fix pylint errors

selfdrive/updated.py

@@ -283,8 +283,8 @@ def main():
   ov_lock_fd = open(LOCK_FILE, 'w')
   try:
     fcntl.flock(ov_lock_fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
-  except IOError:
+  except IOError as e:
-    raise RuntimeError("couldn't get overlay lock; is another updated running?")
+    raise RuntimeError("couldn't get overlay lock; is another updated running?") from e
 
   # Wait for IsOffroad to be set before our first update attempt
   wait_helper = WaitTimeHelper(proc)

tools/lib/auth_config.py

@@ -21,8 +21,8 @@ def get_token():
     with open(os.path.join(CONFIG_DIR, 'auth.json')) as f:
       auth = json.load(f)
       return auth['access_token']
-  except Exception:
+  except Exception as e:
-    raise MissingAuthConfigError('Authenticate with tools/lib/auth.py')
+    raise MissingAuthConfigError('Authenticate with tools/lib/auth.py') from e
 
 
 def set_token(token):

tools/lib/logreader.py

@@ -27,8 +27,8 @@ def index_log(fn):
 
   try:
     dat = subprocess.check_output([index_log, fn, "-"])
-  except subprocess.CalledProcessError:
+  except subprocess.CalledProcessError as e:
-    raise DataUnreadableError("%s capnp is corrupted/truncated" % fn)
+    raise DataUnreadableError("%s capnp is corrupted/truncated" % fn) from e
   return np.frombuffer(dat, dtype=np.uint64)
 
 def event_read_multiple_bytes(dat):