enhancements to truth()

Author: Ken Kundert

doc/releases.rst

@@ -9,6 +9,8 @@ Latest development release
     | Version: 1.35
     | Released: 2025-07-30
 
+- Added *is_true* argument and value format specification to :class:`truth`.
+
 
 1.35 (2025-07-30)
 -----------------

inform/inform.py

@@ -1566,17 +1566,55 @@ class truth:
 
     If '/', or '%' are inconvenient, you can change them by passing the
     *slash* and *interpolate* arguments to truth().
+
+    By default *bool*() is used to determine whether the value is true or false.
+    However you can override this behavior by passing a value to *is_true*.  It
+    may be a simple value or it may be a callable that accepts the given value 
+    as its only argument.
+
+    The formatter may contain a third section, which if present is taken to be a
+    format specification that is applied to value before it is interpolated into
+    the output.
+
+    As an example of these features, consider this example:
+
+        >>> contestants = [
+        ...     dict(name="Elinor", index=27, wins="car" ),
+        ...     dict(name="Vernon", index=130, wins="phone"),
+        ...     dict(name="Lee",    index=0),
+        ...     dict(name="Lita", comment='disqualified'),
+        ... ]
+
+        >>> for contestant in contestants:
+        ...     name = contestant.get('name')
+        ...     index = contestant.get('index')
+        ...     index = truth(index, is_true=index is not None)
+        ...     wins = truth(contestant.get('wins'))
+        ...     comment = truth(contestant.get('comment'))
+        ...     print(f"{index:%/  ✗/>3}: {name}{wins: wins a %/ loses}{comment: (%)/}")
+         27: Elinor wins a car
+        130: Vernon wins a phone
+          0: Lee loses
+          ✗: Lita loses (disqualified)
+
     """
 
-    def __init__(self, value, formatter=None, *, interpolate='%', slash='/'):
+    def __init__(self, value, formatter=None, *, is_true=None, interpolate='%', slash='/'):
         self.value = value
+        if is_true is None:
+            self.is_true = bool(value)
+        elif callable(is_true):
+            self.is_true = is_true(value)
+        else:
+            self.is_true = bool(is_true)
         self.interpolate = interpolate
         self.slash = slash
         if formatter:
-            use_if_true, _, use_if_false = formatter.partition(self.slash)
-            self.defaults = use_if_true, use_if_false
+            use_if_true, _, rest = formatter.partition(self.slash)
+            use_if_false, _, preformatter = rest.partition(self.slash)
+            self.defaults = use_if_true, use_if_false, preformatter
         else:
-            self.defaults = 'yes', 'no'
+            self.defaults = 'yes', 'no', ''
 
     def format(self, formatter=None):
         """Expand truth to a string.
@@ -1593,19 +1631,22 @@ def format(self, formatter=None):
         return self.__format__(formatter)
 
     def __format__(self, formatter):
-        value = self.value
         if formatter:
-            use_if_true, _, use_if_false = formatter.partition(self.slash)
+            use_if_true, _, rest = formatter.partition(self.slash)
+            use_if_false, _, preformatter = rest.partition(self.slash)
         else:
-            use_if_true, use_if_false = self.defaults
-        out = use_if_true if bool(value) else use_if_false
-        return out.replace(self.interpolate, str(value))
+            use_if_true, use_if_false, preformatter = self.defaults
+        out = use_if_true if self.is_true else use_if_false
+        value = str(self.value)
+        if preformatter and self.interpolate in out:
+            value = f"{self.value:{preformatter}}"
+        return out.replace(self.interpolate, value)
 
     def __str__(self):
-        return self.defaults[0] if self.value else self.defaults[1]
+        return self.defaults[0] if self.is_true else self.defaults[1]
 
     def __bool__(self):
-        return bool(self.value)
+        return self.is_true
 
     def __repr__(self):
         return f"{self.__class__.__name__}({bool(self.value)})"

pyproject.toml

@@ -49,7 +49,7 @@ build-backend = "flit_core.buildapi"
 addopts = "--tb=short"
 
 [tool.ruff]
-exclude = [".tox", "doc", "Diffs"]
+exclude = [".tox", "doc", ".diffs"]
 
 [tool.ruff.lint]
 select = ["F"]

tests/test_zdoctests.py

@@ -22,8 +22,8 @@ def test_inform():
         return
 
     rv = doctest.testfile('../inform/inform.py', optionflags=doctest.ELLIPSIS)
-    assert rv.attempted in [183, 184]
-        # for some reason 181 test are run on my laptop, and 180 on github
+    assert rv.attempted in [185, 186]
+        # for some reason my laptop runs one more test that github
     assert rv.failed == 0
 
 def test_manual():