Add enum parser (#185)

* Add enum parser

* Add enum description to readme

* Add ignore_case argument to enum parser

* Changed enum to choice in env.parser_for example in README

* Make type arg in enum parser positional

* Update changelog

Co-authored-by: Steven Loria <sloria1@gmail.com>

CHANGELOG.md

@@ -4,9 +4,11 @@
 
 Features:
 
+- Add `enum` parser ([#185](https://github.com/sloria/environs/pull/185)).
 - Add `delimiter` param to `env.list`
   ([#184](https://github.com/sloria/environs/pull/184)).
-  Thanks [tomgrin10](https://github.com/tomgrin10?) for the PR.
+
+Thanks [tomgrin10](https://github.com/tomgrin10?) for the PRs.
 
 Bug fixes:
 

README.md

@@ -109,6 +109,7 @@ The following are all type-casting methods of `Env`:
 - `env.uuid`
 - `env.log_level`
 - `env.path` (casts to a [`pathlib.Path`](https://docs.python.org/3/library/pathlib.html))
+- `env.enum` (casts to any given enum type specified in `type` keyword argument, accepts optional `ignore_case` keyword argument)
 
 ## Reading `.env` files
 
@@ -286,14 +287,14 @@ domain = env.furl("DOMAIN")  # => furl('https://myapp.com')
 
 
 # Custom parsers can take extra keyword arguments
-@env.parser_for("enum")
-def enum_parser(value, choices):
+@env.parser_for("choice")
+def choice_parser(value, choices):
     if value not in choices:
         raise environs.EnvError("Invalid!")
     return value
 
 
-color = env.enum("COLOR", choices=["black"])  # => raises EnvError
+color = env.choice("COLOR", choices=["black"])  # => raises EnvError
 ```
 
 ## Usage with Flask

environs/__init__.py

@@ -9,6 +9,7 @@
 import typing
 import types
 from collections.abc import Mapping
+from enum import Enum
 from urllib.parse import urlparse, ParseResult
 from pathlib import Path
 
@@ -177,6 +178,25 @@ def _preprocess_json(value: str, **kwargs):
     return pyjson.loads(value)
 
 
+_EnumT = typing.TypeVar("_EnumT", bound=Enum)
+
+
+def _enum_parser(value, type: typing.Type[_EnumT], ignore_case: bool = False) -> _EnumT:
+    invalid_exc = ma.ValidationError(f"Not a valid '{type.__name__}' enum.")
+
+    if not ignore_case:
+        try:
+            return type[value]
+        except KeyError as error:
+            raise invalid_exc from error
+
+    for enum_value in type:
+        if enum_value.name.lower() == value.lower():
+            return enum_value
+
+    raise invalid_exc
+
+
 def _dj_db_url_parser(value: str, **kwargs) -> dict:
     try:
         import dj_database_url
@@ -276,6 +296,7 @@ class Env:
     timedelta = _field2method(ma.fields.TimeDelta, "timedelta")
     uuid = _field2method(ma.fields.UUID, "uuid")
     url = _field2method(URLField, "url")
+    enum = _func2method(_enum_parser, "enum")
     dj_db_url = _func2method(_dj_db_url_parser, "dj_db_url")
     dj_email_url = _func2method(_dj_email_url_parser, "dj_email_url")
     dj_cache_url = _func2method(_dj_cache_url_parser, "dj_cache_url")

tests/test_environs.py

@@ -5,6 +5,7 @@
 import urllib.parse
 import pathlib
 from decimal import Decimal
+from enum import Enum
 
 import dj_database_url
 import dj_email_url
@@ -35,6 +36,12 @@ class FauxTestException(Exception):
     pass
 
 
+class DayEnum(Enum):
+    SUNDAY = 1
+    MONDAY = 2
+    TUESDAY = 3
+
+
 class TestCasting:
     def test_call(self, set_env, env):
         set_env({"STR": "foo", "INT": "42"})
@@ -204,6 +211,24 @@ def test_invalid_url(self, url, set_env, env):
             env.url("URL")
         assert 'Environment variable "URL" invalid' in excinfo.value.args[0]
 
+    def test_enum_cast(self, set_env, env):
+        set_env({"DAY": "SUNDAY"})
+        assert env.enum("DAY", type=DayEnum) == DayEnum.SUNDAY
+
+    def test_enum_cast_ignore_case(self, set_env, env):
+        set_env({"DAY": "suNDay"})
+        assert env.enum("DAY", type=DayEnum, ignore_case=True) == DayEnum.SUNDAY
+
+    def test_invalid_enum(self, set_env, env):
+        set_env({"DAY": "suNDay"})
+        with pytest.raises(environs.EnvError):
+            assert env.enum("DAY", type=DayEnum)
+
+    def test_invalid_enum_ignore_case(self, set_env, env):
+        set_env({"DAY": "SonDAY"})
+        with pytest.raises(environs.EnvError):
+            assert env.enum("DAY", type=DayEnum, ignore_case=True)
+
 
 class TestEnvFileReading:
     def test_read_env(self, env):
@@ -320,17 +345,17 @@ def https_url(value):
     def test_parser_function_can_take_extra_arguments(self, set_env, env):
         set_env({"ENV": "dev"})
 
-        @env.parser_for("enum")
-        def enum_parser(value, choices):
+        @env.parser_for("choice")
+        def choice_parser(value, choices):
             if value not in choices:
                 raise environs.EnvError("Invalid!")
             return value
 
-        assert env.enum("ENV", choices=["dev", "prod"]) == "dev"
+        assert env.choice("ENV", choices=["dev", "prod"]) == "dev"
 
         set_env({"ENV": "invalid"})
         with pytest.raises(environs.EnvError):
-            env.enum("ENV", choices=["dev", "prod"])
+            env.choice("ENV", choices=["dev", "prod"])
 
     def test_add_parser_from_field(self, set_env, env):
         class HTTPSURL(fields.Field):