added age restriction error

pytube/__main__.py

@@ -18,6 +18,7 @@ from pytube import request
 from pytube import Stream
 from pytube import StreamQuery
 from pytube.compat import parse_qsl
+from pytube.exceptions import AgeRestrictionError
 from pytube.helpers import apply_mixin
 
 
@@ -125,6 +126,8 @@ class YouTube(object):
 
         """
         self.watch_html = request.get(url=self.watch_url)
+        if extract.is_age_restricted(self.watch_html):
+            raise AgeRestrictionError('Content is age restricted')
         self.vid_info_url = extract.video_info_url(
             video_id=self.video_id,
             watch_url=self.watch_url,

pytube/exceptions.py

@@ -59,3 +59,7 @@ class ExtractError(PytubeError):
 
 class RegexMatchError(ExtractError):
     """Regex pattern did not return any matches."""
+
+
+class AgeRestrictionError(ExtractError):
+    """Content is age restricted."""

pytube/extract.py

@@ -5,9 +5,26 @@ from collections import OrderedDict
 
 from pytube.compat import quote
 from pytube.compat import urlencode
+from pytube.exceptions import RegexMatchError
 from pytube.helpers import regex_search
 
 
+def is_age_restricted(watch_html):
+    """Check if content is age restricted.
+
+    :param str watch_html:
+        The html contents of the watch page.
+    :rtype: bool
+    :returns:
+        Whether or not the content is age restricted.
+    """
+    try:
+        regex_search(r'og:restrictions:age', watch_html, group=0)
+    except RegexMatchError:
+        return False
+    return True
+
+
 def video_id(url):
     """Extract the ``video_id`` from a YouTube url.
 
@@ -50,8 +67,7 @@ def video_info_url(video_id, watch_url, watch_html):
     """
     # I'm not entirely sure what ``t`` represents. Looks to represent a
     # boolean.
-    pattern = r'\W[\'"]?t[\'"]?: ?[\'"](.+?)[\'"]'
-    t = regex_search(pattern, watch_html, group=0)
+    t = regex_search(r'\W[\'"]?t[\'"]?: ?[\'"](.+?)[\'"]', watch_html, group=0)
     # Here we use ``OrderedDict`` so that the output is consistant between
     # Python 2.7+.
     params = OrderedDict([