refactor

services.py

@@ -0,0 +1,9 @@
+import re
+
+
+async def check_lnaddress_format(username: str) -> bool:
+    # check username complies with lnaddress specification
+    if not re.match("^[a-z0-9-_.]{3,15}$", username):
+        assert False, "Only letters a-z0-9-_. allowed, min 3 and max 15 characters!"
+        return
+    return True