Comprehensive Python Cheat Sheet: Version Differences, Core Libraries, Advanced Topics, and Code Samples

This document is a detailed collection of Python notes and examples compiled by a developer, covering language differences, useful libraries, advanced concepts, design patterns, and system-level knowledge.

Py2 VS Py3

print becomes a function; in Python 2 it is a keyword.

unicode is default str in Python 3.

Division returns float.

long type removed.

xrange replaced by range.

Support for Chinese identifiers.

Advanced unpacking and * unpacking.

Keyword‑only arguments require name=value.

raise from syntax.

dict.iteritems renamed to items().

yield from for delegating to sub‑generators.

asyncio, async/await native coroutine support.

New modules: enum, mock, ipaddress, concurrent.futures, asyncio, urllib, selector.

Py2/3 Conversion Tools

six module for compatibility.

2to3 tool to convert syntax.

__future__ imports to use upcoming features.

Common Libraries

collections – essential data structures.

heapq – priority queue operations.

itertools – advanced iterator utilities.

contextlib – context manager helpers.

types – includes coroutine support via types.coroutine.

html – HTML escaping and unescaping.

mock – testing mocks.

concurrent.futures – thread and process pools.

asyncio – asynchronous I/O framework.

multiprocessing – Manager, Pipe, Queue, Pool examples.

sys – argv, path, modules, exit.

time – default time functions.

inspect, cProfile, bisect, fnmatch, timeit – various utilities.

Enum Example

<span style="color: #5c6370; font-style: italic;"># 枚举的注意事项</span>
from enum import Enum

class COLOR(Enum):
    YELLOW = 1
    GREEN = 1  # alias, no error
    BLACK = 3
    RED = 4

print(COLOR.GREEN)  # prints COLOR.YELLOW
for i in COLOR:
    print(i)

Concurrency and Async

Examples of using ThreadPoolExecutor, asyncio futures, tasks, loops, and coroutine locks.

import asyncio
future = asyncio.ensure_future(coro)
loop.run_until_complete(future)

Multiprocessing Examples

from multiprocessing import Manager, Process

def add_data(p_dict, key, value):
    p_dict[key] = value

if __name__ == "__main__":
    progress_dict = Manager().dict()
    p1 = Process(target=add_data, args=(progress_dict, "bobby1", 22))
    p2 = Process(target=add_data, args=(progress_dict, "bobby2", 23))
    p1.start(); p2.start()
    p1.join(); p2.join()
    print(progress_dict)

Design Patterns

Singleton, Factory, Builder examples in Python.

# Singleton via __new__
class Single:
    def __new__(cls, *args, **kwargs):
        if not hasattr(cls, "_instance"):
            cls._instance = super().__new__(cls)
        return cls._instance

Database Topics

MySQL index evolution, clustering, InnoDB vs MyISAM, index usage rules, aggregation, and query optimization tips.

Redis Overview

High performance due to in‑memory, single‑threaded design.

Data types: strings, lists, hashes, sets, sorted sets, bitmaps, hyperloglog.

Persistence: RDB snapshots and AOF logs.

Transactions via MULTI/EXEC, WATCH.

Distributed lock pattern using SETNX with expiration.

Common issues: cache avalanche, penetration, snowball, pre‑warming, degradation.

Linux and System Knowledge

IO models: select, poll, epoll, blocking, non‑blocking, signal‑driven, async.

Process management: kill -9 vs -15.

Memory management: paging vs segmentation.

Monitoring tools: top, free.

Algorithms and Data Structures

Implementations of quick sort, merge sort, heap sort, binary search, stack, queue, linked list operations, and tree manipulations.

def quick_sort(arr):
    if len(arr) < 2:
        return arr
    pivot = arr[0]
    left = [x for x in arr[1:] if x < pivot]
    right = [x for x in arr[1:] if x >= pivot]
    return quick_sort(left) + [pivot] + quick_sort(right)

Interview Preparation

Advanced questions on database design, distributed locks, short‑URL services, seckill systems, and algorithmic challenges.

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