Use Error class to represent CB errors

cloud-build.py

@@ -1,8 +1,9 @@
 #!/usr/bin/python3
 
 import argparse
+import sys
 
-from cloud_build import CB
+import cloud_build
 
 PROG = 'cloud-build'
 
@@ -29,12 +30,16 @@ def parse_args():
 
 def main():
     args = parse_args()
-    cloud_build = CB(args)
-    cloud_build.create_images()
-    cloud_build.copy_external_files()
-    cloud_build.sign()
-    cloud_build.sync()
+    cb = cloud_build.CB(args)
+    cb.create_images()
+    cb.copy_external_files()
+    cb.sign()
+    cb.sync()
 
 
 if __name__ == '__main__':
-    main()
+    try:
+        main()
+    except cloud_build.Error as e:
+        print(e, file=sys.stdout)
+        exit(1)

cloud_build/__init__.py

@@ -1 +1,2 @@
 from .cloud_build import CB  # noqa: F401
+from .cloud_build import Error  # noqa: F401

cloud_build/cloud_build.py

@@ -22,6 +22,10 @@ PROG = 'cloud-build'
 PathLike = Union[Path, str]
 
 
+class Error(Exception):
+    pass
+
+
 class CB:
     """class for building cloud images"""
 
@@ -48,13 +52,13 @@ class CB:
         self.created_scripts: List[Path] = []
 
         self.ensure_dirs()
-        self.ensure_run_once()
         logging.basicConfig(
             filename=f'{data_dir}/{PROG}.log',
             format='%(levelname)s:%(asctime)s - %(message)s',
         )
         self.log = logging.getLogger(PROG)
         self.log.setLevel(self.log_level)
+        self.ensure_run_once()
         self.info(f'Start {PROG}')
         self.initialized = True
 
@@ -91,8 +95,7 @@ class CB:
         try:
             fcntl.flock(self.lock_file.fileno(), fcntl.LOCK_EX | fcntl.LOCK_NB)
         except OSError:  # already locked
-            print(f'{PROG} already running', file=sys.stderr)
-            exit(3)
+            self.error(f'{PROG} already running')
 
     @contextlib.contextmanager
     def pushd(self, new_dir):
@@ -154,7 +157,7 @@ class CB:
 
     def error(self, msg: str) -> None:
         self.log.error(msg)
-        raise Exception(msg)
+        raise Error(msg)
 
     def remote(self, branch: str) -> str:
         return self._remote.format(branch=branch)