Fast CSS inlining written in Rust

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Project description

css_inline

Build PyPI Python versions License

Blazing-fast CSS inlining for Python implemented with Mozilla's Servo project components.

Features:

  • Removing style tags after inlining;
  • Resolving external stylesheets (including local files);
  • Control if style tags should be processed;
  • Out-of-document CSS to inline;
  • Inlining multiple documents in parallel (via Rust-level threads)

The project supports CSS Syntax Level 3.

Installation

To install css_inline via pip run the following command:

pip install css_inline

Pre-compiled wheels for most popular platforms are provided. If your platform is not in the support table below, you will need a Rust compiler to build this package from source. The minimum supported Rust version is 1.54.

Usage

To inline CSS in a HTML document:

import css_inline

HTML = """<html>
<head>
    <title>Test</title>
    <style>h1 { color:blue; }</style>
</head>
<body>
    <h1>Big Text</h1>
</body>
</html>"""

inlined = css_inline.inline(HTML)
# HTML becomes this:
#
# <html>
# <head>
#    <title>Test</title>
#    <style>h1 { color:blue; }</style>
# </head>
# <body>
#     <h1 style="color:blue;">Big Text</h1>
# </body>
# </html>

If you want to inline many HTML documents, you can utilize inline_many that processes the input in parallel.

import css_inline

css_inline.inline_many(["<...>", "<...>"])

inline_many will use Rust-level threads; thus, you can expect it's running faster than css_inline.inline via Python's multiprocessing or threading modules.

For customization options use the CSSInliner class:

import css_inline

inliner = css_inline.CSSInliner(remove_style_tags=True)
inliner.inline("...")

If you'd like to skip CSS inlining for an HTML tag, add data-css-inline="ignore" attribute to it:

<head>
    <title>Test</title>
    <style>h1 { color:blue; }</style>
</head>
<body>
    <!-- The tag below won't receive additional styles -->
    <h1 data-css-inline="ignore">Big Text</h1>
</body>
</html>

This attribute also allows you to skip link and style tags:

<head>
    <title>Test</title>
    <!-- Styles below are ignored -->
    <style data-css-inline="ignore">h1 { color:blue; }</style>
</head>
<body>
    <h1>Big Text</h1>
</body>
</html>

If you'd like to load stylesheets from your filesystem, use the file:// scheme:

import css_inline

# styles/email is relative to the current directory
inliner = css_inline.CSSInliner(base_url="file://styles/email/")
inliner.inline("...")

Standards support & restrictions

css-inline is built on top of kuchiki and cssparser and relies on their behavior for HTML / CSS parsing and serialization. Notably:

  • Only HTML 5, XHTML is not supported;
  • Only CSS 3;
  • Only UTF-8 for string representation. Other document encodings are not yet supported.

If you'd like to work around some XHTML compatibility issues like closing empty tags (<hr> vs. <hr/>), you can use the following snippet that involves lxml:

import css_inline
from lxml import html, etree

document = "..."  # Your HTML document
inlined = css_inline.inline(document)
tree = html.fromstring(inlined)
inlined = etree.tostring(tree).decode(encoding="utf-8")

Performance

Due to the usage of efficient tooling from Mozilla's Servo project (html5ever, rust-cssparser and others) this library has excellent performance characteristics. In comparison with other Python projects, it is usually >10x faster than the nearest alternative.

For inlining CSS in the html document from the Usage section above there is the following breakdown in the benchmarks:

  • css_inline 0.8.2 - 22.42 us
  • premailer 3.10.0 - 332.02 us (x14.81)
  • toronado 0.1.0 - 1.59 ms (x71.17)
  • inlinestyler 0.2.5 - 2.35 ms (x105.07)
  • pynliner 0.8.0 - 2.79 ms (x124.80)

Realistic email 1:

  • css_inline 0.8.2 - 487.75 us
  • premailer 3.10.0 - 3.92 ms (x8.05)
  • toronado 0.1.0 - 52.09 ms (x106.81)
  • inlinestyler 0.2.5 - 81.17 ms (x166.43)
  • pynliner 0.8.0 - 128.81 ms (x264.1)

Realistic email 2:

  • css_inline 0.8.2 - 386.64 us
  • premailer 3.10.0 - 4.82 ms (x12.47)
  • toronado 0.1.0 - Error: Pseudo-elements are not supported
  • inlinestyler 0.2.5 - 40.80 ms (x105.54)
  • pynliner 0.8.0 - Error: No match was found

You can take a look at the benchmarks' code at benches/bench.py file. The results above were measured with stable rustc 1.64.0, Python 3.10.4, Linux x86_64 on i8700K, and 32GB RAM.

Comparison with other libraries

Besides performance, css-inline differs from other Python libraries for CSS inlining.

  • Generally supports more CSS features than other libraries (for example, toronado and pynliner do not support pseudo-elements);
  • It has fewer configuration options and not as flexible as premailer;
  • Works on fewer platforms than LXML-based libraries (premailer, inlinestyler, toronado, and optionally pynliner);
  • Does not have debug logs yet;
  • Supports only HTML 5.

Python support

css_inline supports CPython 3.7, 3.8, 3.9, 3.10, 3.11 and PyPy 3.7, 3.8, 3.9.

Extra materials

If you want to know how this library was created & how it works internally, you could take a look at these articles:

License

The code in this project is licensed under MIT license. By contributing to css_inline, you agree that your contributions will be licensed under its MIT license.

Project details

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Reason this release was yanked:

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