importers.csvbase: Allow to specifying a default value

Add to all implemented column types the possibility to specify a
default value to return when the parsed field is empty. When a default
is not specified, the empty field is passed to the parser to generate
a value.

beangulp/importers/csvbase.py

@@ -99,10 +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):
@@ -119,10 +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):
@@ -142,11 +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

@@ -63,6 +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):
 
@@ -78,6 +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):
 
@@ -109,6 +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):