Add type hinting to external API (dfurtado#37)

This should allow dataclass-csv consumers to rely on type hinting more fully
rather than ignoring the import as Any's.

We also check that our code remains type safe with mypy.

Note that flake8 doesn't work, who knows for how long, so we run mypy first
since that is clean.

Author: SpamapS

Makefile

@@ -50,7 +50,8 @@ clean-test: ## remove test and coverage artifacts
 	rm -fr htmlcov/
 	rm -fr .pytest_cache
 
-lint: ## check style with flake8
+lint: ## check style with mypy and flake8
+	mypy dataclass_csv tests
 	flake8 dataclass-csv tests
 
 test: ## run tests quickly with the default Python

Pipfile

@@ -5,6 +5,7 @@ name = "pypi"
 
 [dev-packages]
 pytest = "*"
+mypy = "*"
 
 [packages]
 

Pipfile.lock

@@ -3,7 +3,7 @@
 
 from datetime import datetime
 from distutils.util import strtobool
-from typing import Union
+from typing import Union, Type, Optional, Sequence, Dict, Any, List
 
 from .field_mapper import FieldMapper
 from .exceptions import CsvValueError
@@ -13,13 +13,13 @@ class DataclassReader:
     def __init__(
         self,
         f,
-        cls,
-        fieldnames=None,
-        restkey=None,
-        restval=None,
-        dialect='excel',
-        *args,
-        **kwds,
+        cls: Type[object],
+        fieldnames: Optional[Sequence[str]]=None,
+        restkey: Optional[str]=None,
+        restval: Optional[Any]=None,
+        dialect: str='excel',
+        *args: List[Any],
+        **kwds: Dict[str, Any],
     ):
 
         if not f:
@@ -30,7 +30,7 @@ def __init__(
 
         self.cls = cls
         self.optional_fields = self._get_optional_fields()
-        self.field_mapping = {}
+        self.field_mapping: Dict[str, Dict[str, Any]] = {}
 
         self.reader = csv.DictReader(
             f, fieldnames, restkey, restval, dialect, *args, **kwds
@@ -206,7 +206,7 @@ def __next__(self):
     def __iter__(self):
         return self
 
-    def map(self, csv_fieldname):
+    def map(self, csv_fieldname: str) -> FieldMapper:
         """Used to map a field in the CSV file to a `dataclass` field
         :param csv_fieldname: The name of the CSV field
         """

dataclass_csv/dataclass_reader.py

@@ -1,4 +1,8 @@
-def dateformat(date_format):
+from typing import Any, Callable, TypeVar, Type
+
+F = TypeVar('F', bound=Callable[..., Any])
+
+def dateformat(date_format: str) -> Callable[[F], F]:
     """The dateformat decorator is used to specify the format
     the `DataclassReader` should use when parsing datetime strings.
 
@@ -25,7 +29,7 @@ def func(cls):
     return func
 
 
-def accept_whitespaces(_cls=None):
+def accept_whitespaces(_cls: Type[Any]=None) -> Callable[[F], F]:
     """The accept_whitespaces decorator tells the `DataclassReader`
     that `str` fields defined in the `dataclass` should accept
     values containing only white spaces.

dataclass_csv/decorators.py

@@ -1,9 +1,11 @@
+from typing import Any, Callable
+
 class FieldMapper:
     """The `FieldMapper` class is used to explicitly map a field
     in the CSV file to a specific `dataclass` field.
     """
 
-    def __init__(self, callback):
+    def __init__(self, callback: Callable[[str], Any]):
         def to(property_name):
             """Specify the dataclass field to receive the value
             :param property_name: The dataclass property that

dataclass_csv/field_mapper.py

@@ -67,7 +67,7 @@ class DataclassWithBooleanValue:
 
 @dataclasses.dataclass
 class DataclassWithBooleanValueNoneDefault:
-    boolValue: bool = None
+    boolValue: Optional[bool] = None
 
 
 @dataclasses.dataclass