Add `allowempty` to StringSpec

configspec/specification.py

@@ -83,17 +83,21 @@ class FloatSpec(_ValueSpecification):
 
 @preservable
 class StringSpec(_ValueSpecification):
-    def __init__(self, regex=None, helptext=""):
+    def __init__(self, regex=None, allowempty=False, helptext=""):
         """
         Specify a string to be provided. If `regex` is not None, validation requires that the
-        config value directly matches the supplied regex string (calls `re.fullmatch`)
+        config value directly matches the supplied regex string (calls `re.fullmatch`). 
+        If `allowempty` is False, validation requires that the string not be an empty or blank.
         """
         super().__init__(helptext)
         self.regex = regex
+        self.allowempty = allowempty
 
     def validate(self, value):
         if not isinstance(value, str):
             raise InvalidConfigError(F"Config value must be a string and is {value}")
+        if not self.allowempty and (value == ""):
+            raise InvalidConfigError("Config value cannot be a blank string")
         if self.regex and (re.fullmatch(self.regex, value) is None):
             raise InvalidConfigError(F"Config string '{value}' must match regex"
                                      F" pattern '{self.regex}'")

tests/test_configspec.py

@@ -15,6 +15,7 @@ def example_spec():
     confspec.add_spec("float_a", FloatSpec(-4, 4, helptext="Float A"))
     confspec.add_spec("floatlist_a", ListSpec(FloatSpec(-4, 4, "Float A")))
     confspec.add_spec("string_a", StringSpec(helptext="String A"))
+    confspec.add_spec("string_a_blank", StringSpec(allowempty=True, helptext="String A Blank"))
     confspec.add_spec("stringlist_a", ListSpec(StringSpec(), helptext="String List A"))
 
     confdictspec = confspec.add_spec("dict_a", DictSpec(helptext="Dict A"))
@@ -42,6 +43,7 @@ def example_values():
             'float_a': 1.5,
             'floatlist_a': [1.2, 2.1, 3.7, 2.8],
             'string_a': 'sometext',
+            'string_a_blank': '',
             'stringlist_a': ['somemoretext', 'yetmoretext'],
             'dict_a': {
                 'bool_b': False,
@@ -100,6 +102,8 @@ def test_invalid_string():
         spec.validate(1)
     with pytest.raises(InvalidConfigError, match="value must be a string"):
         spec.validate(None)
+    with pytest.raises(InvalidConfigError, match="value cannot be a blank string"):
+        spec.validate("")
 
 
 def test_dict_optional():