chore: Add py.typed to start exporting types

* chore: Add py.typed to start exporting types

* chore: Add mypy

* chore: Add mypy to pre-commit

* chore: Name variables in `add_currency` call

Resolves a mypy error.

If you look back at pymoneyed in 2019 when this was
added, the signature of the function was
`def add_currency(code, numeric, name, countries):` (source: https://github.com/py-moneyed/py-moneyed/blob/b3ed12f9aa9c9dec83f9f09b9e1daad7949fe577/moneyed/classes.py#L250)

Now the function signature is a little different:
`def add_currency(code: str, numeric: Optional[str], sub_unit: int = 1, name: Optional[str] = None, countries: Optional[List[str]] = None,)`.

* chore: Fix remaining mypy errors

.pre-commit-config.yaml

@@ -49,3 +49,12 @@ repos:
     hooks:
       - id: black
         exclude: ^docs
+
+-   repo: https://github.com/pre-commit/mirrors-mypy
+    rev: v0.981
+    hooks:
+       - id: mypy
+         additional_dependencies:
+           - django-stubs
+           - py-moneyed
+         files: 'djmoney\/.*\.py|tests\/.*\.py'

djmoney/contrib/exchange/backends/base.py

@@ -1,6 +1,7 @@
 import json
 import ssl
 from decimal import Decimal
+from typing import Optional
 from urllib.parse import parse_qsl, urlparse, urlunparse
 from urllib.request import Request, urlopen
 
@@ -19,8 +20,8 @@
 
 
 class BaseExchangeBackend:
-    name = None
-    url = None
+    name: Optional[str] = None
+    url: Optional[str] = None
 
     def get_rates(self, **kwargs):
         """

djmoney/contrib/exchange/migrations/0001_initial.py

@@ -1,4 +1,5 @@
 # Generated by Django 2.0.4 on 2018-04-03 08:42
+from typing import List, Tuple
 
 import django.db.models.deletion
 from django.db import migrations, models
@@ -10,7 +11,7 @@ class Migration(migrations.Migration):
 
     initial = True
 
-    dependencies = []
+    dependencies: List[Tuple[str, str]] = []
 
     operations = [
         migrations.CreateModel(

djmoney/settings.py

@@ -1,5 +1,6 @@
 import operator
 from types import MappingProxyType
+from typing import Optional
 
 from django.conf import settings
 
@@ -8,7 +9,7 @@
 
 # The default currency, you can define this in your project's settings module
 # This has to be a currency object imported from moneyed
-DEFAULT_CURRENCY: Currency = getattr(settings, "DEFAULT_CURRENCY", None)
+DEFAULT_CURRENCY: Optional[Currency] = getattr(settings, "DEFAULT_CURRENCY", None)
 
 
 # The default currency choices, you can define this in your project's

mypy.ini

@@ -0,0 +1,11 @@
+[mypy]
+python_version = 3.7
+ignore_missing_imports = True
+plugins = mypy_django_plugin.main
+exclude = (?x)(
+          docs/.+
+          | .github/.+
+  )
+
+[mypy.plugins.django-stubs]
+django_settings_module = "djmoney.settings"

setup.py

@@ -32,6 +32,8 @@ def run_tests(self):
     "pytest-pythonpath",
     "pytest-cov",
     "mixer",
+    "mypy",
+    "django-stubs",
 ]
 
 extras_requirements = {

tests/settings.py

@@ -39,7 +39,7 @@
     USE_L10N = True
 
 
-moneyed.add_currency("USDT", "000", "Tether", None)
+moneyed.add_currency(code="USDT", numeric="000", name="Tether")
 
 OPEN_EXCHANGE_RATES_APP_ID = "test"
 FIXER_ACCESS_KEY = "test"

tests/test_models.py

@@ -512,7 +512,7 @@ class TestFExpressions:
             (Money(50, "USD") * F("integer"), Money(100, "USD")),
             (F("integer") * Money(50, "USD"), Money(100, "USD")),
             (Money(50, "USD") / F("integer"), Money(25, "USD")),
-            (Money(51, "USD") % F("integer"), Money(1, "USD")),
+            (Money(51, "USD") % F("integer"), Money(1, "USD")),  # type: ignore
             (F("money") / 2, Money(50, "USD")),
             (F("money") % 98, Money(2, "USD")),
             (F("money") / F("integer"), Money(50, "USD")),