Version 4.2

Motivated by #92.

instaloader/__init__.py

@@ -1,7 +1,7 @@
 """Download pictures (or videos) along with their captions and other metadata from Instagram."""
 
 
-__version__ = '4.2rc2'
+__version__ = '4.2'
 
 
 try:

instaloader/instaloadercontext.py

@@ -198,7 +198,10 @@ class InstaloaderContext:
         self._sleep()
         login = session.post('https://www.instagram.com/accounts/login/ajax/',
                              data={'password': passwd, 'username': user}, allow_redirects=True)
-        resp_json = login.json()
+        try:
+            resp_json = login.json()
+        except json.decoder.JSONDecodeError:
+            raise ConnectionException("Login error: JSON decode fail, {} - {}.".format(login.status_code, login.reason))
         if resp_json.get('two_factor_required'):
             two_factor_session = copy_session(session)
             two_factor_session.headers.update({'X-CSRFToken': csrf_token})
@@ -207,6 +210,10 @@ class InstaloaderContext:
                                             user,
                                             resp_json['two_factor_info']['two_factor_identifier'])
             raise TwoFactorAuthRequiredException("Login error: two-factor authentication required.")
+        if resp_json.get('checkpoint_url'):
+            raise ConnectionException("Login: Checkpoint required. Point your browser to "
+                                      "https://www.instagram.com{}, "
+                                      "follow the instructions, then retry.".format(resp_json.get('checkpoint_url')))
         if resp_json['status'] != 'ok':
             if 'message' in resp_json:
                 raise ConnectionException("Login error: \"{}\" status, message \"{}\".".format(resp_json['status'],