Add Python example

Author: colinmcdonald22

server-partner-program/purchase-webhooks.mdx

@@ -21,7 +21,7 @@ value should be checked prior to accepting the webhook.
 This value is generated by computing a SHA256 HMAC hash of the body of the webhook. The secret to verify with will be provided to you as part
 of the setup process.
 
-<Tabs items={['Node.js']}>
+<Tabs items={['Node.js', 'Python']}>
   <Tab>
     ```javascript
     const signatureSecret = process.env.LUNAR_CLIENT_WEBHOOK_SECRET;
@@ -33,6 +33,22 @@ of the setup process.
       .digest("hex");
     ```
   </Tab>
+  <Tab>
+    ```python
+    import os
+    import hmac
+    import hashlib
+    
+    signature_secret = os.getenv('LUNAR_CLIENT_WEBHOOK_SECRET')
+    body = ...  # This must be the raw body of the webhook. Parsing as JSON and re-serializing can create differences in whitespace.
+    
+    expected_signature = hmac.new(
+      signature_secret.encode('utf-8'),
+      body.encode('utf-8'),
+      hashlib.sha256
+    ).hexdigest()
+    ```
+  </Tab>
 </Tabs>
 
 ## Webhook Types