Added ability to pass in a session_id and instance to the init.

Author: Dale Francum

README.rst

@@ -8,6 +8,7 @@ Usage
 -----
 To use API classes one needs to create a session first by instantiating SfdcSession class and passing login details to the constructor.
 
+One method is to pass in the username, password, and token:
 .. code-block:: python
 
     from sfdclib import SfdcSession
@@ -20,6 +21,22 @@ To use API classes one needs to create a session first by instantiating SfdcSess
     )
     s.login()
 
+A second method, if you've already logged in elsewhere, is to pass in the instance and session_id. This method does not require calling login().
+.. code-block:: python
+
+    from sfdclib import SfdcSession
+
+    s = SfdcSession(
+        'username': None,
+        'password': None,
+        'token': None,
+        'is_sandbox': True,
+        'api_version': "37.0",
+        'session_id': 'thiswillbeaverylongstringofcharactersincludinglettersspacesandsymbols',
+        'instance': 'custom-sf-site.my'
+    )
+    # Notice we are not calling the login() method for this example.
+
 Then create an instance of corresponding API class passing session object.
 
 .. code-block:: python

setup.py

@@ -5,7 +5,7 @@
 
 setup(
     name='sfdclib',
-    version='0.2.15',
+    version='0.2.16',
     author='Andrey Shevtsov',
     author_email='[email protected]',
     packages=['sfdclib'],

sfdclib/session.py

@@ -28,15 +28,16 @@ class SfdcSession(Session):
 
     def __init__(
             self, username=None, password=None, token=None,
-            is_sandbox=False, api_version=_DEFAULT_API_VERSION):
+            is_sandbox=False, api_version=_DEFAULT_API_VERSION,
+            session_id=None, instance=None):
         super(SfdcSession, self).__init__()
         self._username = username
         self._password = password
         self._token = token
         self._is_sandbox = is_sandbox
         self._api_version = api_version
-        self._session_id = None
-        self._instance = None
+        self._session_id = session_id
+        self._instance = instance
 
     def login(self):
         url = self.construct_url(self.get_soap_api_uri())