Python Software Engineering Examples

A practical collection of small Python examples for learning software engineering concepts step by step — from zero to advanced.

The repository follows a learning path: Python fundamentals, functions, classes, data structures, OOP, SOLID, design patterns, system design, concurrency, and advanced topics.

Each example is intentionally small and self-contained so it can be read, run, and modified without needing a full application setup.

Repository Structure

PSE_000_Python_Basics/         Variables, types, loops, strings, lists, dicts, tuples, sets
PSE_010_Functions/             Basics, parameters, args/kwargs, lambda, closures, decorators
PSE_020_Builtins/              range, enumerate, zip, map, filter, sorted, any/all
PSE_030_Iterators_Generators/  Iterable, iterator, generator, yield
PSE_040_Input_Output/          stdin, print, file I/O, pathlib, serialization
PSE_050_Modules/               Imports, packages, venv, dependency management
PSE_060_Error_Handling/        Exceptions, custom exceptions, context managers
PSE_070_Classes/               Attributes, methods, properties, dataclasses
PSE_080_OOP/                   12 core OOP concepts
PSE_090_Data_Structures/       Stack, queue, linked list, heap, tree, graph
PSE_100_Type_Hints/            Basic typing, generics, protocols, type aliases
PSE_110_Concurrency/           CPU vs IO bound, threads, multiprocessing, asyncio
PSE_120_SOLID/                 5 SOLID principles with examples
PSE_130_Design_Patterns/       23 GoF + 1 behavioral patterns
PSE_135_Architectural_Patterns/ 5 enterprise architectural patterns
PSE_140_Testing/               unittest, pytest, mocking, fixtures
PSE_150_Standard_Library/      collections, itertools, functools, datetime, json, logging
PSE_160_System_Design/         17 distributed systems topics
PSE_170_Algorithms/            Big-O complexity, algorithm analysis
PSE_180_CLI_Frameworks/        argparse, click, typer
PSE_190_Serialization/         pydantic, orjson, yaml, toml, msgpack
PSE_200_Logging_Advanced/      structlog, loguru
PSE_210_HTTP_Client/           httpx, requests
PSE_220_Database/              SQLAlchemy ORM, sqlite3
PSE_230_Web_Frameworks/        FastAPI, Flask
PSE_240_Terminal_UI/           rich, textual
PSE_250_GUI/                   tkinter (standard library)
PSE_260_Packaging/             pyproject.toml, uv package manager
PSE_270_Capstone/              Full API server project

Folder names use this convention:

PSE_<NUMBER>_<TOPIC_NAME>

PSE means Python Software Engineering. Numbers follow a learning path from 000 (beginner) to 270 (advanced).

Learning Path (000 → 270)

Level	Folder	Topic	What You Learn
000	PSE_000	Python Basics	Variables, types, control flow, collections
010	PSE_010	Functions	Parameters, return values, scope, closures, decorators
020	PSE_020	Builtins	range, enumerate, zip, map, filter, sorted
030	PSE_030	Iterators / Generators	Iterable protocol, generator functions, yield
040	PSE_040	Input / Output	print, input, file I/O, pathlib, serialization
050	PSE_050	Modules	Imports, packages, virtual environments, pip
060	PSE_060	Error Handling	try/except, custom exceptions, context managers
070	PSE_070	Classes	Attributes, methods, properties, dataclasses
080	PSE_080	OOP	12 core OOP concepts
090	PSE_090	Data Structures	Stack, queue, linked list, heap, tree, graph
100	PSE_100	Type Hints	Basic typing, generics, protocols
110	PSE_110	Concurrency	Threads, multiprocessing, async/await
120	PSE_120	SOLID	5 SOLID principles with examples
130	PSE_130	Design Patterns	23 GoF + 1 behavioral patterns
135	PSE_135	Architectural Patterns	5 enterprise architectural patterns
140	PSE_140	Testing	unittest, pytest, mocking, fixtures
150	PSE_150	Standard Library	collections, itertools, functools, datetime, json
160	PSE_160	System Design	17 distributed systems topics
170	PSE_170	Algorithms	Big-O complexity, algorithm analysis
180	PSE_180	CLI Frameworks	argparse, click, typer
190	PSE_190	Serialization	pydantic, orjson, yaml, toml, msgpack
200	PSE_200	Logging Advanced	structlog, loguru
210	PSE_210	HTTP Client	httpx, requests
220	PSE_220	Database	SQLAlchemy ORM, sqlite3
230	PSE_230	Web Frameworks	FastAPI, Flask
240	PSE_240	Terminal UI	rich, textual
250	PSE_250	GUI	tkinter (standard library)
260	PSE_260	Packaging	pyproject.toml, uv
270	PSE_270	Capstone	Full API server project

Topics Covered

PSE_000 — Python Basics (9 files)

