fix alias

Author: lharries

example.py

@@ -41,9 +41,9 @@
 
 print(posthog.feature_enabled("beta-feature", "distinct_id"))
 
-# # Alias a previous distinct id with a new one
+# Add an alias_id to a distinct_id
 
-posthog.alias("distinct_id", "new_distinct_id")
+posthog.alias("distinct_id", "alias_id")
 
 posthog.capture("new_distinct_id", "event2", {"property1": "value", "property2": "value"})
 posthog.capture(

posthog/__init__.py

@@ -199,8 +199,8 @@ def group_identify(
 
 
 def alias(
-    previous_id,  # type: str,
-    distinct_id,  # type: str,
+    distinct_id,  # type: str
+    previous_id,  # type: str
     context=None,  # type: Optional[Dict]
     timestamp=None,  # type: Optional[datetime.datetime]
     uuid=None,  # type: Optional[str]
@@ -214,18 +214,25 @@ def alias(
     The same concept applies for when a user logs in.
 
     An `alias` call requires
-    - `previous distinct id` the unique ID of the user before
-    - `distinct id` the current unique id
+    - `distinct id` the current unique id of the user (normally the id in your database)
+    - `alias distinct id` the alias id you want to attach to the user, such as the anonymous session id or another ID like their email
+
 
     For example:
     ```python
-    posthog.alias('anonymous session id', 'distinct id')
+    posthog.alias('distinct id', 'anonymous session id')
+    ```
+
+    or 
+
+    ```python
+    posthog.alias('distinct id', '[email protected]')
     ```
     """
     _proxy(
         "alias",
-        previous_id=previous_id,
         distinct_id=distinct_id,
+        previous_id=previous_id,
         context=context,
         timestamp=timestamp,
         uuid=uuid,

posthog/client.py

@@ -241,21 +241,21 @@ def group_identify(self, group_type=None, group_key=None, properties=None, conte
 
         return self._enqueue(msg)
 
-    def alias(self, previous_id=None, distinct_id=None, context=None, timestamp=None, uuid=None):
+    def alias(self, distinct_id=None, previous_id=None, context=None, timestamp=None, uuid=None):
         context = context or {}
 
         require("previous_id", previous_id, ID_TYPES)
         require("distinct_id", distinct_id, ID_TYPES)
 
         msg = {
             "properties": {
-                "distinct_id": previous_id,
-                "alias": distinct_id,
+                "distinct_id": distinct_id,
+                "alias": previous_id,
             },
             "timestamp": timestamp,
             "context": context,
             "event": "$create_alias",
-            "distinct_id": previous_id,
+            "distinct_id": distinct_id,
         }
 
         return self._enqueue(msg)