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Merge pull request #563 from realpython/structural-pattern-matching
Materials for Structural Pattern Matching: Initial Commit
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‎structural-pattern-matching/README.md

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# Structural Pattern Matching in Python
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This folder contains the code samples for the Real Python tutorial [Structural Pattern Matching in Python](https://realpython.com/structural-pattern-matching/).
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## Installation
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Create and activate a virtual environment:
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```sh
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$ python -m venv venv/
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$ source venv/bin/activate
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```
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Install the required third-party dependencies:
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```sh
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(venv) $ python -m pip install -r requirements.txt
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```

‎structural-pattern-matching/fetcher.py

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from http.client import HTTPConnection, HTTPResponse, HTTPSConnection
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from sys import stderr
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from urllib.parse import ParseResult, urlparse
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def fetch(url):
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print 8000 (f"Fetching URL: {url}", file=stderr)
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connection = make_connection(url)
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try:
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connection.request("GET", "/")
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match connection.getresponse():
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case HTTPResponse(status=code) if code >= 400:
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raise ValueError("Failed to fetch URL")
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case HTTPResponse(status=code) as resp if (
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code >= 300 and (redirect := resp.getheader("Location"))
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):
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return fetch(redirect)
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case HTTPResponse(status=code) as resp if code >= 200:
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return resp.read()
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case _:
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raise ValueError("Unexpected response")
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finally:
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connection.close()
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def make_connection(url):
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match urlparse(url):
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case ParseResult("http", netloc=host):
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return HTTPConnection(host)
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case ParseResult("https", netloc=host):
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return HTTPSConnection(host)
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case _:
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raise ValueError("Unsupported URL scheme")
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if __name__ == "__main__":
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fetch("http://realpython.com/")

‎structural-pattern-matching/guessing_game.py

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import random
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MIN, MAX = 1, 100
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MAX_TRIES = 5
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PROMPT_1 = f"\N{mage} Guess a number between {MIN} and {MAX}: "
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PROMPT_2 = "\N{mage} Try again: "
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BYE = "Bye \N{waving hand sign}"
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def main():
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print("Welcome to the game! Type 'q' or 'quit' to exit.")
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while True:
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play_game()
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if not want_again():
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bye()
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def play_game():
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drawn_number = random.randint(MIN, MAX)
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num_tries = MAX_TRIES
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prompt = PROMPT_1
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while num_tries > 0:
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match input(prompt):
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case command if command.lower() in ("q", "quit"):
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bye()
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case user_input:
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try:
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user_number = int(user_input)
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except ValueError:
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print("That's not a number!")
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else:
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match user_number:
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case number if number < drawn_number:
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num_tries -= 1
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prompt = PROMPT_2
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print(f"Too low! {num_tries} tries left.")
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case number if number > drawn_number:
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num_tries -= 1
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prompt = PROMPT_2
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print(f"Too high! {num_tries} tries left.")
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case _:
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print("You won \N{party popper}")
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return
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print("You lost \N{pensive face}")
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def want_again():
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while True:
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match input("Do you want to play again? [Y/N] ").lower():
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case "y":
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return True
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case "n":
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return False
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def bye():
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print(BYE)
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exit()
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if __name__ == "__main__":
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try:
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main()
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except (KeyboardInterrupt, EOFError):
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print()
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bye()

‎structural-pattern-matching/interpreter.py

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import sys
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def interpret(code, num_bytes=2**10):
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stack, brackets = [], {}
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for i, instruction in enumerate(code):
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match instruction:
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case "[":
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stack.append(i)
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case "]":
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brackets[i], brackets[j] = (j := stack.pop()), i
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memory = bytearray(num_bytes)
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pointer = ip = 0
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while ip < len(code):
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match code[ip]:
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case ">":
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pointer += 1
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case "<":
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pointer -= 1
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case "+":
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memory[pointer] += 1
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case "-":
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memory[pointer] -= 1
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case ".":
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print(chr(memory[pointer]), end="")
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case ",":
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memory[pointer] = ord(sys.stdin.buffer.read(1))
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case "[" if memory[pointer] == 0:
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ip = brackets[ip]
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case "]" if memory[pointer] != 0:
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ip = brackets[ip]
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ip += 1
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if __name__ == "__main__":
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interpret(
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"""
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+++++++++++[>++++++>+++++++++>++++++++>++++>+++>+<<<<<<-]>+++
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+++.>++.+++++++..+++.>>.>-.<<-.<.+++.------.--------.>>>+.>-.
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"""
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)