#	File	Topics
01	PB_01_variables.py	Variables, dynamic typing, unpacking
02	PB_02_data_types.py	int, float, str, bool, None
03	PB_06_strings.py	String operations, formatting
04	PB_07_conditionals.py	if / elif / else, ternary
05	PB_08_loops.py	for, while, enumerate, zip
06	PB_09_lists.py	Lists, slicing, comprehensions
07	PB_10_tuples.py	Tuples, named tuples
08	PB_11_dictionaries.py	Dicts, comprehensions
09	PB_12_sets.py	Sets, frozenset, set operations

PSE_010 — Functions (9 files)

#	File	Topic
01	FN_01_basic_functions.py	def, params, return, docstrings
02	FN_02_parameters.py	Positional, keyword, default, *args, **kwargs
03	FN_03_return_values.py	Return types, multiple returns, tuples
04	FN_04_scope.py	LEGB rule, global, nonlocal
05	FN_05_args_kwargs.py	*args, **kwargs, combined signatures
06	FN_06_lambda.py	Lambdas, map, filter, sorted
07	FN_07_first_class_functions.py	Passing and returning functions
08	FN_08_closures.py	nonlocal, factory functions
09	FN_09_decorators.py	@syntax, stacking, practical examples

PSE_020 — Builtins (10 files)

#	File	Topic
01	BI_01_range.py	range, sequences, loops
02	BI_02_enumerate.py	Index + value iteration
03	BI_03_zip.py	Combining iterables
04	BI_04_map.py	Applying functions to iterables
05	BI_05_filter.py	Filtering elements
06	BI_06_sorted.py	Sorting with key functions
07	BI_07_reversed.py	Reversing sequences
08	BI_08_any_all.py	Boolean aggregation
09	BI_09_sum_min_max.py	Numeric builtins
10	BI_10_iter_next.py	Iterator protocol

PSE_030 — Iterators / Generators (5 files)

#	File	Topic
01	IT_01_iterable.py	__iter__, __next__, for loop protocol
02	IT_02_iterator.py	Iterator protocol, custom iterators
03	IT_03_generator.py	Generator functions, lazy evaluation
04	IT_04_yield.py	yield, yield from, send()
05	IT_05_generator_expression.py	(expr for x in ...) syntax

PSE_040 — Input / Output (4 files)

#	File	Topic
01	IO_01_print_input.py	print(), input(), formatting
02	IO_02_file_io.py	open(), read/write, context managers
03	IO_03_pathlib.py	Path objects, glob, file operations
04	IO_04_serialization.py	json, pickle, csv

PSE_050 — Modules (4 files)

#	File	Topic
01	MD_01_import.py	import, from, as, __name__
02	MD_02_packages.py	__init__, subpackages, relative imports
03	MD_03_virtual_environment.py	venv, pip, pyproject.toml
04	MD_04_dependency_management.py	Requirements files, lock files

PSE_060 — Error Handling (3 files)

#	File	Topic
01	EH_01_exceptions.py	try/except/finally, exception hierarchy
02	EH_02_custom_exceptions.py	Raising, custom error classes
03	EH_03_context_managers.py	with statement, __enter__/__exit__

PSE_070 — Classes (10 files)

#	File	Topic
01	CL_01_class_basics.py	class, __init__, self
02	CL_02_instance_attributes.py	Instance variables, initialization
03	CL_03_class_attributes.py	Class-level state, shared data
04	CL_04_instance_methods.py	def methods, self parameter
05	CL_05_class_methods.py	@classmethod, factory methods
06	CL_06_static_methods.py	@staticmethod, utility functions
07	CL_07_properties.py	@property, getters, setters
08	CL_08_private_attributes.py	Name mangling, double underscore
09	CL_09_magic_methods.py	__str__, __repr__, __len__, operators
10	CL_10_dataclasses.py	@dataclass, field, frozen

PSE_080 — OOP (12 files)

#	Concept	File
01	Encapsulation	OOP_01_encapsulation.py
02	Inheritance	OOP_02_inheritance.py
03	Polymorphism	OOP_03_polymorphism.py
04	Abstraction	OOP_04_abstraction.py
05	Composition	OOP_05_composition.py
06	Aggregation	OOP_06_aggregation.py
07	Association	OOP_07_association.py
08	Delegation	OOP_08_delegation.py
09	Abstract Classes	OOP_09_abstract_classes.py
10	Duck Typing	OOP_10_duck_typing.py
11	Protocols	OOP_11_protocols.py
12	Mixins	OOP_12_mixins.py

PSE_090 — Data Structures (6 files)

#	File	Topic
01	DS_01_stack.py	LIFO, push/pop, balanced parentheses
02	DS_02_queue.py	FIFO, deque, BFS
03	DS_03_linked_list.py	Singly/doubly linked nodes
04	DS_04_heap.py	Min/max heap, heapq
05	DS_05_tree.py	TreeNode, BST, traversal
06	DS_06_graph.py	Adjacency list, BFS, DFS

