Change Choice.shortcut_key to property with setter (#349)

* Make `Choice.shortcut_key` property with setter

Ensures that `Choice.auto_shortcut` is set to `False`
whenever `Choice.shortcut_key` is set to a `str` value
and vice versa. Add tests for fix.

Fixes #340

Signed-off-by: Ross Williams <[email protected]>

* Make Choice.auto_shortcut a property attribute

`auto_shortcut` and `shortcut_key` interact in ways that requires logic
when setting either, to ensure that they do not conflict.

Signed-off-by: Ross Williams <[email protected]>

* Update questionary/prompts/common.py

---------

Signed-off-by: Ross Williams <[email protected]>

questionary/prompts/common.py

@@ -69,8 +69,7 @@ class Choice:
     checked: Optional[bool]
     """Whether the choice is initially selected"""
 
-    shortcut_key: Optional[str]
-    """A shortcut key for the choice"""
+    __shortcut_key: Optional[Union[str, bool]]
 
     description: Optional[str]
     """Choice description"""
@@ -86,6 +85,8 @@ def __init__(
     ) -> None:
         self.disabled = disabled
         self.title = title
+        self.shortcut_key = shortcut_key
+        # self.auto_shortcut is set by the self.shortcut_key setter
         self.checked = checked if checked is not None else False
         self.description = description
 
@@ -96,17 +97,6 @@ def __init__(
         else:
             self.value = title
 
-        if shortcut_key is not None:
-            if isinstance(shortcut_key, bool):
-                self.auto_shortcut = shortcut_key
-                self.shortcut_key = None
-            else:
-                self.shortcut_key = str(shortcut_key)
-                self.auto_shortcut = False
-        else:
-            self.shortcut_key = None
-            self.auto_shortcut = True
-
     @staticmethod
     def build(c: Union[str, "Choice", Dict[str, Any]]) -> "Choice":
         """Create a choice object from different representations.
@@ -134,12 +124,54 @@ def build(c: Union[str, "Choice", Dict[str, Any]]) -> "Choice":
                 c.get("description", None),
             )
 
+    @property
+    def shortcut_key(self) -> Optional[Union[str, bool]]:
+        """A shortcut key for the choice"""
+        return self.__shortcut_key
+
+    @shortcut_key.setter
+    def shortcut_key(self, key: Optional[Union[str, bool]]):
+        if key is not None:
+            if isinstance(key, bool):
+                self.__auto_shortcut = key
+                self.__shortcut_key = None
+            else:
+                self.__shortcut_key = str(key)
+                self.__auto_shortcut = False
+        else:
+            self.__shortcut_key = None
+            self.__auto_shortcut = True
+
+    @shortcut_key.deleter
+    def shortcut_key(self):
+        self.__shortcut_key = None
+        self.__auto_shortcut = True
+
     def get_shortcut_title(self):
         if self.shortcut_key is None:
             return "-) "
         else:
             return "{}) ".format(self.shortcut_key)
 
+    @property
+    def auto_shortcut(self) -> bool:
+        """Whether to assign a shortcut key to the choice
+
+        Keys are assigned starting with numbers and proceeding
+        through the ASCII alphabet.
+        """
+        return self.__auto_shortcut
+
+    @auto_shortcut.setter
+    def auto_shortcut(self, should_assign: bool):
+        self.__auto_shortcut = should_assign
+        if self.__auto_shortcut:
+            self.__shortcut_key = None
+
+    @auto_shortcut.deleter
+    def auto_shortcut(self):
+        self.__auto_shortcut = False
+
 
 class Separator(Choice):
     """Used to space/separate choices group."""

tests/prompts/test_select.py

@@ -1,4 +1,6 @@
 # -*- coding: utf-8 -*-
+from copy import copy
+
 import pytest
 
 from questionary import Choice
@@ -199,6 +201,29 @@ def test_allow_shortcut_key_with_True():
     assert result == "bazz"
 
 
+def test_auto_shortcut_key_stable_in_loop():
+    message = "Foo message"
+    choices = [
+        Choice("foo"),
+        Choice("bar"),
+    ]
+    kwargs = {
+        "choices": choices,
+        "use_shortcuts": True,
+    }
+    text = "\r"
+
+    result, cli = feed_cli_with_input("select", message, text, **kwargs)
+    assert result == "foo"
+    result_shortcut_keys = [copy(c.shortcut_key) for c in choices]
+    result2, cli = feed_cli_with_input("select", message, text, **kwargs)
+    assert result2 == "foo"
+    result2_shortcut_keys = [copy(c.shortcut_key) for c in choices]
+    assert (
+        result_shortcut_keys == result2_shortcut_keys
+    ), "Shortcut keys changed across two runs of 'select'"
+
+
 def test_select_initial_choice_with_value():
     message = "Foo message"
     choice = Choice(title="bazz", value="bar")