[compat] Add compat_xpath

youtube_dl/compat.py

@@ -256,6 +256,16 @@ else:
                 el.text = el.text.decode('utf-8')
         return doc
 
+if sys.version_info < (2, 7):
+    # Here comes the crazy part: In 2.6, if the xpath is a unicode,
+    # .//node does not match if a node is a direct child of . !
+    def compat_xpath(xpath):
+        if isinstance(xpath, compat_str):
+            xpath = xpath.encode('ascii')
+        return xpath
+else:
+    compat_xpath = lambda xpath: xpath
+
 try:
     from urllib.parse import parse_qs as compat_parse_qs
 except ImportError:  # Python 2
@@ -585,6 +595,7 @@ __all__ = [
     'compat_urlparse',
     'compat_urlretrieve',
     'compat_xml_parse_error',
+    'compat_xpath',
     'shlex_quote',
     'subprocess_check_output',
     'workaround_optparse_bug9161',