PSE_100 — Type Hints (4 files)

#	File	Topic
01	TH_01_basic_typing.py	int, str, List, Dict, Optional
02	TH_02_generics.py	TypeVar, Generic, Callable
03	TH_03_protocols.py	Structural subtyping
04	TH_04_type_alias.py	Type aliases, NewType

PSE_110 — Concurrency (5 files)

#	File	Topic
01	CC_01_cpu_vs_io_bound.py	When to use threads vs processes
02	CC_02_threads.py	threading, Lock, GIL, thread safety
03	CC_03_multiprocessing.py	Process Pool, parallel CPU work
04	CC_04_asyncio.py	Event loop, coroutines, gather
05	CC_05_async_await.py	async def, await, async queues

PSE_120 — SOLID Principles (5 files)

#	Principle	File
01	Single Responsibility	SOLID_01_single_responsibility.py
02	Open/Closed	SOLID_02_open_closed.py
03	Liskov Substitution	SOLID_03_liskov_substitution.py
04	Interface Segregation	SOLID_04_interface_segregation.py
05	Dependency Inversion	SOLID_05_dependency_inversion.py

PSE_130 — Design Patterns (24 files)

Category	#	Pattern	File
Creational	1	Singleton	Creational/DP_C_01_singleton_pattern.py
	2	Factory Method	Creational/DP_C_02_factory_method_pattern.py
	3	Abstract Factory	Creational/DP_C_03_abstract_factory_pattern.py
	4	Builder	Creational/DP_C_04_builder_pattern.py
	5	Prototype	Creational/DP_C_05_prototype_pattern.py
Structural	1	Facade	Structural/DP_S_01_facade_pattern.py
	2	Adapter	Structural/DP_S_02_adapter_pattern.py
	3	Decorator	Structural/DP_S_03_decorator_pattern.py
	4	Proxy	Structural/DP_S_04_proxy_pattern.py
	5	Composite	Structural/DP_S_05_composite_pattern.py
	6	Bridge	Structural/DP_S_06_bridge_pattern.py
	7	Flyweight	Structural/DP_S_07_flyweight_pattern.py
Behavioral	1	Strategy	Behavioral/DP_B_01_strategy_pattern.py
	2	Template Method	Behavioral/DP_B_02_template_method_pattern.py
	3	Observer	Behavioral/DP_B_03_observer_pattern.py
	4	Command	Behavioral/DP_B_04_command_pattern.py
	5	Chain of Responsibility	Behavioral/DP_B_05_chain_of_responsibility_pattern.py
	6	Iterator	Behavioral/DP_B_06_iterator_pattern.py
	7	State	Behavioral/DP_B_07_state_pattern.py
	8	Mediator	Behavioral/DP_B_08_mediator_pattern.py
	9	Visitor	Behavioral/DP_B_09_visitor_pattern.py
	10	Memento	Behavioral/DP_B_10_memento_pattern.py
	11	Interpreter	Behavioral/DP_B_11_interpreter_pattern.py
	12	Null Object	Behavioral/DP_B_12_null_object_pattern.py

All 23 classic Gang of Four patterns + 1 additional behavioral pattern (Null Object).

PSE_135 — Architectural Patterns (5 files)

#	Pattern	File
01	Repository	AP_01_repository.py
02	Dependency Injection	AP_02_dependency_injection.py
03	Unit of Work	AP_03_unit_of_work.py
04	Event Sourcing	AP_04_event_sourcing.py
05	CQRS	AP_05_cqrs.py

PSE_140 — Testing (4 files)

#	File	Topic
01	TS_01_unittest.py	TestCase, setUp, assertions
02	TS_02_pytest.py	pytest syntax, parametrize
03	TS_03_mocking.py	unittest.mock, patch
04	TS_04_fixtures.py	pytest fixtures, scope, teardown

PSE_150 — Standard Library (8 files)

#	File	Topic
01	SL_01_collections.py	defaultdict, Counter, deque, namedtuple
02	SL_02_itertools.py	chain, product, combinations, permutations
03	SL_03_functools.py	reduce, partial, lru_cache, wraps
04	SL_04_datetime.py	date, time, timedelta, strftime
05	SL_05_pathlib.py	Path, glob, suffix, parent
06	SL_06_json.py	dumps, loads, custom encoding
07	SL_07_csv.py	reader, writer, DictReader
08	SL_08_logging.py	levels, handlers, basicConfig

PSE_160 — System Design (17 files)

