool

Turn free-text survey comments into themes: clean and tokenize, remove stop words, count words and word pairs, tag themes with regular expressions, and pull quotes.

7 steps · 50 minCase study · ExpertThe March sales drop

Investigate a fall in March revenue: net revenue by month, return rates, prices and missing data, then name the explanation the numbers support.

6 steps · 40 minProject · ExpertFrom raw exports to a monthly report

Combine two raw exports in different formats into one tested monthly report: encodings, European number formats, date formats, currency conversion, duplicates and a CSV deliverable.

6 steps · 60 minMock exam · ExpertAnalyst Python screen

Ten timed tasks in the style of a data analyst's live Python screen: cleaning values, grouping, ranking, joining, dates and outliers.

10 questions · 45 min

Practice the Python that analysts use at work, from your first variable to interview-ready algorithms: cleaning text, adding up and grouping records, reading CSV and JSON files, dates, regular expressions, classes, tests and small functions you can rely on. Every exercise runs real Python in a Jupyter-style notebook in your browser, so the output, errors and tracebacks match what you'll see at work.

Lessons teach one skill with a short example, then give you exercises that start guided and end with a workplace task. Practice lessons mix skills on fresh data, and projects take a messy request from raw input to a finished report. Your code runs on the data you see and on a hidden copy with different values, and a wrong answer gets a specific hint.

The course ends with interview sets and timed mock exams. pandas has its own course.

Interview practice

Explain what you've learned in a full-screen interview. Speak or type, then review your answers against the rubric for your level.

Interview loops by job

Beginner

FreeNo account or card needed. Every lesson in this unit is yours to practice.

Basics

Variables, types, text and numbers: the values every script works with.

5 lessons
1Variables and data typesStore values in variables, check their type, and turn text into numbers before you do math with it.4 exercises · 10 minFree
2Strings and f-stringsClean up text with string methods, slice out the parts you need, and build report lines with f-strings and number formats.5 exercises · 15 minFree
3Numbers and arithmeticDivide, round and find remainders the way Python does, and get percent change and order of operations right.4 exercises · 12 minFree
4True, False and NoneCount with booleans, know which values count as false, test for a missing value with None, and compare floats safely.5 exercises · 15 minFree
Practice setBasics practiceMixed practice on variables, text, numbers and booleans, using a shift-scheduling export.Free

Collections

Lists, dictionaries, sets and tuples, and the nested data you get from files and APIs.

6 lessons
6Lists: index, slice, sort and addPick items by position, slice out runs of them, sort without losing your list, and add items one at a time or in bulk.4 exercises · 15 minWith a plan
7Dictionaries: look up, update and addLook values up by key, update counts, handle missing keys with get(), and build a dictionary from two lists.5 exercises · 15 minWith a plan
8Sets and tuplesRemove duplicates and compare groups with sets, and unpack fixed records with tuples.4 exercises · 12 minWith a plan
9Nested data: lists of dictionariesWork with rows of records: total a field, build a lookup by id, handle missing fields and group values into lists.5 exercises · 20 minWith a plan
10Copies and referencesSee why a list changes "by itself", copy lists and dictionaries properly, and avoid the shared inner list.5 exercises · 20 minWith a plan
Practice setCollections practiceMixed practice on lists, dictionaries, sets, tuples, nested data and copies, using a gym membership list.With a plan

Control flow

Decisions, loops and comprehensions, with the patterns analysts write every day.

5 lessons
12Decisions with if, elif and elseRun code only when a condition holds, choose between several bands in the right order, and combine conditions with and and or.5 exercises · 15 minWith a plan
13for and while loopsRepeat work for every item with for, keep a running total, number lines with enumerate, walk lists together with zip, and repeat until a condition changes with while.5 exercises · 20 minWith a plan
14Loop patterns: totals, best so far, flags and breakWrite the loops analysts use every day: running balances, the best item so far, a flag with break, loop else, and the longest streak.5 exercises · 20 minWith a plan
15List and dictionary comprehensionsTransform and filter a list in one line, build or invert a dictionary, and flatten nested lists.5 exercises · 15 minWith a plan
Practice setControl flow practiceMixed practice on if, loops, loop patterns and comprehensions, using a gym class timetable.With a plan

Functions

Write functions that return values, take options and handle bad input.

4 lessons
17Write functions that return valuesPackage a calculation as a function, return its result instead of printing it, and put the return in the right place.5 exercises · 20 minWith a plan
18Arguments, defaults and returning several valuesGive arguments default values, call functions with named arguments, return several values at once, and avoid the shared default list.4 exercises · 20 minWith a plan
19Handle errors with try and exceptCatch the error you expect, skip bad values without stopping, and raise your own error when input makes no sense.5 exercises · 20 minWith a plan
Practice setFunctions practiceTen small utility functions of the kind analysts keep in a helpers file, each checked on hidden edge cases.With a plan

Intermediate

Working with data

CSV and JSON files, dates, sorting, counting and grouping, and files in other encodings.

