Created MissingSchema and InvalidSchema which inherits from RequestException and ValueError

requests/exceptions.py

@@ -30,3 +30,9 @@ class URLRequired(RequestException):
 
 class TooManyRedirects(RequestException):
     """Too many redirects."""
+
+class MissingSchema(RequestException, ValueError):
+    """The URL schema (e.g. http or https) is missing."""
+
+class InvalidSchema(RequestException, ValueError):
+    """See defaults.py for valid schemas."""

requests/models.py

@@ -24,7 +24,7 @@ from .packages.urllib3.filepost import encode_multipart_formdata
 from .defaults import SCHEMAS
 from .exceptions import (
     ConnectionError, HTTPError, RequestException, Timeout, TooManyRedirects,
-    URLRequired, SSLError)
+    URLRequired, SSLError, MissingSchema, InvalidSchema)
 from .utils import (
     get_encoding_from_headers, stream_untransfer, guess_filename, requote_uri,
     dict_from_string, stream_decode_response_unicode, get_netrc_auth)
@@ -321,10 +321,10 @@ class Request(object):
         scheme, netloc, path, params, query, fragment = urlparse(url)
 
         if not scheme:
-            raise ValueError("Invalid URL %r: No schema supplied" % url)
+            raise MissingSchema("Invalid URL %r: No schema supplied" % url)
 
         if not scheme in SCHEMAS:
-            raise ValueError("Invalid scheme %r" % scheme)
+            raise InvalidSchema("Invalid scheme %r" % scheme)
 
         netloc = netloc.encode('idna').decode('utf-8')