feat(misc): parse literals from environment variables (#135)

autotest/test_misc.py

@@ -9,6 +9,7 @@
 import pytest
 
 from modflow_devtools.misc import (
+    get_env,
     get_model_paths,
     get_namefile_paths,
     get_packages,
@@ -280,3 +281,25 @@ def sleep1dec():
     cap = capfd.readouterr()
     print(cap.out)
     assert re.match(r"sleep1dec took \d+\.\d+ ms", cap.out)
+
+
+def test_get_env():
+    assert get_env("NO_VALUE") is None
+
+    with set_env(TEST_VALUE=str(True)):
+        assert get_env("NO_VALUE", True) == True
+        assert get_env("TEST_VALUE") == True
+        assert get_env("TEST_VALUE", default=False) == True
+        assert get_env("TEST_VALUE", default=1) == 1
+
+    with set_env(TEST_VALUE=str(1)):
+        assert get_env("NO_VALUE", 1) == 1
+        assert get_env("TEST_VALUE") == 1
+        assert get_env("TEST_VALUE", default=2) == 1
+        assert get_env("TEST_VALUE", default=2.1) == 2.1
+
+    with set_env(TEST_VALUE=str(1.1)):
+        assert get_env("NO_VALUE", 1.1) == 1.1
+        assert get_env("TEST_VALUE") == 1.1
+        assert get_env("TEST_VALUE", default=2.1) == 1.1
+        assert get_env("TEST_VALUE", default=False) == False

modflow_devtools/misc.py

@@ -2,6 +2,7 @@
 import socket
 import sys
 import traceback
+from ast import literal_eval
 from contextlib import contextmanager
 from functools import wraps
 from importlib import metadata
@@ -31,39 +32,6 @@ def set_dir(path: PathLike):
         print(f"Returned to previous directory: {origin}")
 
 
-@contextmanager
-def set_env(*remove, **update):
-    """
-    Temporarily updates the ``os.environ`` dictionary in-place.
-
-    Referenced from https://stackoverflow.com/a/34333710/6514033.
-
-    The ``os.environ`` dictionary is updated in-place so that the modification
-    is sure to work in all situations.
-
-    :param remove: Environment variables to remove.
-    :param update: Dictionary of environment variables and values to add/update.
-    """
-    env = environ
-    update = update or {}
-    remove = remove or []
-
-    # List of environment variables being updated or removed.
-    stomped = (set(update.keys()) | set(remove)) & set(env.keys())
-    # Environment variables and values to restore on exit.
-    update_after = {k: env[k] for k in stomped}
-    # Environment variables and values to remove on exit.
-    remove_after = frozenset(k for k in update if k not in env)
-
-    try:
-        env.update(update)
-        [env.pop(k, None) for k in remove]
-        yield
-    finally:
-        env.update(update_after)
-        [env.pop(k) for k in remove_after]
-
-
 class add_sys_path:
     """
     Context manager to add temporarily to the system path.
@@ -486,3 +454,68 @@ def call():
         return res
 
     return _timed
+
+
+def get_env(name: str, default: object = None) -> Optional[object]:
+    """
+    Try to parse the given environment variable as the type of the given
+    default value, if one is provided, otherwise any type is acceptable.
+    If the types of the parsed value and default value don't match, the
+    default value is returned. The environment variable is parsed as a
+    Python literal with `ast.literal_eval()`.
+
+    Parameters
+    ----------
+    name : str
+        The environment variable name
+    default : object
+        The default value if the environment variable does not exist
+
+    Returns
+    -------
+    The value of the environment variable, parsed as a Python literal,
+    otherwise the default value if the environment variable is not set.
+    """
+    try:
+        v = environ.get(name)
+        if isinstance(default, bool):
+            v = v.lower().title()
+        v = literal_eval(v)
+    except:
+        return default
+    if default is None:
+        return v
+    return v if isinstance(v, type(default)) else default
+
+
+@contextmanager
+def set_env(*remove, **update):
+    """
+    Temporarily updates the ``os.environ`` dictionary in-place.
+
+    Referenced from https://stackoverflow.com/a/34333710/6514033.
+
+    The ``os.environ`` dictionary is updated in-place so that the modification
+    is sure to work in all situations.
+
+    :param remove: Environment variables to remove.
+    :param update: Dictionary of environment variables and values to add/update.
+    """
+    env = environ
+    update = update or {}
+    remove = remove or []
+
+    # List of environment variables being updated or removed.
+    stomped = (set(update.keys()) | set(remove)) & set(env.keys())
+    # Environment variables and values to restore on exit.
+    update_after = {k: env[k] for k in stomped}
+    # Environment variables and values to remove on exit.
+    remove_after = frozenset(k for k in update if k not in env)
+
+    try:
+        env.update(update)
+        [env.pop(k, None) for k in remove]
+        yield
+    finally:
+        env.update(update_after)
+        [env.pop(k) for k in remove_after]