Extracting publish date (#794)

* Extracting publish date

* Added unit test for .publish_date attribute.

pytube/__main__.py

@@ -262,6 +262,15 @@ class YouTube:
 
         return f"https://img.youtube.com/vi/{self.video_id}/maxresdefault.jpg"
 
+    @property
+    def publish_date(self):
+        """Get the publish date.
+
+        :rtype: datetime
+
+        """
+        return extract.publish_date(self.watch_html)
+
     @property
     def title(self) -> str:
         """Get the video title.

pytube/extract.py

@@ -4,6 +4,7 @@ import json
 import logging
 import re
 from collections import OrderedDict
+from datetime import datetime
 from typing import Any
 from typing import Dict
 from typing import List
@@ -22,6 +23,24 @@ from pytube.helpers import regex_search
 logger = logging.getLogger(__name__)
 
 
+def publish_date(watch_html: str):
+    """Extract publish date
+    :param str watch_html:
+        The html contents of the watch page.
+    :rtype: str
+    :returns:
+        Publish date of the video.
+    """
+    try:
+        result = regex_search(
+            r"(?<=itemprop=\"datePublished\" content=\")\d{4}-\d{2}-\d{2}",
+            watch_html, group=0
+        )
+    except RegexMatchError:
+        return None
+    return datetime.strptime(result, '%Y-%m-%d')
+
+
 def recording_available(watch_html):
     """Check if live stream recording is available.
 

tests/test_extract.py

@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
 """Unit tests for the :module:`extract <extract>` module."""
+from datetime import datetime
 import pytest
 
 from pytube import extract
@@ -64,6 +65,12 @@ def test_recording_available(cipher_signature):
     assert extract.recording_available(cipher_signature.watch_html)
 
 
+def test_publish_date(cipher_signature):
+    expected = datetime(2019, 12, 5)
+    assert cipher_signature.publish_date == expected
+    assert extract.publish_date('') is None
+
+
 def test_not_recording_available(missing_recording):
     assert not extract.recording_available(missing_recording['watch_html'])