importers: Refactor out a base CSV importer class.

I'm going to build the Stripe importer on top of this.

import2ledger/importers/_csv.py

@@ -0,0 +1,42 @@
+import csv
+
+class CSVImporterBase:
+    """Common base class for importing CSV files.
+
+    Subclasses must define the following:
+    * TEMPLATE_KEY: A string, as usual
+    * NEEDED_FIELDS: A set of columns that must exist in the CSV file for
+      this class to import it.
+    * _read_row(self, row): A method that returns an entry data dict, or None
+      if there's nothing to import from this row.
+
+    Subclasses may define the following:
+    * ENTRY_SEED: A dict with the initial entry data.
+    * COPIED_FIELDS: A dict that maps column names to data keys.  These fields
+      will be copied directly to the entry data dict before _read_row is called.
+      Fields named here must exist in the CSV for it to be imported.
+    """
+    ENTRY_SEED = {}
+    COPIED_FIELDS = {}
+
+    @classmethod
+    def can_import(cls, input_file):
+        in_csv = csv.reader(input_file)
+        fields = next(iter(in_csv), [])
+        return cls.NEEDED_FIELDS.union(cls.COPIED_FIELDS).issubset(fields)
+
+    def __init__(self, input_file):
+        self.in_csv = csv.DictReader(input_file)
+        self.entry_seed = self.ENTRY_SEED.copy()
+
+    def __iter__(self):
+        for row in self.in_csv:
+            row_data = self._read_row(row)
+            if row_data is not None:
+                retval = self.entry_seed.copy()
+                retval.update(
+                    (entry_key, row[row_key])
+                    for row_key, entry_key in self.COPIED_FIELDS.items()
+                )
+                retval.update(row_data)
+                yield retval

import2ledger/importers/patreon.py

@@ -1,37 +1,21 @@
-import csv
-import datetime
 import pathlib
 import re
 
+from . import _csv
 from .. import util
 
-class ImporterBase:
-    @classmethod
-    def can_import(cls, input_file):
-        in_csv = csv.reader(input_file)
-        fields = next(iter(in_csv), [])
-        return cls.NEEDED_FIELDS.issubset(fields)
-
-    def __init__(self, input_file):
-        self.in_csv = csv.DictReader(input_file)
-        self.start_data = {'currency': 'USD'}
-
-    def __iter__(self):
-        for row in self.in_csv:
-            row_data = self._read_row(row)
-            if row_data is not None:
-                retval = self.start_data.copy()
-                retval.update(row_data)
-                yield retval
-
-
-class IncomeImporter(ImporterBase):
+class IncomeImporter(_csv.CSVImporterBase):
     NEEDED_FIELDS = frozenset([
         'FirstName',
         'LastName',
-        'Pledge',
         'Status',
     ])
+    COPIED_FIELDS = {
+        'Pledge': 'amount',
+    }
+    ENTRY_SEED = {
+        'currency': 'USD',
+    }
     TEMPLATE_KEY = 'template patreon income'
 
     def __init__(self, input_file):
@@ -39,28 +23,28 @@ class IncomeImporter(ImporterBase):
         match = re.search(r'(?:\b|_)(\d{4}-\d{2}-\d{2})(?:\b|_)',
                           pathlib.Path(input_file.name).name)
         if match:
-            self.start_data['date'] = util.strpdate(match.group(1), '%Y-%m-%d')
+            self.entry_seed['date'] = util.strpdate(match.group(1), '%Y-%m-%d')
 
     def _read_row(self, row):
         if row['Status'] != 'Processed':
             return None
         else:
             return {
-                'amount': row['Pledge'],
                 'payee': '{0[FirstName]} {0[LastName]}'.format(row),
             }
 
 
-class FeeImporterBase(ImporterBase):
+class FeeImporterBase(_csv.CSVImporterBase):
+    ENTRY_SEED = {
+        'currency': 'USD',
+        'payee': "Patreon",
+    }
+
     def _read_row(self, row):
-        retval = {
-            key.lower().replace(' ', '_'): row[key]
-            for key in self.NEEDED_FIELDS.difference([self.AMOUNT_FIELD, 'Month'])
+        return {
+            'amount': row[self.AMOUNT_FIELD].lstrip('$'),
+            'date': util.strpdate(row['Month'], '%Y-%m'),
         }
-        retval['amount'] = row[self.AMOUNT_FIELD].lstrip('$')
-        retval['date'] = util.strpdate(row['Month'], '%Y-%m')
-        retval['payee'] = "Patreon"
-        return retval
 
 
 class PatreonFeeImporter(FeeImporterBase):
@@ -77,5 +61,9 @@ class CardFeeImporter(FeeImporterBase):
 
 class VATImporter(FeeImporterBase):
     AMOUNT_FIELD = 'Vat Charged'
-    NEEDED_FIELDS = frozenset(['Country Code', 'Country Name', 'Month', AMOUNT_FIELD])
+    NEEDED_FIELDS = frozenset(['Month', AMOUNT_FIELD])
+    COPIED_FIELDS = {
+        'Country Code': 'country_code',
+        'Country Name': 'country_name',
+    }
     TEMPLATE_KEY = 'template patreon vat'