#	File	Topic
01	SD_01_client_server.py	Client-server architecture
02	SD_02_http_rest.py	HTTP methods, REST API design
03	SD_03_dns.py	DNS resolution, load balancing
04	SD_04_load_balancing.py	Round-robin, least connections
05	SD_05_caching.py	Cache-aside pattern, cache vs DB
06	SD_06_rate_limiting.py	Token bucket, sliding window
07	SD_07_message_queue.py	Pub/sub, task queues
08	SD_08_database_replication.py	Primary-replica, read replicas
09	SD_09_database_indexing.py	B-tree, composite indexes
10	SD_10_sharding.py	Horizontal partitioning, shard keys
11	SD_11_consistent_hashing.py	Hash rings, virtual nodes
12	SD_12_proxy.py	Forward proxy, reverse proxy
13	SD_13_microservices.py	Service decomposition, API gateway
14	SD_14_pub_sub.py	Topics, subscribers, fan-out
15	SD_15_url_shortener.py	Encoding, redirection, analytics
16	SD_16_cdn.py	Edge caching, geographic routing
17	SD_17_cap_theorem.py	Consistency, availability, partition tolerance

PSE_170 — Algorithms (1 file)

#	File	Topic
01	AL_01_big_o.py	O(1), O(log n), O(n), O(n²), space complexity

PSE_180 — CLI Frameworks (3 files)

#	File	Topic
01	CLI_01_argparse.py	argparse, subcommands, argument groups
02	CLI_02_click.py	click decorators, options, groups
03	CLI_03_typer.py	typer with type hints, enums

PSE_190 — Serialization (2 files)

#	File	Topic
01	SER_01_pydantic.py	Pydantic models, validation, serialization
02	SER_02_json_formats.py	json, orjson, yaml, toml, msgpack

PSE_200 — Logging Advanced (2 files)

#	File	Topic
01	LOG_01_structlog.py	Structured logging, JSON output
02	LOG_02_loguru.py	Zero-config logging, rotation, async

PSE_210 — HTTP Client (2 files)

#	File	Topic
01	HTTP_01_httpx.py	httpx sync/async, sessions, streaming
02	HTTP_02_requests.py	requests (legacy reference)

PSE_220 — Database (2 files)

#	File	Topic
01	DB_01_sqlalchemy.py	SQLAlchemy ORM, models, relationships
02	DB_02_sqlite3.py	sqlite3 stdlib, CRUD, transactions

PSE_230 — Web Frameworks (2 files)

#	File	Topic
01	WEB_01_fastapi.py	FastAPI routes, Pydantic, dependencies
02	WEB_02_flask.py	Flask routes, request/response

PSE_240 — Terminal UI (2 files)

#	File	Topic
01	TUI_01_rich.py	Tables, progress bars, syntax highlighting
02	TUI_02_textual.py	TUI apps, widgets, CSS styling

PSE_250 — GUI (1 file)

#	File	Topic
01	GUI_01_tkinter.py	Widgets, layouts, events

PSE_260 — Packaging (2 files)

#	File	Topic
01	PKG_01_pyproject.toml.py	pyproject.toml structure, tool config
02	PKG_02_uv.py	uv package manager commands

PSE_270 — Capstone (1 file)

#	File	Topic
01	CAP_01_api_server.py	Full API with FastAPI + SQLAlchemy + tests

How To Use

Run any example directly with Python:

python PSE_000_Python_Basics/PB_01_variables.py
python PSE_010_Functions/FN_09_decorators.py
python PSE_080_OOP/OOP_04_abstraction.py
python PSE_120_SOLID/SOLID_01_single_responsibility.py
python PSE_130_Design_Patterns/Creational/DP_C_01_singleton_pattern.py
python PSE_135_Architectural_Patterns/AP_04_event_sourcing.py
python PSE_135_Architectural_Patterns/AP_05_cqrs.py
python PSE_160_System_Design/SD_05_caching.py
python PSE_160_System_Design/SD_16_cdn.py
python PSE_110_Concurrency/CC_04_asyncio.py
python PSE_170_Algorithms/AL_01_big_o.py

Most files include:

• a short explanation at the top
• a small implementation of the concept
• a main() function that demonstrates the behavior

The examples are educational simulations. System design examples use in-memory data structures instead of real servers, databases, queues, or network calls so the core idea stays easy to inspect.

Requirements

The project uses only the Python standard library.

The current pyproject.toml requires:

Python >= 3.14

Many examples may also work on earlier Python 3 versions, but the repository is configured for Python 3.14 or newer.

Notes

• This is a learning repo, not a production framework.
• Examples favor clarity over completeness.
• System design examples are simplified models of real-world architectures.
• Folder numbering is for learning order, not Python package naming.
• Number gaps (180+) are reserved for future topics.
• New topics should stay small, runnable, and focused on one concept.

Contributing

Contributions and improvements are welcome. Good additions include:

• clearer explanations
• more focused examples
• missing design patterns
• additional system design topics
• small corrections or naming fixes

License

This repository is provided for educational purposes. See LICENSE for details.