Premailer

3.10.0 · active · verified Thu Apr 09

Premailer is a Python library that converts HTML documents containing CSS `<style>` blocks or `<link>` tags into HTML with inline `style` attributes. It leverages `lxml` for parsing and is primarily used for preparing HTML emails, where external stylesheets are often unsupported. The library's latest stable version is 3.10.0 and it maintains an active development status.

Warnings

breaking In version 3.0.0, the default value for the `remove_classes` option changed from `True` to `False`. This means CSS class attributes are now kept in the output HTML by default.
Fix: If you relied on classes being removed, explicitly set `remove_classes=True` in the `Premailer` constructor or `transform` function: `transform(html, remove_classes=True)`.
gotcha Using `premailer.transform` repeatedly in a loop for multiple HTML documents can lead to poor performance, as it creates a new `Premailer` instance with each call.
Fix: For batch processing, instantiate the `Premailer` class once and reuse its `transform` method: `p = Premailer(base_url=MY_BASE_URL); for html_string in get_html_documents(): transformed = p.transform(html_string)`.
gotcha By default, `premailer` attempts to download external stylesheets specified by URLs over the network. This can introduce security risks or performance issues.
Fix: To prevent network requests, set the `allow_network=False` option: `transform(html, allow_network=False)` or `Premailer(html, allow_network=False)`.
gotcha The underlying `cssutils` library, used by `premailer` for CSS parsing, uses Python's standard `logging` module to report issues. By default, these logs might not be captured or visible.
Fix: To capture CSS parsing logs, pass a `cssutils_logging_handler` and `cssutils_logging_level` to the `Premailer` constructor. For example: `import logging; from io import StringIO; mylog = StringIO(); myhandler = logging.StreamHandler(mylog); p = Premailer(..., cssutils_logging_handler=myhandler, cssutils_logging_level=logging.INFO)`.

Install

pip install premailer Install with pip

Imports

transform
```
from premailer import transform
```
A shortcut function for quick, single-document transformations. Not recommended for batch processing due to performance implications.
Premailer
```
from premailer import Premailer
```
The main class for advanced usage and improved performance when processing multiple HTML documents.

Quickstart

This quickstart demonstrates the most basic usage of `premailer` using the `transform` shortcut function. It takes an HTML string with embedded CSS and converts the styles into inline attributes. For more complex scenarios or better performance when processing multiple documents, it is recommended to use the `Premailer` class directly.

from premailer import transform

html_content = """
<html>
<head>
<style type="text/css">
h1 { border:1px solid black }
p { color:red;}
</style>
</head>
<body>
<h1 style="font-weight:bolder">Peter</h1>
<p>Hej</p>
</body>
</html>
"""

# Transform the HTML to inline styles
result_html = transform(html_content)
print(result_html)

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