Thanks to Igor who emailed me and made me aware, you can't put pseudo classes in style attributes in HTML. I.e. this does not work:
<a href="#" style="color:pink :hover{color:red}">Sample Link</a>
See for yourself: Sample Link
Note how it does not become red when you hover over the link above.
This is what premailer used to do. Until yesterday.
BEFORE:
>>> from premailer import transform
>>> print transform('''
... <html>
... <style>
... a { color: pink }
... a:hover { color: red }
... </style>
... <a href="#">Sample Link</a>
... </html>
... ''')
<html><head><a href="#" style="{color:pink} :hover{color:red}">Sample Link</a></head></html>
AFTER:
>>> from premailer import transform
>>> print transform('''
... <html>
... <style>
... a { color: pink }
... a:hover { color: red }
... </style>
... <a href="#">Sample Link</a>
... </html>
... ''')
<html><head>
<style>a:hover {color:red}</style>
<a href="#" style="color:pink">Sample Link</a>
</head></html>
That's because the new default is exclude pseudo classes by default.
Thanks Igor for making me aware!