Suppress base_url via attribute

[viernullvier]

Don't prepend base_url to URLs if the tag's attribute 'data-premailer' is set to 'ignore'. Helps with / fixes #140.

[peterbe]

You have me convinced in the Issue that we need to tackle this with an option. However, the PR needs some work. I don't like that the data-premailer="ignore" attribute is still there after premailer has transformed. Also, if someone reads data-premailer="ignore" they might think that the whole tag should be ignored. E.g. if you have

<style>a { color: red }</style>
<a href="tel:+1234" data-premailer="ignore">Call</a>
<a href="/">Home page</a>

...and giving someone sets base_url='http://example.com' to the transform, you might expect this output:

<a href="tel:+1234">Call</a>
<a href="http://example.com/" style="color:red">Home page</a>

which is NOT want we want. We just want the href attribute to be ignored.

Do you have some other ideas about how to annotate and tell premailer to "not touch" an attribute value?

[peterbe]

How about this for a functional idea:

def my_replacer(value, base_url):
      if 'tel:' in value:
         # leave it as is 
         return value
     return urlparse.urljoin(base_url, value)
premailer.transform(html, base_url='http://example.com', base_url_replacer=my_replacer)

[peterbe]

So the problem is that it becomes <a href="http://mybaseurl/tel:+1234">Call</a>, right?
Can't we write a regex that checks the content of the href tag before it does the "insertion" of the base_url?