Add TemporaryEnvironment context manager

This class sets and restores environment variables within the context.
I'd like to use this in pyiron_base, but thought it'd be nice here as
well.

pyiron_snippets/tempenv.py

@@ -0,0 +1,40 @@
+import os
+import contextlib
+
+@contextlib.contextmanager
+def TemporaryEnvironment(**kwargs):
+    """
+    Context manager for temporarily setting environment variables.
+
+    Takes any number of keyword arguments where the key is the environment 
+    variable to set and the value is the value to set it to. For the duration
+    of the context, the environment variables are set as per the provided arguments.
+    The original environment setting is restored once the context is exited, 
+    even if an exception is raised within the context.
+
+    Non-string values are coerced with `str()`.
+
+    Can also be used as a function decorator.
+
+    Examples:
+
+    >>> with TemporaryEnvironment(PATH='/tmp', HOME='/', USER='foobar'):
+    ...     print(os.getenv('PATH'))  # Outputs: /tmp
+    ...     print(os.getenv('HOME'))  # Outputs: /
+    ...     print(os.getenv('USER'))  # Outputs: foobar
+    """
+    old_vars = {}
+    for k, v in kwargs.items():
+        try:
+            old_vars[k] = os.environ[k]
+        except KeyError:
+            pass
+        os.environ[k] = str(v)
+    try:
+        yield
+    finally:
+        for k, v in kwargs.items():
+            if k in old_vars:
+                os.environ[k] = v
+            else:
+                del os.environ[k]

tests/unit/test_tempenv.py

@@ -0,0 +1,69 @@
+import os
+import unittest
+from pyiron_base.utils.tempenv import TemporaryEnvironment
+
+class TestTemporaryEnvironment(unittest.TestCase):
+    """
+    Class to test TemporaryEnvironment context manager.
+    """
+
+    def setUp(self):
+        """Ensures the original environment is kept intact before each test."""
+        self.old_environ = dict(os.environ)
+
+    def tearDown(self):
+        """Ensures the original environment is restored after each test."""
+        os.environ.clear()
+        os.environ.update(self.old_environ)
+
+    def test_value_int(self):
+        """Should correctly convert and store integer values as strings."""
+        with TemporaryEnvironment(FOO=12):
+            self.assertEqual(os.environ.get('FOO'), '12', "Failed to convert integer to string")
+
+    def test_value_bool(self):
+        """Should correctly convert and store boolean values as strings."""
+        with TemporaryEnvironment(FOO=True):
+            self.assertEqual(os.environ.get('FOO'), 'True', "Failed to convert boolean to string")
+
+    def test_environment_set(self):
+        """Should correctly set environment variables inside its scope."""
+        with TemporaryEnvironment(FOO='1', BAR='2'):
+            self.assertEqual(os.environ.get('FOO'), '1', "Failed to set FOO")
+            self.assertEqual(os.environ.get('BAR'), '2', "Failed to set BAR")
+
+    def test_environment_restored(self):
+        """Should restore original environment variables state after leaving its scope."""
+        os.environ['FOO'] = '0'
+        with TemporaryEnvironment(FOO='1'):
+            self.assertEqual(os.environ.get('FOO'), '1')
+        self.assertEqual(os.environ.get('FOO'), '0', "Failed to restore original FOO value")
+
+    def test_environment_deleted(self):
+        """Should correctly delete environment variables that didn't exist originally after leaving its scope."""
+        with TemporaryEnvironment(FOO='1'):
+            self.assertEqual(os.environ.get('FOO'), '1')
+        self.assertIsNone(os.environ.get('FOO'), "Failed to delete FOO")
+
+    def test_raise_exception(self):
+        """Should restore original environment after handling an exception within its scope."""
+        os.environ['FOO'] = '0'
+        try:
+            with TemporaryEnvironment(FOO='1'):
+                self.assertEqual(os.environ.get('FOO'), '1')
+                raise Exception('Some Error')
+        except:
+            self.assertEqual(os.environ.get('FOO'), '0', "Failed to restore environment after exception")
+
+    def test_as_decorator(self):
+        """Should correctly set and restore environment variables when used as a decorator."""
+        @TemporaryEnvironment(FOO='1')
+        def test_func():
+            return os.environ.get('FOO')
+
+        self.assertEqual(test_func(), '1', "Failed to set environment as decorator")
+        self.assertEqual(os.environ.get('FOO', None), None, "Failed to restore environment as decorator")
+
+
+if __name__ == "__main__":
+    unittest.main()