‎structural-pattern-matching/issue_comments.py

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import json
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import urllib.request
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from dataclasses import dataclass
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from rich.console import Console
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from rich.markdown import Markdown
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from rich.panel import Panel
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@dataclass
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class Comment:
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when: str
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body: str
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url: str
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user: str
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user_url: str
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issue_title: str
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@property
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def footer(self):
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return (
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f"Comment by [{self.user}]({self.user_url})"
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f" on [{self.when}]({self.url})"
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)
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def render(self):
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return Panel(
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Markdown(f"{self.body}\n\n---\n_{self.footer}_"),
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title=self.issue_title,
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padding=1,
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)
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def fetch_github_events(org, repo):
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url = f"https://api.github.com/repos/{org}/{repo}/events"
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with urllib.request.urlopen(url) as response:
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return json.loads(response.read())
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def filter_comments(events):
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for event in events:
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match event:
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case {
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"type": "IssueCommentEvent",
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"created_at": when,
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"actor": {
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"display_login": user,
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},
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"payload": {
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"action": "created",
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"issue": {
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"state": "open",
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"title": issue_title,
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},
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"comment": {
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"body": body,
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"html_url": url,
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"user": {
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"html_url": user_url,
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},
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},
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},
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}:
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yield Comment(when, body, url, user, user_url, issue_title)
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def main():
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console = Console()
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events = fetch_github_events("python", "cpython")
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for comment in filter_comments(events):
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console.clear()
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console.print(comment.render())
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console.input("\nPress [b]ENTER[/b] for the next comment...")
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if __name__ == "__main__":
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main()

‎structural-pattern-matching/optimizer.py

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import ast
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import inspect
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import textwrap
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def main():
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source_code = inspect.getsource(sample_function)
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source_tree = ast.parse(source_code)
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target_tree = optimize(source_tree)
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target_code = ast.unparse(target_tree)
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print("Before:")
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print(ast.dump(source_tree))
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print(textwrap.indent(source_code, "| "))
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print("After:")
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print(ast.dump(target_tree))
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print(textwrap.indent(target_code, "| "))
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def sample_function():
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return 40 + 2
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def optimize(node):
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match node:
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case ast.Module(body, type_ignores):
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return ast.Module(
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[optimize(child) for child in body], type_ignores
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)
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case ast.FunctionDef():
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return ast.FunctionDef(
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name=node.name,
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args=node.args,
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body=[optimize(child) for child in node.body],
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decorator_list=node.decorator_list,
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returns=node.returns,
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type_comment=node.type_comment,
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type_params=node.type_params,
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lineno=node.lineno,
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)
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case ast.Return(value):
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return ast.Return(value=optimize(value))
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case ast.BinOp(ast.Constant(left), op, ast.Constant(right)):
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match op:
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case ast.Add():
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return ast.Constant(left + right)
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case ast.Sub():
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return ast.Constant(left - right)
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case _:
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return node
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case _:
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return node
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if __name__ == "__main__":
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main()

‎structural-pattern-matching/repl.py

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import ast
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import sys
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import traceback
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PROMPT = "\N{snake} "
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COMMANDS = ("help", "exit", "quit")
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def main():
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print('Type "help" for more information, "exit" or "quit" to finish.')
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while True:
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try:
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match input(PROMPT):
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case command if command.lower() in COMMANDS:
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match command.lower():
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case "help":
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print(f"Python {sys.version}")
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case "exit" | "quit":
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break
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case expression if valid(expression, "eval"):
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_ = eval(expression)
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if _ is not None:
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print(_)
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case statement if valid(statement, "exec"):
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exec(statement)
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case _:
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print("Please type a command or valid Python")
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except KeyboardInterrupt:
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print("\nKeyboardInterrupt")
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except EOFError:
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print()
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exit()
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except Exception:
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traceback.print_exc(file=sys.stdout)
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def valid(code, mode):
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try:
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ast.parse(code, mode=mode)
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return True
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except SyntaxError:
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return False
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if __name__ == "__main__":
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main()

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