Contingent validation & optional columns

pandas_schema/column.py

@@ -5,7 +5,9 @@
 from .validation_warning import ValidationWarning
 
 class Column:
-    def __init__(self, name: str, validations: typing.Iterable['validation._BaseValidation'] = [], allow_empty=False):
+    def __init__(self, name: str, validations: typing.Iterable['validation._BaseValidation'] = [],
+                 allow_empty=False,
+                 optional=False):
         """
         Creates a new Column object
 
@@ -16,6 +18,7 @@ def __init__(self, name: str, validations: typing.Iterable['validation._BaseVali
         self.name = name
         self.validations = list(validations)
         self.allow_empty = allow_empty
+        self.optional = optional
 
     def validate(self, series: pd.Series) -> typing.List[ValidationWarning]:
         """

pandas_schema/schema.py

@@ -73,7 +73,7 @@ def validate(self, df: pd.DataFrame, columns: typing.List[str] = None) -> typing
             for column in columns_to_pair:
 
                 # Throw an error if the schema column isn't in the data frame
-                if column.name not in df:
+                if column.name not in df and not column.optional:
                     errors.append(ValidationWarning(
                         'The column {} exists in the schema but not in the data frame'.format(column.name)))
                     return errors

pandas_schema/validation.py

@@ -90,7 +90,8 @@ def get_errors(self, series: pd.Series, column: 'column.Column'):
                 validated = ~series.isnull() & simple_validation
             else:
                 validated = (series.str.len() > 0) & simple_validation
-
+        elif column.optional and (bool(series.isnull().all()) or list(series.unique()) == ['']):
+            validated = []
         else:
             validated = simple_validation
 

test/test_validation.py

@@ -660,6 +660,18 @@ def test_in_range_allow_empty_false_with_error(self):
         errors = validator.get_errors(pd.Series(self.vals), Column('', allow_empty=False))
         self.assertEqual(len(errors), len(self.vals))
 
+    def test_in_range_optional_missing(self):
+        validator = InRangeValidation(min=0)
+        errors = validator.get_errors(pd.Series(), Column('', optional=True))
+
+        self.assertEqual(len(errors), 0)
+
+    def test_in_range_optional_with_error(self):
+        validator = InRangeValidation(min=4)
+        errors = validator.get_errors(pd.Series(self.vals), Column('', optional=False))
+
+        self.assertEqual(len(errors), len(self.vals))
+
 
 class PandasDtypeTests(ValidationTestBase):
     """