Replace sys.exit calls with exceptions and return values

Nearly all calls to sys.exit are replaced by khard's custom Cancelled
exception or an explicit return value of type str|int|None.  These are
the values that sys.exit can digest and they are handed outwards to the
exit call with the return value of main().

This should make the code more testable.

Additionally all custom exception are moved to module.

khard/__main__.py

@@ -1,5 +1,7 @@
 #!/usr/bin/env python3
 
+import sys
+
 from .khard import main
 
-main()
+sys.exit(main())

khard/address_book.py

@@ -11,31 +11,13 @@
 import vobject.base
 
 from . import carddav_object
+from .exceptions import AddressBookParseError
 from .query import AnyQuery, Query
 
 
 logger = logging.getLogger(__name__)
 
 
-class AddressBookParseError(Exception):
-    """Indicate an error while parsing data from an address book backend."""
-
-    def __init__(self, filename: str, abook: str, reason: Exception) -> None:
-        """Store the filename that caused the error."""
-        super().__init__()
-        self.filename = filename
-        self.abook = abook
-        self.reason = reason
-
-    def __str__(self) -> str:
-        return "Error when parsing {} in address book {}: {}".format(
-            self.filename, self.abook, self.reason)
-
-
-class AddressBookNameError(Exception):
-    """Indicate an error with an address book name."""
-
-
 class AddressBook(metaclass=abc.ABCMeta):
     """The base class of all address book implementations."""
 

khard/carddav_object.py

@@ -13,7 +13,6 @@
 import logging
 import os
 import re
-import sys
 import time
 from typing import Any, Callable, Literal, Optional, TypeVar, Union, \
     Sequence, overload
@@ -23,6 +22,8 @@
 from ruamel.yaml import YAML
 import vobject
 
+from khard.exceptions import Cancelled
+
 from . import address_book  # pylint: disable=unused-import # for type checking
 from . import helpers
 from .helpers.typing import (Date, ObjectType, PostAddress, StrList,
@@ -1518,11 +1519,9 @@ def write_to_file(self, overwrite: bool = False) -> None:
             with atomic_write(self.filename, overwrite=overwrite) as f:
                 f.write(self.vcard.serialize())
         except vobject.base.ValidateError as err:
-            print("Error: Vcard is not valid.\n{}".format(err))
-            sys.exit(4)
+            raise Cancelled(f"Vcard is not valid.\n{err}", 4)
         except OSError as err:
-            print("Error: Can't write\n{}".format(err))
-            sys.exit(4)
+            raise Cancelled(f"Can't write\n{err}", 4)
 
     def delete_vcard_file(self) -> None:
         try:

khard/cli.py

@@ -5,8 +5,9 @@
 import sys
 
 from .actions import Actions
+from .exceptions import ConfigError
 from .carddav_object import CarddavObject
-from .config import Config, ConfigError
+from .config import Config
 from .query import AndQuery, AnyQuery, parse
 from .version import version as khard_version
 

khard/config.py

@@ -17,8 +17,8 @@
     import validate
 
 from .actions import Actions
-from .address_book import AddressBookCollection, AddressBookNameError, \
-    VdirAddressBook
+from .address_book import AddressBookCollection, VdirAddressBook
+from .exceptions import AddressBookNameError, ConfigError
 from .query import Query
 
 
@@ -29,10 +29,6 @@
 ConfigFile = Union[str, list[str], io.StringIO]
 
 
-class ConfigError(Exception):
-    """Errors during config file parsing"""
-
-
 def validate_command(value: list[str]) -> list[str]:
     """Special validator to check shell commands
 

khard/exceptions.py

@@ -0,0 +1,32 @@
+"""Custom exceptions for khard"""
+
+
+class Cancelled(Exception):
+    """An exception indicating that the user canceled some operation or
+    some backend operation failed"""
+
+    def __init__(self, message: str = "Canceled", code: int = 1) -> None:
+        super().__init__(message)
+        self.code = code
+
+
+class AddressBookParseError(Exception):
+    """Indicate an error while parsing data from an address book backend."""
+
+    def __init__(self, filename: str, abook: str, reason: Exception) -> None:
+        """Store the filename that caused the error."""
+        super().__init__()
+        self.filename = filename
+        self.abook = abook
+        self.reason = reason
+
+    def __str__(self) -> str:
+        return f"Error when parsing {self.filename} in address book {self.abook}: {self.reason}"
+
+
+class AddressBookNameError(Exception):
+    """Indicate an error with an address book name."""
+
+
+class ConfigError(Exception):
+    """Errors during config file parsing"""

khard/helpers/interactive.py

@@ -8,18 +8,13 @@
 from tempfile import NamedTemporaryFile
 from typing import Callable, Generator, Optional, Sequence, TypeVar, Union
 
+from ..exceptions import Cancelled
 from ..carddav_object import CarddavObject
 
 
 T = TypeVar("T")
 
 
-class Canceled(Exception):
-    """An exception indicating that the user canceled some operation."""
-    def __init__(self, message: str = "Canceled") -> None:
-        super().__init__(message)
-
-
 def confirm(message: str, accept_enter_key: bool = True) -> bool:
     """Ask the user for confirmation on the terminal.
 
@@ -74,7 +69,7 @@ def ask(message: str, choices: list[str], default: Optional[str] = None,
         except (EOFError, IndexError, ValueError):
             pass
         except KeyboardInterrupt:
-            raise Canceled
+            raise Cancelled
         if help is not None:
             print(help)
 
@@ -97,7 +92,7 @@ def select(items: Sequence[T], include_none: bool = False) -> Optional[T]:
             answer = input(prompt)
             answer = answer.lower()
             if answer == "q":
-                raise Canceled
+                raise Cancelled
             index = int(answer)
             if include_none and index == 0:
                 return None