Python programs operate on objects with explicit input, ownership and failure contracts.
Learning roadmap
This section contains 40 written lessons or quiz banks. Programs are verified on CPython 3.14.6. Standard-library lessons target 3.11+ syntax; lessons using data, web, machine-learning or testing packages state their tested dependencies separately. Framework programs use local test clients, not a deployed service. Read the stated limits before adapting a fixture into an application.
Deferred calls and cleanup
Read the contract, run its program and inspect the failure case.
- Python generators: lazy iteration does not make retained output free
- Python decorators: preserve metadata and expose wrapper behavior
- Python closures: capture loop values at the intended time
- Python context managers: clean up on success and failure
- Python dataclasses: frozen fields require an immutable value model
Task and worker ownership
Read the contract, run its program and inspect the failure case.
- Python asyncio TaskGroup: cancel sibling work and retain failure evidence
- Python thread pools: collect results and observe worker failures
Object protocols and lookup
Read the contract, run its program and inspect the failure case.
- Python iterators: exhaustion and repeatable collection ownership
- Python descriptors: field validation and attribute precedence
- Python super and method resolution: cooperate across mixins
- Python Protocol: structural intent without runtime validation
Processes, locks and async budgets
Read the contract, run its program and inspect the failure case.
- Python process pools: importable workers and serialization costs
- Python subprocess: argument vectors, exit codes and bounded fixtures
- Python locks: protect the complete inventory transition
- Python asyncio.Queue: backpressure and completion accounting
- Python asyncio timeout: cancellation and cleanup ownership
Layout, lifetime and resource acquisition
Read the contract, run its program and inspect the failure case.
- Python slots: attribute layout without deep immutability
- Python weak references: a cache does not own its values
- Python ExitStack: unwind partially acquired resources
Class construction, grouped failures and execution context
Read the contract, run its program and inspect the failure case.
- Python metaclasses: validate a class before registering its wire format
- Python ABC: prevent construction of an incomplete implementation
- Python ExceptionGroup: handle selected failures and retain the rest
- Python ContextVar: task-local labels without sharing one global binding
- Python lru_cache: bound retention and include the revision in the key
Declaration hooks, producer lifetime and narrowing ownership
Read the contract, run its program and inspect the failure case.
- Python __init_subclass__: validate declarations without a custom metaclass
- Python async generators: close a suspended producer when leaving early
- Python TypeGuard: a static narrowing claim is not lasting ownership
Suspension, cancellation and shared predicates
Read the contract, run its program and inspect the failure case.
- Python generator send and close: suspension retains state until cleanup
- Python asyncio shield: caller cancellation does not transfer task ownership
- Python Condition: wait for protected state, not for a notification count
Transferred cleanup and type protocols
Read the contract, run its program and inspect the failure case.
- Python ExitStack pop_all: transfer cleanup without discarding it
- Python ExceptionGroup split: retain the nested failure structure
- Python singledispatch: dispatch follows the first argument’s type
- Python rich comparison: return NotImplemented for unsupported operands
Async workers and cached state
Read the contract, run its program and inspect the failure case.
- Python asyncio.to_thread: carry context into blocking work
- Python cached_property: delete the instance value when source state changes
- Python asyncio.gather: a sibling can continue after the first failure
Buffered readers and deadlines
Read the contract, run its program and inspect the failure case.
- Python itertools.tee: a lagging reader retains buffered values
- Python asyncio.timeout: catch the deadline outside the context
Copying records without copying ownership
Read the contract, run its program and inspect the failure case.
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