7 lessons
21Read and write CSV filesRead a CSV file into dictionaries, convert its text values, filter and total the rows, and write a summary file.5 exercises · 20 minWith a plan
22Working with JSON dataParse JSON from an API or a file, reach into nested data, handle missing fields, and write JSON back out.5 exercises · 20 minWith a plan
23Dates and times with datetimeTurn text into dates, add days, measure the time between two moments in hours, find weekends, and format dates back into text.5 exercises · 20 minWith a plan
24Sort with key and lambdaSort text without caring about capitals, sort records by a field, rank a dictionary by its values, and sort by two things at once.5 exercises · 20 minWith a plan
25Count and group with Counter and defaultdictCount things and find the most common with Counter, group records with defaultdict(list), and total them with defaultdict(float).5 exercises · 20 minWith a plan
26Files, folders and encodingsRead and write text files with pathlib, find files by pattern, append to a log, and open exports saved in other encodings.5 exercises · 20 minWith a plan
Practice setWorking with data practiceMixed practice on CSV, JSON, dates, sorting, counting and files, using a small hotel's booking export.With a plan

Text and regular expressions

Clean messy text, then find, extract and validate patterns with regular expressions.

4 lessons
28Cleaning textNormalize spaces and capitals, compare text without caring about case or accents, strip punctuation and pad codes.5 exercises · 20 minWith a plan
29Regular expressions: search and findallFind order numbers, amounts and references in free text with re.findall and re.search, and avoid the classic traps.5 exercises · 25 minWith a plan
30Regex groups, sub and validationCapture parts of a match with groups and named groups, replace text with re.sub, and validate whole values with fullmatch.5 exercises · 25 minWith a plan
Practice setText practiceMixed practice on cleaning text and regular expressions, using a support inbox export.With a plan

Standard library

Modules you already have: imports, itertools, functools, statistics and Decimal for money.

6 lessons
32Modules, imports and randomImport modules three ways, use math and random, make random results repeatable, and avoid hiding a module behind a variable.5 exercises · 20 minWith a plan
33itertools for analystsRunning totals with accumulate, groups with groupby, pairs with combinations, every option with product, and flattening with chain.5 exercises · 20 minWith a plan
34lambda, map, filter and functoolsWrite small functions inline with lambda, transform and filter with map and filter, combine with reduce, and preset arguments with partial.5 exercises · 20 minWith a plan
35statistics: mean, median and quantilesDescribe data with mean, median, mode, standard deviation and quartiles, and handle ties, outliers and empty data.5 exercises · 20 minWith a plan
36Decimal for moneyAdd up money exactly with Decimal, build it from text, round half up to the cent, and split a bill so the shares add up.5 exercises · 20 minWith a plan
Practice setStandard library practiceMixed practice on math, random, itertools, functools, statistics and Decimal, using a coffee chain's weekly numbers.With a plan

Intermediate projects

Real requests, start to finish: a messy expense export and a support-channel question.

2 lessons
ProjectExpense report from a messy CSVTurn a hand-edited expense export into a clean March summary by team: duplicates, blank and formatted amounts, two date formats, and a CSV deliverable.With a plan
Case studyWhich support channel is fastestAnswer a support lead's question with ticket data: hours to resolve per channel, mean against median, and a recommendation backed by the numbers.With a plan

Advanced

Functions in depth

Scope, closures, generators, decorators and recursion.

5 lessons
40Scope and closuresUnderstand local and global names, fix UnboundLocalError, build functions that remember values, and avoid late binding in loops.5 exercises · 25 minWith a plan
41Generators and iteratorsProduce values lazily with yield, take the first match with next and a default, avoid exhausted iterators, and work with endless sequences.5 exercises · 25 minWith a plan
42DecoratorsWrap functions to add logging, checks and retries without changing them, keep their return values and names, and write decorators that take options.5 exercises · 30 minWith a plan
43RecursionWalk nested folders, lists, org charts and JSON with functions that call themselves, and always give them a way to stop.5 exercises · 25 minWith a plan
Practice setFunctions in depth practiceMixed practice on closures, generators, decorators and recursion, built around a small reporting toolkit.With a plan

Classes

Model records and behavior with classes, dataclasses and inheritance.

