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Courses / Programming

Python for software engineers

Build, test and debug Python programs in a code editor with real execution and hidden tests.

Start lesson 1Practice interviewTake the assessmentPractice the first unit of every course. No account needed.
67lessons
350checked exercises
16projects, cases and exams
Prepares you for Python software engineering and coding interviews

Projects, case studies and mock exams

Project · BeginnerRelease-list CLI project

Harbor Media keeps release artifacts in a text file assembled by several teams.

6 stepsCase study · BeginnerScheduling incident-log case

Larch Scheduling is preparing a release of its appointment-routing service.

5 stepsProject · IntermediateLibrary lending project

Build a library loan service with ownership and reservations.

6 stepsProject · IntermediateIncident log parser project

Build a checked incident summary from imperfect service logs.

6 stepsProject · IntermediateMocked REST client project

Build a deterministic client for a supplied mock API.

6 stepsProject · IntermediateLegacy settlement refactor

Refactor a settlement calculation with executable protection first.

6 stepsProject · AdvancedMedia metadata cache

Cedar Media repeatedly loads metadata for recently viewed clips.

6 steps · 40 minProject · AdvancedLogistics event service

Fern Logistics receives a mixture of parcel jobs, control events and retried deliveries.

6 steps · 40 minProject · AdvancedLegacy checkout refactor

Juniper Retail has a checkout calculation that grew by adding conditions to one loop.

6 steps · 40 minProject · ExpertTravel request limiter

Harbor Travel needs a limiter that explains every admission decision.

6 steps · 40 minCase study · ExpertMedia delivery incident

Cedar Media's support team sees failed delivery rows and wants to isolate a noisy tenant.

5 steps · 20 minMock exam · ExpertService implementation job test

This original job-test simulation gives you a service team's small implementation queue.

8 questions · 55 minMock exam · ExpertDesign and internals job test

This second original job-test simulation shifts the emphasis to language behavior and small domain designs.

8 questions · 60 min

Write Python for application development and technical interviews. Start with values, references and function calls, then build classes, typed interfaces and standard-library programs. Each lesson gives you a worked example and a sequence of coding tasks with boundary checks.

Projects build CLI tools, a mocked REST client, log parsers, caches, rate limiters and asynchronous services. Your code carries from one project step to the next. Practice sets, design interviews and timed job tests use fresh fictional data.

Python runs in your browser. File exercises use a virtual filesystem, external APIs use local fixtures, and concurrency lessons state where host threads and processes differ. Type annotations are taught alongside runtime contracts; this workspace does not run a static type checker.

Beginner

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

Values and references

Write predictable functions over values, collections, and independent copies.

5 lessons
1Python values and boundariesA release tool takes text and numbers from files, calculates a result, and returns it to another program.4 exercisesFree
2Truth, equality, and identityA configuration value can be present even when it's zero or empty.4 exercisesFree
3Mutation and independent copiesA copied configuration can still share its nested lists with the original.4 exercisesFree
4Collections and lookup rulesLists keep order and allow repeated values.4 exercisesFree
Practice setValues and references practiceA maintenance team at Cedar Transit needs several small data helpers before its next release.Free

Functions and iteration

Build reusable functions, closures, wrappers, and lazy iteration pipelines.

7 lessons
6Function arguments and defaultsA function contract says which values callers provide and which choices the function owns.4 exercisesWith a plan
7Closures and captured stateAn inner function can use names from its enclosing function.4 exercisesWith a plan
8Comprehensions and transformationsA comprehension builds a collection from an iterable.4 exercisesWith a plan
9Iterators and generatorsAn iterable can supply an iterator.4 exercisesWith a plan
10Decorators and transparent wrappersA decorator takes a function and returns a callable, often a wrapper that adds behavior around the original call.4 exercisesWith a plan
ProjectRelease-list CLI projectHarbor Media keeps release artifacts in a text file assembled by several teams.With a plan
Practice setFunctions and iteration practiceYou are preparing reusable helpers for a fictional delivery platform.With a plan

Resources and libraries

Handle failures, close resources, and use standard-library data formats and modules.

6 lessons
13Exceptions and domain boundariesAn exception interrupts normal control flow and carries information about a failure.4 exercisesWith a plan
14Context managers and resource lifetimesA context manager defines what happens when a with block starts and when it ends.4 exercisesWith a plan
15Standard-library data boundariesThe standard library handles common formats without a dependency install.4 exercisesWith a plan
16Modules and packaging conceptsA module is a Python file with its own namespace.4 exercisesWith a plan
Case studyScheduling incident-log caseLarch Scheduling is preparing a release of its appointment-routing service.With a plan
Practice setResources and libraries practiceA fictional engineering team is preparing a handoff for its next maintainer.With a plan

Intermediate

Domain models

Model Python values, invariants, inheritance, and loan ownership.

6 lessons
19Object protocolsGive domain objects familiar Python behavior.4 exercisesWith a plan
20Properties and instance stateProtect object invariants and keep mutable state separate.4 exercisesWith a plan
21Inheritance and compositionChoose explicit inheritance or a composed dependency.4 exercisesWith a plan
22Dataclasses and enumsRepresent small values and validate external states.4 exercisesWith a plan
ProjectLibrary lending projectBuild a library loan service with ownership and reservations.With a plan
Practice setDomain model practiceApply value identity, validation, ownership, and state transitions.With a plan

Standard library tools

Transform application data with collections, iterators, heaps, parsers, and virtual files.

