importers.csvbase: Allow to specifying a default value

beangulp/importers/csvbase.py

@@ -13,6 +13,9 @@
 
 EMPTY = frozenset()
 
+NA = object()
+"""Marker to indicate that a value was not specified."""
+
 
 def _resolve(spec, names):
     """Resolve column specification into column index.
@@ -40,10 +43,12 @@ class Column:
 
     Args:
       name: Column name or index.
-      default: Value to return if the field is empty.
-    """
+      default: Value to return if the field is empty. When a default
+        value is not provided, emty fields are passed to the parser
+        to generate a value.
 
-    def __init__(self, *names, default=None):
+    """
+    def __init__(self, *names, default=NA):
         self.names = names
         self.default = default
 
@@ -70,7 +75,7 @@ def getter(self, names):
         idxs = [_resolve(x, names) for x in self.names]
         def func(obj):
             value = tuple(obj[i] for i in idxs)
-            if not all(value) and self.default:
+            if self.default is not NA and not any(value):
                 return self.default
             return self.parse(*value)
         return func
@@ -94,10 +99,11 @@ class Columns(Column):
     Args:
       name: Column names or indexes.
       sep: Separator to use to join columns.
+      default: Value to return all the fields are empty, if specified.
 
     """
-    def __init__(self, *names, sep=' '):
-        super().__init__(*names)
+    def __init__(self, *names, sep=' ', default=NA):
+        super().__init__(*names, default=default)
         self.sep = sep
 
     def parse(self, *values):
@@ -114,10 +120,11 @@ class Date(Column):
     Args:
       name: Column name or index.
       frmt: Date format specification.
+      default: Value to return if the field is empty, if specified.
 
     """
-    def __init__(self, name, frmt='%Y-%m-%d'):
-        super().__init__(name)
+    def __init__(self, name, frmt='%Y-%m-%d', default=NA):
+        super().__init__(name, default=default)
         self.frmt = frmt
 
     def parse(self, value):
@@ -137,11 +144,11 @@ class Amount(Column):
       subs: Dictionary mapping regular expression patterns to
         replacement strings. Substitutions are performed with
         re.sub() in the order they are specified.
+      default: Value to return if the field is empty, if specified.
 
     """
-
-    def __init__(self, name, subs=None):
-        super().__init__(name)
+    def __init__(self, name, subs=None, default=NA):
+        super().__init__(name, default=default)
         self.subs = subs if subs is not None else {}
 
     def parse(self, value):

beangulp/importers/csvbase_test.py

@@ -36,12 +36,18 @@ def test_strip(self):
         value = func((' value ', ))
         self.assertEqual(value, 'value')
 
-    def test_default(self):
+    def test_default_value(self):
         column = Column(0, default=42)
         func = column.getter(None)
         value = func(('', ))
         self.assertEqual(value, 42)
 
+    def test_default_value_none(self):
+        column = Column(0, default=None)
+        func = column.getter(None)
+        value = func(('', ))
+        self.assertIsNone(value)
+
 
 class TestDateColumn(unittest.TestCase):
 
@@ -57,6 +63,18 @@ def test_custom_format(self):
         value = func(('16.05.2021', ))
         self.assertEqual(value, datetime.date(2021, 5, 16))
 
+    def test_default_value(self):
+        column = Date(0, default=datetime.date.today())
+        func = column.getter(None)
+        value = func(('', ))
+        self.assertEqual(value, datetime.date.today())
+
+    def test_default_value_none(self):
+        column = Date(0, default=None)
+        func = column.getter(None)
+        value = func(('', ))
+        self.assertIsNone(value)
+
 
 class TestColumnsColumn(unittest.TestCase):
 
@@ -72,6 +90,24 @@ def test_custom_sep(self):
         value = func(('0', '1', '2', '3', ))
         self.assertEqual(value, '0: 1')
 
+    def test_default_value(self):
+        column = Columns(0, 1, default='something')
+        func = column.getter(None)
+        value = func(('', '', ))
+        self.assertEqual(value, 'something')
+
+    def test_default_value_none(self):
+        column = Columns(0, 1, default=None)
+        func = column.getter(None)
+        value = func(('', '', ))
+        self.assertIsNone(value)
+
+    def test_some_empty(self):
+        column = Columns(0, 1, default=None)
+        func = column.getter(None)
+        value = func(('this', '', ))
+        self.assertEqual(value, 'this')
+
 
 class TestAmountColumn(unittest.TestCase):
 
@@ -103,6 +139,18 @@ def test_parse_subs_currency(self):
         self.assertIsInstance(value, decimal.Decimal)
         self.assertEqual(value, decimal.Decimal('1000.00'))
 
+    def test_default_value(self):
+        column = Amount(0, default=decimal.Decimal(42))
+        func = column.getter(None)
+        value = func(('', ))
+        self.assertEqual(value, decimal.Decimal(42))
+
+    def test_default_value_none(self):
+        column = Amount(0, default=None)
+        func = column.getter(None)
+        value = func(('', ))
+        self.assertIsNone(value)
+
 
 class TestCSVMeta(unittest.TestCase):