4 lessons
45Classes and objectsBundle data and behavior in a class: __init__ and self, methods, instance versus class attributes, a readable __repr__, and computed properties.5 exercises · 30 minWith a plan
46DataclassesDefine record types in a few lines with @dataclass: defaults, list fields, sorting, immutable records, validation and conversion to dictionaries.5 exercises · 30 minWith a plan
47Inheritance and polymorphismBuild on a class with a subclass, call the parent with super(), override methods so different objects answer the same call, and define your own exceptions.5 exercises · 30 minWith a plan
Practice setClasses practiceMixed practice on classes, dataclasses and inheritance, modeling a small warehouse: items, shelves, stock moves and alerts.With a plan

Reliable code

Read tracebacks, log what happens, test your functions and add type hints.

4 lessons
49Debugging, tracebacks and loggingRead a traceback from the bottom up, log what a script does at the right level, and record errors with enough context to fix them.5 exercises · 25 minWith a plan
50Testing with assert and unittestWrite tests that pass on correct code and fail on buggy code: assert, edge cases, float comparisons and unittest with assertRaises.5 exercises · 30 minWith a plan
51Type hintsAnnotate arguments and results, describe lists, dictionaries and optional values, and remember that hints document types without converting them.5 exercises · 25 minWith a plan
Practice setReliable code practiceMixed practice on logging, tests, assertions and type hints for a small payroll import.With a plan

APIs and projects

Data from APIs, a log parser, a budget tracker and an orders case study.

4 lessons
53Working with APIsCall a JSON API the way analysts do: check the status code, page through results, handle errors and rate limits, and flatten nested records.5 exercises · 30 minWith a plan
ProjectWeb log parserTurn a raw web access log into error rates per endpoint and per hour: regex parsing, malformed lines, normalized paths and a small report.With a plan
ProjectBudget trackerTrack a team's spend against its budget with exact money: load JSON and CSV, model transactions as dataclasses, find overspends and print a monthly report.With a plan
Case studyLate deliveries from an orders APIPull every page of an orders API, keep the delivered orders, measure lateness per carrier and say which carrier is late most often.With a plan

Expert

Algorithms

Complexity and the patterns coding interviews test: binary search, two pointers, hashing, windows and intervals.

7 lessons
57Complexity and Big OEstimate how work grows with input size, spot the hidden loop in `x in list`, and replace quadratic code with lookups and running totals.5 exercises · 30 minWith a plan
58Binary search and bisectFind items in sorted data by halving the search range, use bisect for brackets and ranges, and avoid the off-by-one that loops forever.5 exercises · 30 minWith a plan
59Two pointersWalk two positions through sorted data or from both ends: palindromes, merging sorted lists, pairs with a target sum and closest matches.5 exercises · 30 minWith a plan
60Hashing patternsUse dictionaries and sets for the classic O(n) answers: first repeat, two values that add up, anagram groups, first unique item and the longest run.5 exercises · 30 minWith a plan
61Sliding windowAnswer questions about runs of consecutive items in one pass: fixed windows with a running sum, and growing and shrinking windows for the longest or shortest run.5 exercises · 30 minWith a plan
62Intervals: merge and overlapWork with (start, end) ranges like bookings and shifts: merge overlaps, total covered time, find gaps, count rooms needed and intersect two schedules.5 exercises · 30 minWith a plan
Practice setAlgorithms practiceTen mixed problems from the algorithms unit on analyst data: lookups, binary search, two pointers, windows and intervals, with large hidden inputs.With a plan

Interview practice

Interview questions by difficulty and timed mock exams.

5 lessons
64Python interview questions for data analystsFive classic plain-Python interview tasks, set in analyst work: word counts, second highest value, missing IDs, two payments that match a total, and a moving average.5 exercises · 40 minWith a plan
Interview setEasySix warm-up interview questions on strings, lists and dictionaries, each checked on hidden edge cases.With a plan
Interview setMediumSix medium interview questions: best time to buy and sell, top k words, balanced brackets, run-length encoding, grouping and percent change.With a plan
Interview setHardSix harder interview questions: common prefixes, an LRU cache, top spender per month, parsing durations, task ordering with cycles, and sessionizing events.With a plan
Mock examEntry-level certification styleTwelve timed questions in the style of entry-level Python certifications: predict the output, then write small functions.With a plan

Capstone projects

End-to-end analyst work: a text-analysis tool, a sales investigation and a reporting pipeline.

4 lessons
ProjectText-analysis toolTurn free-text survey comments into themes: clean and tokenize, remove stop words, count words and word pairs, tag themes with regular expressions, and pull quotes.With a plan
Case studyThe March sales dropInvestigate a fall in March revenue: net revenue by month, return rates, prices and missing data, then name the explanation the numbers support.With a plan
ProjectFrom raw exports to a monthly reportCombine two raw exports in different formats into one tested monthly report: encodings, European number formats, date formats, currency conversion, duplicates and a CSV deliverable.With a plan
Mock examAnalyst Python screenTen timed tasks in the style of a data analyst's live Python screen: cleaning values, grouping, ranking, joining, dates and outliers.With a plan

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