Adds a remove_unset_properties setting. Squashed commits.

premailer/merge_style.py

@@ -19,7 +19,12 @@ def csstext_to_pairs(csstext):
 csstext_to_pairs._lock = threading.RLock()
 
 
-def merge_styles(inline_style, new_styles, classes):
+def merge_styles(
+        inline_style,
+        new_styles,
+        classes,
+        remove_unset_properties=False
+):
     """
         This will merge all new styles where the order is important
         The last one will override the first
@@ -29,9 +34,12 @@ def merge_styles(inline_style, new_styles, classes):
 
         Args:
             inline_style(str): the old inline style of the element if there
-            is one new_styles: a list of new styles, each element should be
-            a list of tuple classes: a list of classes which maps
-            new_styles, important!
+                is one
+            new_styles: a list of new styles, each element should be
+                a list of tuple
+            classes: a list of classes which maps new_styles, important!
+            remove_unset_properties(bool): Allow us to remove certain CSS
+                properties with rules that set their value to 'unset'
 
         Returns:
             str: the final style
@@ -55,6 +63,13 @@ def merge_styles(inline_style, new_styles, classes):
     normal_styles = []
     pseudo_styles = []
     for pseudoclass, kv in styles.items():
+        if remove_unset_properties:
+            # Remove rules that we were going to have value 'unset' because
+            # they effectively are the same as not saying anything about the
+            # property when inlined
+            kv = dict(
+                (k, v) for (k, v) in kv.items() if not v.lower() == 'unset'
+            )
         if not kv:
             continue
         if pseudoclass:

premailer/premailer.py

@@ -115,7 +115,8 @@ class Premailer(object):
                  cssutils_logging_handler=None,
                  cssutils_logging_level=None,
                  disable_leftover_css=False,
-                 align_floating_images=True):
+                 align_floating_images=True,
+                 remove_unset_properties=True):
         self.html = html
         self.base_url = base_url
         self.preserve_internal_links = preserve_internal_links
@@ -143,6 +144,7 @@ class Premailer(object):
         self.cache_css_parsing = cache_css_parsing
         self.disable_leftover_css = disable_leftover_css
         self.align_floating_images = align_floating_images
+        self.remove_unset_properties = remove_unset_properties
 
         if cssutils_logging_handler:
             cssutils.log.addHandler(cssutils_logging_handler)
@@ -396,9 +398,16 @@ class Premailer(object):
         # crucial when you have a lot of pseudo/classes
         # and a long list of elements
         for _, element in elements.items():
-            final_style = merge_styles(element['item'].attrib.get('style', ''),
-                                       element['style'], element['classes'])
-            element['item'].attrib['style'] = final_style
+            final_style = merge_styles(
+                element['item'].attrib.get('style', ''),
+                element['style'],
+                element['classes'],
+                remove_unset_properties=self.remove_unset_properties,
+            )
+            if final_style:
+                # final style could be empty string because of
+                # remove_unset_properties
+                element['item'].attrib['style'] = final_style
             self._style_to_basic_html_attributes(
                 element['item'],
                 final_style,

premailer/tests/test_premailer.py

@@ -143,6 +143,21 @@ class Tests(unittest.TestCase):
         for each in expect:
             ok_(each in result)
 
+    def test_merge_styles_with_unset(self):
+        inline_style = 'color: red'
+        new = 'font-size: 10px; font-size: unset; font-weight: bold'
+        expect = 'color:red;', 'font-weight:bold'
+        css_new = csstext_to_pairs(new)
+        result = merge_styles(
+            inline_style,
+            [css_new],
+            [''],
+            remove_unset_properties=True,
+        )
+        for each in expect:
+            ok_(each in result)
+        ok_('font-size' not in result)
+
     def test_basic_html(self):
         """test the simplest case"""
 
@@ -2453,3 +2468,36 @@ sheet" type="text/css">
         p = Premailer(html, align_floating_images=True)
         result_html = p.transform()
         compare_html(expect_html, result_html)
+
+    def test_remove_unset_properties(self):
+        html = """<html>
+        <head>
+        <style>
+        div {
+            color: green;
+        }
+        span {
+            color: blue;
+        }
+        span.nocolor {
+            color: unset;
+        }
+        </style>
+        </head>
+        <body>
+        <div class="color"><span class="nocolor"></span></div>
+        </body>
+        </html>"""
+
+        expect_html = """<html>
+        <head>
+        </head>
+        <body>
+        <div style="color:green"><span></span></div>
+        </body>
+        </html>"""
+
+        p = Premailer(html, remove_unset_properties=True)
+        self.assertTrue(p.remove_unset_properties)
+        result_html = p.transform()
+        compare_html(expect_html, result_html)