Enhance PDF Export: Add CJK LaTeX Template Support

by Alex Johnson 51 views

The Challenge of CJK Text in PDF Exports

For many users, especially those working with East Asian languages like Chinese, Japanese, or Korean (CJK), generating PDF reports from Jupyter notebooks can present a unique set of challenges. While nbconvert has made significant strides in Unicode support by switching to XeTeX, a common hurdle remains: out-of-the-box PDF export often fails to render CJK characters correctly. This means that instead of seeing your beautifully crafted Chinese or Japanese text, you're met with blank spaces or the dreaded "tofu" (â–¡) boxes. This issue, first highlighted in issue #409 back in 2016, persists and requires manual intervention for CJK users. The core problem lies in the default LaTeX template not being pre-configured with the necessary packages and font setups to handle these complex scripts.

Understanding the Current Workarounds for CJK Users

Currently, users needing CJK support in their nbconvert PDFs typically resort to custom LaTeX templates. This often involves manually adding specific LaTeX packages like fontspec and xeCJK, along with instructions to use a CJK font. A common snippet that users might find on blogs or forums looks something like this, embedded within a custom template file:

\usepackage{fontspec}
\usepackage{xeCJK}
\setmainfont{Latin Modern Roman} % For Latin scripts
\setCJKmainfont{Noto Sans CJK SC} % For Chinese characters

To utilize this, users would then execute nbconvert with a command like jupyter nbconvert notebook.ipynb --to pdf --template <your_custom_cjk_template>. While this workaround is effective as long as the necessary TeX distributions (like texlive-xetex) and the specified CJK font are installed on the system, it's not an intuitive or easily discoverable solution. It relies on users piecing together information from disparate sources, which isn't ideal for a seamless user experience. The lack of an official, built-in solution means many CJK users might be struggling with PDF generation or settling for incomplete reports.

A Proposal for an Official CJK-Friendly LaTeX Template

To address this gap and improve the nbconvert experience for CJK users, a proposal has been put forth to include an optional, CJK-capable LaTeX template directly within the nbconvert project. The idea is not to alter the default template, which could potentially break existing workflows for non-CJK users, but rather to provide an alternative that users can opt into. This optional template, perhaps named latex_cjk or something similar, would extend the existing default template and integrate the necessary configurations for CJK text rendering. Specifically, it would include fontspec, xeCJK, and a mechanism to specify a CJK font, such as \setCJKmainfont{...}.

This approach offers several advantages. Firstly, it makes CJK support readily available without requiring users to hunt for custom solutions. Secondly, it maintains the stability of the default export for the majority of users. Thirdly, by including it officially, the project can ensure better maintenance and consistency. The implementation would ideally leverage nbconvert's modern templating system, likely using .tex.j2 files and conf.json for configuration, ensuring it aligns with the project's internal standards. This would allow for features like configurable CJK font names, either through template variables or configuration settings, making the template more flexible and user-friendly. Imagine being able to simply run jupyter nbconvert notebook.ipynb --to pdf --template latex_cjk and have your CJK text render perfectly – that's the goal.

Enhancing Documentation for CJK Users

Complementing the inclusion of an optional CJK-friendly LaTeX template, a crucial step towards making this feature accessible and understandable is to enhance the nbconvert documentation. A dedicated section, perhaps titled "Using nbconvert with CJK Languages," would be invaluable. This documentation should clearly outline how CJK users can leverage the new template, providing straightforward instructions.

Key information to include would be:

  • How to use the template: A simple command example like jupyter nbconvert notebook.ipynb --to pdf --template latex_cjk. This immediately tells users how to activate the feature.
  • Configuring CJK fonts: Explanation on how users can specify their preferred CJK font. This could involve using template variables or configuration options, allowing for customization based on system availability and personal preference. For instance, mentioning that users might need to install fonts like Noto Sans CJK or others depending on their operating system and distribution.
  • Required TeX packages: A clear list of the additional TeX Live packages that users might need to install to ensure full CJK support. This could include packages such as texlive-xetex (essential for XeTeX), texlive-lang-chinese, texlive-lang-japanese, and texlive-lang-korean, depending on the specific CJK language being used. Providing these details upfront can prevent common installation-related issues.

By offering clear, concise documentation, nbconvert can empower CJK users to generate professional-looking PDF reports with confidence. This not only improves the user experience but also solidifies nbconvert as a versatile tool for a global audience. The inclusion of a small, dedicated test notebook within the repository would also be beneficial, serving as a practical example and a regression test for future updates. This comprehensive approach ensures that the new feature is not only present but also discoverable and easy to use for everyone.

Next Steps and Community Involvement

To move forward with this proposal, the next logical step involves engaging with the nbconvert maintainers to gauge their openness to such a contribution. Key questions for the team include:

  • Existing Efforts: Is there any ongoing or planned work related to CJK PDF support that might overlap with this proposal? Understanding the current roadmap is crucial for effective contribution.
  • Acceptance of a PR: Would the project be receptive to a Pull Request (PR) that introduces an optional latex_cjk template, includes a basic CJK test notebook, and adds the necessary documentation? This clarifies the project's willingness to accept this type of enhancement.
  • Design Preferences: Are there any specific preferences regarding the naming convention and location of the new template? Additionally, any guidance on which CJK fonts to use as examples (e.g., Noto Sans CJK versus relying on system defaults) would be helpful for implementation.

If the direction outlined here is deemed reasonable and aligns with the project's goals, the next step would be for the proposer to prepare and submit a PR. This PR would aim to implement the optional template, add a relevant test case, and incorporate the suggested documentation updates. Feedback from the maintainers during the PR review process would then guide further iterations and refinements. This collaborative approach ensures that the contribution meets the project's standards and effectively addresses the needs of the CJK user community. The ultimate goal is to make nbconvert a more inclusive and powerful tool for all users, regardless of the language they use in their notebooks.

This initiative seeks to significantly improve the usability of nbconvert for a substantial user base. By providing an official, easy-to-use solution for CJK text rendering in PDF exports, the project can enhance its global appeal and user satisfaction.

For further information on LaTeX and advanced PDF customization, you can refer to the Official LaTeX Project Companion and the XeTeX documentation.