6 lessons
25Purpose-built collectionsChoose containers for counting, grouping, queues, and precedence.4 exercisesWith a plan
26Iterators and reusable functionsCompose standard iterators and inspect cached work.4 exercisesWith a plan
27Heaps and sorted boundariesSelect priorities and locate exact ranges in sorted values.4 exercisesWith a plan
28Text, time, JSON, and filesHandle application boundaries with explicit formats and cleanup.4 exercisesWith a plan
ProjectIncident log parser projectBuild a checked incident summary from imperfect service logs.With a plan
Practice setStandard library practiceChoose standard-library tools on fresh application data.With a plan

Reliable service boundaries

Protect service code with tests, typed contracts, logging, and bounded mock clients.

7 lessons
31A small test runnerWrite executable checks that keep running after failures.4 exercisesWith a plan
32Fixtures and mock dependenciesIsolate cases and replace external work with controlled dependencies.4 exercisesWith a plan
33Typed interfaces and runtime contractsDocument reusable interfaces and validate external data explicitly.4 exercisesWith a plan
34Application loggingCapture useful records without global logging side effects.4 exercisesWith a plan
ProjectMocked REST client projectBuild a deterministic client for a supplied mock API.With a plan
ProjectLegacy settlement refactorRefactor a settlement calculation with executable protection first.With a plan
Practice setService boundary practiceCheck fresh service contracts and explicit recovery decisions.With a plan

Advanced

Performance and caches

Count work, profile calls and build a cache with explicit invalidation and eviction.

5 lessons
38Built-in operation costsA list search compares values until it finds a match.4 exercises · 20 minWith a plan
39Deterministic profilingA profiler can show that a normalizer ran thousands of times even when each call looked harmless in isolation.4 exercises · 20 minWith a plan
40Memoization contractsA cached quote is useful only while its key identifies the same calculation.4 exercises · 20 minWith a plan
ProjectMedia metadata cacheCedar Media repeatedly loads metadata for recently viewed clips.With a plan
Practice setPerformance practiceThe operations team has sent a new mixture of traces, quote requests and cache commands.With a plan

Concurrency and event services

Separate thread and process models from executable coroutine and queue work.

5 lessons
43Threads and the GILTwo workers can each read the same counter and then overwrite one another's increment.4 exercises · 20 minWith a plan
44Process boundariesA process pool works best when a job has a clear input and a clear result.4 exercises · 20 minWith a plan
45Running coroutinesCalling an async function creates a coroutine object.4 exercises · 20 minWith a plan
ProjectLogistics event serviceFern Logistics receives a mixture of parcel jobs, control events and retried deliveries.With a plan
Practice setConcurrency practiceA release review mixes workload choices, worker payloads and coroutine results.With a plan

Maintainable services

Refactor policy boundaries and preserve structured operational evidence.

5 lessons
48Pure refactoring boundariesA checkout function becomes difficult to change when validation, price lookup, normalization and formatting all update the same variables.4 exercises · 20 minWith a plan
50Structured service loggingA useful incident log lets you follow one request without exposing its credentials.4 exercises · 20 minWith a plan
ProjectLegacy checkout refactorJuniper Retail has a checkout calculation that grew by adding conditions to one loop.With a plan
Interview setPython internals: easyA short Python interview question often tests whether you can explain a surprising result and then repair the contract.With a plan
Practice setMaintainability practiceA different service team has sent code contracts for review.With a plan

Expert

Traffic and failure control

Control quotas, cancellation and bounded delivery with recoverable outcomes.

5 lessons
54Cooperative cancellationCanceling a task requests that it stop at a cooperative boundary.4 exercises · 20 minWith a plan
55Bounded flow controlA fast producer can fill memory while a slower consumer works correctly on every individual item.4 exercises · 20 minWith a plan
ProjectTravel request limiterHarbor Travel needs a limiter that explains every admission decision.With a plan
Case studyMedia delivery incidentCedar Media's support team sees failed delivery rows and wants to isolate a noisy tenant.With a plan
Practice setTraffic-control practiceA new service has the same familiar failure modes with different request patterns.With a plan

Domain modeling

Implement ownership, allocation and guarded transitions in bounded designs.

5 lessons
58Library circulation designA library copy can have one active borrower, while a title can have several people waiting.4 exercises · 20 minWith a plan
59Parking allocation designA parking allocator needs more than a free-space count.4 exercises · 20 minWith a plan
60Elevator dispatch designAn elevator controller combines dispatch decisions with safety constraints.4 exercises · 20 minWith a plan
Interview setPython design: mediumA design interview becomes concrete when the interviewer asks what happens on the second request, the wrong owner or a circular dependency.With a plan
Practice setDomain-model practiceA product team has changed the records but kept the domain policies.With a plan

Interview and job-test readiness

Defend language and service invariants on fresh timed and untimed work.

5 lessons
63Adversarial service contractsA function can pass its happy example and still break when two windows touch, a dependency repeats or a retried event carries a zero effect.4 exercises · 20 minWith a plan
Interview setPython engineering: hardA harder engineering round asks you to defend several invariants at once.With a plan
Mock examService implementation job testThis original job-test simulation gives you a service team's small implementation queue.With a plan
Mock examDesign and internals job testThis second original job-test simulation shifts the emphasis to language behavior and small domain designs.With a plan
Practice setEngineering transfer practiceYour final practice queue crosses language internals, service operations and domain design.With a plan

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