108 lines
6.5 KiB
ReStructuredText
108 lines
6.5 KiB
ReStructuredText
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Writing an EPUB parser. Part 1
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##############################
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:date: 2022-06-01 01:41
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:author: tyrel
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:category: Python
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:tags: epub, python
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:slug: writing-an-epub-parser-part-1
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:status: published
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Parsing Epubs
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-------------
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Recently I've become frustrated with the experience of reading books on my Kindle Paperwhite. The swipe features, really bother me. I really like MoonReader on Android, but reading on my phone isn't always pleasing. This lead me to look into other hardware. I've been eyeing the BOOX company a while ago, but definitely considering some of their new offerings some time. Until the time I can afford the money to splurge on a new ebook reader, I've decided to start a new project, making my own ebook reader tools!
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I'm starting with EPUBs, as this is one of the easiest to work with. At its core, an EPUB is a zip file with the ``.epub`` extension instead of ``.epub`` with many individual XHTML file chapters inside it. You can read more of how they're structured yourself over at `FILEFORMAT <https://docs.fileformat.com/ebook/epub/>`__.
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The tool I've chosen for reading EPUBs is the Python library `ebooklib <https://pypi.org/project/EbookLib/>`__. This seemed to be a nice lightweight library for reading EPUBs. I also used `DearPyGUI <https://pypi.org/project/dearpygui/>`__ for showing this to the screen, because I figured why not, I like GUI libraries.
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My first task was to find an EPUB file, so I downloaded one from my calibre server. I convert all my ebook files to ``.epub`` and ``.mobi`` on my calibre server so I can access them anywhere I can read my OPDS feed. I chose Throne of Glass (abbreviating to ``TOG.epub`` for rest of post). Loading I launched Python, and ran
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.. code:: console
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>>> from ebooklib import epub
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>>> print(book := epub.read_epub("TOG.epub")
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This returned me a ``<ebooklib.epub.EpubBook object...>`` , seeing I had an EpubBook I ran a ``dir(book)`` and found the properties available to me
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.. code:: python
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['add_author', 'add_item', 'add_metadata', 'add_prefix',
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'bindings',
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'direction',
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'get_item_with_href', 'get_item_with_id', 'get_items',
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'get_items_of_media_type', 'get_items_of_type', 'get_metadata',
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'get_template', 'guide',
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'items',
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'language',
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'metadata',
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'namespaces',
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'pages', 'prefixes',
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'reset',
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'set_cover', 'set_direction', 'set_identifier', 'set_language', 'set_template', 'set_title', 'set_unique_metadata', 'spine',
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'templates', 'title', 'toc',
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'uid',
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'version']
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Of note, the ``get_item_with_X`` entries caught my eye, as well as ``spine``. For my file, ``book.spine`` looks like it gave me a bunch of tuples of ID and a ``"yes"`` string of which I had no Idea what was. I then noticed I had a ``toc`` property, assuming that was a Table of Contents, I printed that out and saw a bunch of ``epub.Link`` objects. This looks like something I could use.
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I will note, at this time I was thinking that this wasn't the direction I wanted to take this project. I really wanted to learn how to parse these things myself, unzip, parse XML, or HTML, etc., but I realized I needed to see someone else's work to even know what is going on. With this "defeat for the evening" admitted, I figured hey, why not at least make SOMETHING, right?" I decided to carry on.
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Seeing I was on at least some track, I opened up PyCharm and made a new Project. First I setup a class called Epub, made a couple of functions for setting things up and ended up with
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.. code:: python
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class Epub:
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def __init__(self, book_path: str) -> None:
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self.contents: ebooklib.epub.EpubBook = epub.read_epub(book_path)
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self.title: str = self.contents.title
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self.toc: List[ebooklib.epub.Link] = self.contents.toc
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I then setup a ``parse_chapters`` file, where I loop through the TOC. Here I went to the definition of ``Link`` and saw I was able to get a ``href`` and a ``title``, I decided my object for chapters would be a dictionary (I'll move to a DataClass later) with ``title`` and ``content``. I remembered from earlier I had a ``get_item_by_href`` so I stored the itext from the TOC's href: ``self.contents.get_item_with_href(link.href).get_content()``. This would later prove to be a bad decision when I opened "The Fold.epub" and realized that a TOC could have a tuple of ``Section`` and ``Link``, not just ``Links``. I ended up storing the item itself, and doing a double loop in the ``parse_chapters`` function to loop if it's a tuple.
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.. code:: python
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def parse_chapters(self) -> None:
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idx = 0
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for _item in self.toc:
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if isinstance(_item, tuple): # In case is section tuple(section, [link, ...])
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for link in _item[1]:
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self._parse_link(idx, link)
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idx += 1
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else:
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self._parse_link(idx, _item)
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idx += 1
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``_parse_link`` simply makes that dictionary of ``title`` and ``item`` I mentioned earlier, with a new ``index`` as I introduced buttons in the DearPyGUI at this time as well.
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.. code:: python
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def _parse_link(self, idx, link) -> None:
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title = link.title
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self.chapters.append(dict(
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index=idx,
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title=title,
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item=self.contents.get_item_with_href(link.href)
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))
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That's really all there is to make an MVP of an EPUB parser. You can use ``BeautifulSoup`` to parse the HTML from the ``get_body_contents()`` calls on items, to make more readable text if you want, but depending on your front end, the HTML may be what you want.
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In my implementation my Epub class keeps track of the currently selected chapter, so this loads from all chapters and sets the ``current_text`` variable.
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.. code:: python
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def load_view(self) -> None:
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item = self.chapters[self.current_index]['item']
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soup = BeautifulSoup(item.get_body_content(), "html.parser")
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text = [para.get_text() for para in soup.find_all("p")]
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self.current_text = "\n".join(text)
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I don't believe any of this code will be useful to anyone outside of my research for now, but it's my first step into writing an EPUB parser myself.
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The DearPyGUI steps are out of scope of this blog post, but here is my `final ebook Reader <https://gist.github.com/tyrelsouza/9c6681850fc00bf5d9f35568faf611d4>`__ which is super inefficient!
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.. figure:: {static}/images/2022-06-01_ebook_reader.png
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:alt: final ebook reader, chapters on left, text on right
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I figure the Dedication page is not *as* copywrited as the rest of the book, so it's fair play showing that much. Sarah J Maas, if you have any issues, I can find another book for my screenshots.
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