Refactor the @rule parsers into their own methods for easier sub-classing

src/tinycss/css21.py

@@ -13,11 +13,12 @@
 from __future__ import unicode_literals
 from itertools import chain, islice
 
-from .decoding import decode
-from .token_data import TokenList
-from .tokenizer import tokenize_grouped
-from .parsing import (strip_whitespace, remove_whitespace, split_on_comma,
-                      validate_value, validate_block, validate_any, ParseError)
+from tinycss.decoding import decode
+from tinycss.token_data import TokenList
+from tinycss.tokenizer import tokenize_grouped
+from tinycss.parsing import (
+    strip_whitespace, remove_whitespace, split_on_comma, validate_value,
+    validate_any, ParseError)
 
 
 #  stylesheet  : [ CDO | CDC | S | statement ]*;
@@ -293,7 +294,6 @@ class ImportRule(object):
                 ' {0.uri}>'.format(self))
 
 
-
 def _remove_at_charset(tokens):
     """Remove any valid @charset at the beggining of a token stream.
 
@@ -328,6 +328,10 @@ class CSS21Parser(object):
 
     """
 
+    def __init__(self):
+        self.at_parsers = {
+            '@' + x:getattr(self, 'parse_%s_rule' % x) for x in ('media', 'page', 'import', 'charset')}
+
     # User API:
 
     def parse_stylesheet_file(self, css_file, protocol_encoding=None,
@@ -507,7 +511,15 @@ class CSS21Parser(object):
             A parsed at-rule
 
         """
-        if rule.at_keyword == '@page':
+        try:
+            parser = self.at_parsers[rule.at_keyword]
+        except KeyError:
+            raise ParseError(rule, 'unknown at-rule in {0} context: {1}'
+                                    .format(context, rule.at_keyword))
+        else:
+            return parser(rule, previous_rules, errors, context)
+
+    def parse_page_rule(self, rule, previous_rules, errors, context):
         if context != 'stylesheet':
             raise ParseError(rule, '@page rule not allowed in ' + context)
         selector, specificity = self.parse_page_selector(rule.head)
@@ -520,7 +532,7 @@ class CSS21Parser(object):
         return PageRule(selector, specificity, declarations, at_rules,
                         rule.line, rule.column)
 
-        elif rule.at_keyword == '@media':
+    def parse_media_rule(self, rule, previous_rules, errors, context):
         if context != 'stylesheet':
             raise ParseError(rule, '@media rule not allowed in ' + context)
         if not rule.head:
@@ -533,7 +545,7 @@ class CSS21Parser(object):
         errors.extend(rule_errors)
         return MediaRule(media, rules, rule.line, rule.column)
 
-        elif rule.at_keyword == '@import':
+    def parse_import_rule(self, rule, previous_rules, errors, context):
         if context != 'stylesheet':
             raise ParseError(rule,
                 '@import rule not allowed in ' + context)
@@ -561,13 +573,9 @@ class CSS21Parser(object):
             raise ParseError(head[-1], "expected ';', got a block")
         return ImportRule(uri, media, rule.line, rule.column)
 
-        elif rule.at_keyword == '@charset':
+    def parse_charset_rule(self, rule, previous_rules, errors, context):
         raise ParseError(rule, 'mis-placed or malformed @charset rule')
 
-        else:
-            raise ParseError(rule, 'unknown at-rule in {0} context: {1}'
-                                    .format(context, rule.at_keyword))
-
     def parse_media(self, tokens):
         """For CSS 2.1, parse a list of media types.
 

src/tinycss/fonts3.py

@@ -26,13 +26,14 @@ class CSSFonts3Parser(CSS21Parser):
 
     ''' Parse @font-face rules from the CSS 3 fonts module '''
 
-    ALLOWED_CONTEXTS = {'stylesheet', '@media', '@page'}
+    ALLOWED_CONTEXTS_FOR_FONT_FACE = {'stylesheet', '@media', '@page'}
 
-    def parse_at_rule(self, rule, previous_rules, errors, context):
-        if rule.at_keyword != '@font-face':
-            return super(CSSFonts3Parser, self).parse_at_rule(
-                rule, previous_rules, errors, context)
-        if context not in self.ALLOWED_CONTEXTS:
+    def __init__(self):
+        super(CSSFonts3Parser, self).__init__()
+        self.at_parsers['@font-face'] = self.parse_font_face_rule
+
+    def parse_font_face_rule(self, rule, previous_rules, errors, context):
+        if context not in self.ALLOWED_CONTEXTS_FOR_FONT_FACE:
             raise ParseError(rule,
                 '@font-face rule not allowed in ' + context)
         if rule.body is None:

src/tinycss/page3.py

@@ -88,7 +88,7 @@ class CSSPage3Parser(CSS21Parser):
 
     """
 
-    PAGE_MARGIN_AT_KEYWORDS = {
+    PAGE_MARGIN_AT_KEYWORDS = (
         '@top-left-corner',
         '@top-left',
         '@top-center',
@@ -105,10 +105,14 @@ class CSSPage3Parser(CSS21Parser):
         '@right-top',
         '@right-middle',
         '@right-bottom',
-    }
+    )
 
-    def parse_at_rule(self, rule, previous_rules, errors, context):
-        if rule.at_keyword in self.PAGE_MARGIN_AT_KEYWORDS:
+    def __init__(self):
+        super(CSSPage3Parser, self).__init__()
+        for x in self.PAGE_MARGIN_AT_KEYWORDS:
+            self.at_parsers[x] = self.parse_page_margin_rule
+
+    def parse_page_margin_rule(self, rule, previous_rules, errors, context):
         if context != '@page':
             raise ParseError(rule,
                 '%s rule not allowed in %s' % (rule.at_keyword, context))
@@ -120,8 +124,6 @@ class CSSPage3Parser(CSS21Parser):
         errors.extend(body_errors)
         return MarginRule(rule.at_keyword, declarations,
                             rule.line, rule.column)
-        return super(CSSPage3Parser, self).parse_at_rule(
-            rule, previous_rules, errors, context)
 
     def parse_page_selector(self, head):
         """Parse an @page selector.