import configparser from abc import ABC, abstractmethod from contextlib import asynccontextmanager from pathlib import Path # TODO In Python 3.9 and above, AsyncContextManager is deprecated from typing import AsyncContextManager, AsyncIterator, Optional from rich.markup import escape from .conductor import ProgressBar, TerminalConductor from .limiter import Limiter from .transformer import RuleParseException, Transformer class CrawlerLoadException(Exception): pass class Crawler(ABC): def __init__(self, name: str, section: configparser.SectionProxy) -> None: """ Initialize a crawler from its name and its section in the config file. If you are writing your own constructor for your own crawler, make sure to call this constructor first (via super().__init__). May throw a CrawlerLoadException. """ self.name = name self._conductor = TerminalConductor() self._limiter = Limiter() try: self._transformer = Transformer(section.get("transform", "")) except RuleParseException as e: e.pretty_print() raise CrawlerLoadException() # output_dir = Path(section.get("output_dir", name)) def print(self, text: str) -> None: """ Print rich markup to the terminal. Crawlers *must* use this function to print things unless they are holding an exclusive output context manager! Be careful to escape all user-supplied strings. """ self._conductor.print(text) def exclusive_output(self) -> AsyncContextManager[None]: """ Acquire exclusive rights™ to the terminal output. While this context manager is held, output such as printing and progress bars from other threads is suspended and the current thread may do whatever it wants with the terminal. However, it must return the terminal to its original state before exiting the context manager. No two threads can hold this context manager at the same time. Useful for password or confirmation prompts as well as running other programs while crawling (e. g. to get certain credentials). """ return self._conductor.exclusive_output() @asynccontextmanager async def progress_bar( self, desc: str, total: Optional[int] = None, ) -> AsyncIterator[ProgressBar]: async with self._limiter.limit(): with self._conductor.progress_bar(desc, total=total) as bar: yield bar def crawl_bar(self, path: Path) -> AsyncContextManager[ProgressBar]: pathstr = escape(str(path)) desc = f"[bold magenta]Crawling[/bold magenta] {pathstr}" return self.progress_bar(desc) def download_bar( self, path: Path, size: int, ) -> AsyncContextManager[ProgressBar]: pathstr = escape(str(path)) desc = f"[bold green]Downloading[/bold green] {pathstr}" return self.progress_bar(desc, total=size) async def run(self) -> None: """ Start the crawling process. Call this function if you want to use a crawler. """ async with self._conductor: await self.crawl() @abstractmethod async def crawl(self) -> None: """ Overwrite this function if you are writing a crawler. This function must not return before all crawling is complete. To crawl multiple things concurrently, asyncio.gather can be used. """ pass