Add return type dataclassreader (#57)

* Update dataclass_reader.py

Make DataclassReader a Generic class whose type is defined by the type of dataclass supplied to the init function

* Fix formatting

* Make a generic class

---------

Co-authored-by: Daniel Furtado <jazzmachine77@gmail.com>

Author: danjjackson

dataclass_csv/dataclass_reader.py

@@ -2,7 +2,7 @@
 import csv
 
 from datetime import date, datetime
-from typing import Union, Type, Optional, Sequence, Dict, Any
+from typing import Union, Type, Optional, Sequence, Dict, Any, List, Generic, TypeVar
 
 import typing
 
@@ -11,6 +11,8 @@
 
 from collections import Counter
 
+T = TypeVar("T")
+
 def strtobool(value: str) -> bool:
     trueValues = ["true", "yes", "t", "y", "on", "1"]
 
@@ -54,11 +56,11 @@ def get_args(t):
     return tuple()
 
 
-class DataclassReader:
+class DataclassReader(Generic[T]):
     def __init__(
         self,
         f: Any,
-        cls: Type[object],
+        cls: Type[T],
         fieldnames: Optional[Sequence[str]] = None,
         restkey: Optional[str] = None,
         restval: Optional[Any] = None,
@@ -192,7 +194,7 @@ def _parse_date_value(self, field, date_value, field_type):
         else:
             return datetime_obj
 
-    def _process_row(self, row):
+    def _process_row(self, row) -> T:
         values = dict()
 
         for field in dataclasses.fields(self._cls):
@@ -251,7 +253,7 @@ def _process_row(self, row):
                 values[field.name] = transformed_value
         return self._cls(**values)
 
-    def __next__(self):
+    def __next__(self) -> T:
         row = next(self._reader)
         return self._process_row(row)
 

dataclass_csv/dataclass_reader.pyi

@@ -1,18 +1,21 @@
 from .field_mapper import FieldMapper as FieldMapper
-from typing import Any, Optional, Sequence, Type
+from typing import Any, Optional, Sequence, Type, Generic, TypeVar
 
-class DataclassReader:
+T = TypeVar("T")
+
+
+class DataclassReader(Generic[T]):
     def __init__(
         self,
         f: Any,
-        cls: Type[object],
+        cls: Type[T],
         fieldnames: Optional[Sequence[str]] = ...,
         restkey: Optional[str] = ...,
         restval: Optional[Any] = ...,
         dialect: str = ...,
         *args: Any,
         **kwds: Any
     ) -> None: ...
-    def __next__(self) -> None: ...
+    def __next__(self) -> T: ...
     def __iter__(self) -> Any: ...
     def map(self, csv_fieldname: str) -> FieldMapper: ...