Support optional leading : in factor arg values.

This aids reading configs and command lines.

CHANGES.md

@@ -1,5 +1,10 @@
 # Release Notes
 
+## 0.13.0
+
+Support an optional leading `:` in factor argument values to parallel factor parameter default
+syntax and better visually separate factor values from factor names.
+
 ## 0.12.0
 
 This change adds support for command parametrization via environment variables, Python interpreter

README.md

@@ -112,7 +112,11 @@ as `test-py3.12`, the `-py3.12` factor will be defined. The value of `3.12` coul
 the `{-py}` factor parameter placeholder in the command arguments or env values. The factor name
 prefix will be stripped from the factor argument to produce the substituted value. As a consequence,
 you want to ensure the factor names you use are non-overlapping or else an error will be raised due
-to ambiguity in which factor argument should be applied.
+to ambiguity in which factor argument should be applied. An optional leading `:` can proceed the
+factor argument value, and it will be stripped. So both `test-py:3.12` and `test-py3.12` pass `3.12`
+as the value for the `-py` factor parameter. The colon-prefix helps distinguish factor name from
+factor value, paralleling the default value syntax that can be used at factor parameter declaration
+sites.
 
 ### Tasks
 

dev_cmd/__init__.py

@@ -1,4 +1,4 @@
 # Copyright 2024 John Sirois.
 # Licensed under the Apache License, Version 2.0 (see LICENSE).
 
-__version__ = "0.12.0"
+__version__ = "0.13.0"

dev_cmd/placeholder.py

@@ -62,6 +62,8 @@ def substitution(self, text: str, section: slice, state: State) -> None:
                 )
             if matching_factors:
                 value = matching_factors[0][len(factor_name) :]
+                if value.startswith(":"):
+                    value = value[1:]
                 state.used_factors.append(matching_factors[0])
             else:
                 value = default

tests/test_placeholder.py

@@ -65,11 +65,11 @@ def test_substitute_markers(env) -> None:
 
 
 def test_substitute_factors(env: Environment) -> None:
-    factors = Factor("a1"), Factor("b2")
+    factors = Factor("a1"), Factor("b:2")
     assert ("1", (Factor("a1"),)) == env.substitute("{-a}", *factors)
-    assert ("2", (Factor("b2"),)) == env.substitute("{-b}", *factors)
-    assert ("12", (Factor("a1"), Factor("b2"))) == env.substitute("{-a}{-b}", *factors)
-    assert ("123", (Factor("a1"), Factor("b2"))) == env.substitute("{-a}{-b}{-c:3}", *factors)
+    assert ("2", (Factor("b:2"),)) == env.substitute("{-b}", *factors)
+    assert ("12", (Factor("a1"), Factor("b:2"))) == env.substitute("{-a}{-b}", *factors)
+    assert ("123", (Factor("a1"), Factor("b:2"))) == env.substitute("{-a}{-b}{-c:3}", *factors)
 
     with pytest.raises(ValueError, match=re.escape("The factor parameter '-c' is not set.")):
         env.substitute("{-c}", *factors)