config: Add open_output_file method.

Make this functionality accessible to hooks.

import2ledger/__main__.py

@@ -43,12 +43,7 @@ class FileImporter:
             'source_path': in_path.as_posix(),
             'source_stem': in_path.stem,
         }
-        with contextlib.ExitStack() as exit_stack:
-            output_path = self.config.get_output_path()
-            if output_path is None:
-                out_file = self.stdout
-            else:
-                out_file = exit_stack.enter_context(output_path.open('a'))
+        with self.config.open_output_file() as out_file:
             for importer, template in importers:
                 in_file.seek(0)
                 for entry_data in importer(in_file):
@@ -106,7 +101,7 @@ def decimal_context(base=decimal.BasicContext):
 
 def main(arglist=None, stdout=sys.stdout, stderr=sys.stderr):
     try:
-        my_config = config.Configuration(arglist)
+        my_config = config.Configuration(arglist, stdout, stderr)
     except errors.UserInputError as error:
         my_config.error("{}: {!r}".format(error.strerror, error.user_input))
         return 3

import2ledger/config.py

@@ -28,7 +28,10 @@ class Configuration:
         'unsigned_currency_format': '#,##0.### ¤¤',
     }
 
-    def __init__(self, arglist):
+    def __init__(self, arglist, stdout, stderr):
+        self.stdout = stdout
+        self.stderr = stderr
+
         argparser = self._build_argparser()
         self.error = argparser.error
         self.args = argparser.parse_args(arglist)
@@ -186,6 +189,14 @@ class Configuration:
                             for secname in self.conffile}
         self.date_ranges[default_secname] = self._parse_date_range(default_secname)
 
+    @contextlib.contextmanager
+    def _open_path(self, path, fallback_file, *args, **kwargs):
+        if path is None:
+            yield fallback_file
+        else:
+            with path.open(*args, **kwargs) as open_file:
+                yield open_file
+
     @contextlib.contextmanager
     def from_section(self, section_name):
         prev_section = self.args.use_config
@@ -226,6 +237,10 @@ class Configuration:
         section_config = self._get_section(section_name)
         return self._s_to_path(section_config['output_path'])
 
+    def open_output_file(self, section_name=None):
+        path = self.get_output_path(section_name)
+        return self._open_path(path, self.stdout, 'a')
+
     def get_template(self, config_key, section_name=None, factory=template.Template):
         section_config = self._get_section(section_name)
         try:

tests/test_config.py

@@ -14,12 +14,12 @@ from import2ledger import config, errors
 
 from . import DATA_DIR
 
-def config_from_file(path, arglist=[]):
+def config_from_file(path, arglist=[], stdout=None, stderr=None):
     path = pathlib.Path(path)
     if not path.is_absolute():
         path = DATA_DIR / path
     arglist = ['-C', path.as_posix(), *arglist, os.devnull]
-    return config.Configuration(arglist)
+    return config.Configuration(arglist, stdout, stderr)
 
 def test_defaults():
     config = config_from_file('test_config.ini', ['--sign', 'GBP', '-O', 'out_arg'])