Apply several lints

telethon/sessions/string.py

@@ -25,10 +25,7 @@ class StringSession(MemorySession):
     * `encode` definition must be ``def encode(value: bytes) -> str:``.
     * `decode` definition must be ``def decode(value: str) -> bytes:``.
     """
-    encode = lambda x: base64.urlsafe_b64encode(x).decode('ascii')
-    decode = base64.urlsafe_b64decode
-
-    def __init__(self, string=None):
+    def __init__(self, string: str = None):
         super().__init__()
         if string:
             if string[0] != CURRENT_VERSION:
@@ -37,18 +34,26 @@ class StringSession(MemorySession):
             string = string[1:]
             ip_len = 4 if len(string) == 352 else 16
             self._dc_id, ip, self._port, key = struct.unpack(
-                _STRUCT_PREFORMAT.format(ip_len), StringSession.decode(string))
+                _STRUCT_PREFORMAT.format(ip_len), self.decode(string))
 
             self._server_address = ipaddress.ip_address(ip).compressed
             if any(key):
                 self._auth_key = AuthKey(key)
 
+    @staticmethod
+    def encode(x: bytes) -> str:
+        return base64.urlsafe_b64encode(x).decode('ascii')
+
+    @staticmethod
+    def decode(x: str) -> bytes:
+        return base64.urlsafe_b64decode(x)
+
     def save(self):
         if not self._auth_key:
             return ''
 
         ip = ipaddress.ip_address(self._server_address).packed
-        return CURRENT_VERSION + StringSession.encode(struct.pack(
+        return CURRENT_VERSION + self.encode(struct.pack(
             _STRUCT_PREFORMAT.format(len(ip)),
             self._dc_id,
             ip,