Rewrite of Parser class because it was fucked up. Now there's no problems with inheritance and its subclasses now more pleasant to write. ThreadNotFoundError now has a reason field.

scrapthechan/parser.py

@@ -4,7 +4,7 @@ from itertools import chain
 from json import loads
 from re import findall, match
 from typing import List, Optional
-from urllib.request import urlopen, Request
+from urllib.request import urlopen, Request, HTTPError
 
 from scrapthechan import USER_AGENT
 from scrapthechan.fileinfo import FileInfo
@@ -14,7 +14,12 @@ __all__ = ["Parser", "ThreadNotFoundError"]
 
 
 class ThreadNotFoundError(Exception):
-	pass
+	def __init__(self, reason: str = ""):
+		self._reason = reason
+
+	@property
+	def reason(self) -> str:
+		return self._reason
 
 
 class Parser:
@@ -25,28 +30,42 @@ class Parser:
 
 	Arguments:
 		board      -- is a name of a board on an image board;
-		thread     -- is a name of a thread inside a board;
-		posts      -- is a list of posts in form of dictionaries exported from a JSON;
+		thread     -- is an id of a thread inside a board;
 		skip_posts -- number of posts to skip.
 
 	All the extracted files will be stored as the `FileInfo` objects."""
-	__url_thread_json: str = "https://example.org/{board}/{thread}.json"
-	__url_file_link: str = None
 
-	def __init__(self, board: str, thread: str, posts: List[dict],
+	def __init__(self, board: str, thread: str,
 				 skip_posts: Optional[int] = None) -> None:
-		self._board = board
-		self._thread = thread
-		self._op_post = posts[0]
-		if not skip_posts is None:
-			posts = posts[skip_posts:]
+
+		self._board: str = board
+		self._thread: str = thread
+		self._posts = self._extract_posts_list(self._get_json())
+		self._op_post: dict = self._posts[0]
+		self._posts = self._posts[skip_posts:] if not skip_posts is None else self._posts
 		self._files = list(chain.from_iterable(filter(None, \
-			map(self._parse_post, posts))))
+			map(self._parse_post, self._posts))))
+
+	@property
+	def json_thread_url(self) -> str:
+		raise NotImplementedError
+
+	@property
+	def file_base_url(self) -> str:
+		raise NotImplementedError
+	
+	@property
+	def subject_field(self) -> str:
+		return "sub"
+	
+	@property
+	def comment_field(self) -> str:
+		return "com"
 
 	@property
 	def imageboard(self) -> str:
 		"""Returns image board's name."""
-		return NotImplementedError
+		raise NotImplementedError
 
 	@property
 	def board(self) -> str:
@@ -62,22 +81,40 @@ class Parser:
 	def op(self) -> str:
 		"""Returns OP's post as combination of subject and comment separated
 		by a new line."""
-		raise NotImplementedError
+		op = ""
+		if self.subject_field in self._op_post:
+			op = f"{self._op_post[self.subject_field]}\n"
+		if self.comment_field in self._op_post:
+			op += self._op_post[self.comment_field]
+		return op if not op == "" else None
 
 	@property
 	def files(self) -> List[FileInfo]:
 		"""Returns a list of retrieved files as `FileInfo` objects."""
 		return self._files
 
-	def _get_json(self, thread_url: str) -> dict:
-		"""Gets JSON version of a thread and converts it in a dictionary."""
+	def _extract_posts_list(self, lst: List) -> List[dict]:
+		"""This method must be overridden in child classes where you specify
+		a path in a JSON document where posts are stored. E.g., on 4chan this is
+		['posts'], and on 2ch.hk it's ['threads'][0]['posts']."""
+		return lst
+
+	def _get_json(self) -> dict:
+		"""Retrieves a JSON representation of a thread and converts it in
+		a dictionary."""
 		try:
+			thread_url = self.json_thread_url.format(board=self._board, \
+				thread=self._thread)
 			req = Request(thread_url, headers={'User-Agent': USER_AGENT})
 			with urlopen(req) as url:
 				return loads(url.read().decode('utf-8'))
-		except:
-			raise ThreadNotFoundError
+		except HTTPError as e:
+			raise ThreadNotFoundError(str(e))
+		except Exception as e:
+			raise e
 
-	def _parse_post(self, post: dict) -> List[FileInfo]:
-		"""Parses a single post and extracts files into `FileInfo` object."""
+	def _parse_post(self, post: dict) -> Optional[List[FileInfo]]:
+		"""Parses a single post and extracts files into `FileInfo` object.
+		Single object is wrapped in a list for convenient insertion into
+		a list."""
 		raise NotImplementedError