Non-optimized script but working

main.py

+import time
+t1 = time.time()
+
 from configparser import ConfigParser
 
 from re2oapi import Re2oAPIClient
@@ -10,6 +13,38 @@ password = config.get('Re2o', 'password')
 username = config.get('Re2o', 'username')
 
 api_client = Re2oAPIClient(hostname, username, password)
+domains = api_client.list_domains()
+
 extensions = api_client.list_extensions()
 
-print(len(extensions))
+for extension in extensions:
+
+    host_mac_ip = []
+    for domain in domains:
+        if domain['interface_parent'] is not None and \
+                api_client.get(domain['extension'])['name'] == extension['name']:
+            interface = api_client.get(domain['interface_parent'])
+            if interface['active']:
+                host_mac_ip.append((
+                    domain['name'],
+                    interface['mac_address'],
+                    api_client.get(interface['ipv4'])['ipv4']
+                ))
+    
+    template = ("host {hostname}{extension} {{\n"
+                "    hardware ethernet {mac};\n"
+                "    fixed-address {ipv4};\n"
+                "}}")
+    
+    dhcp_leases_content = '\n\n'.join(template.format(
+            hostname=hostname,
+            extension=extension['name'],
+            mac=mac,
+            ipv4=ip
+        ) for hostname, mac, ip in host_mac_ip)
+    
+    filename = 'dhcp-{extension}.list'.format(extension=extension['name'][1:])
+    with open(filename, 'w+') as f:
+        f.write(dhcp_leases_content)
+
+print(time.time() - t1)