event on_envvar

news/event-envvar.rst

@@ -0,0 +1,13 @@
+**Added:**
+
+* new event ``on_envvar`` that fires after an enviroment variable has been changed.
+
+**Changed:** None
+
+**Deprecated:** None
+
+**Removed:** None
+
+**Fixed:** None
+
+**Security:** None

tests/test_environ.py

@@ -140,3 +140,19 @@ def test_locate_binary_on_windows(xonsh_builtins):
         assert locate_binary('file2') == os.path.join(tmpdir, 'FILE2.BAT')
         assert locate_binary('file2.bat') == os.path.join(tmpdir, 'FILE2.BAT')
         assert locate_binary('file3') is None
+
+
+def test_event_on_envvar(xonsh_builtins):
+    env = Env(TEST=0)
+    xonsh_builtins.__xonsh_env__ = env
+    share = []
+    # register
+    @xonsh_builtins.events.on_envvar
+    def handler(name, oldvalue, newvalue, **kwargs):
+        share.extend((name,oldvalue, newvalue))
+
+    # trigger
+    env['TEST'] = 1
+
+    assert share == ['TEST', 0, 1]
+    # assert len(share) > 0 

xonsh/environ.py

@@ -18,6 +18,7 @@ from xonsh import __version__ as XONSH_VERSION
 from xonsh.lazyasd import LazyObject, lazyobject
 from xonsh.codecache import run_script_with_cache
 from xonsh.dirstack import _get_cwd
+from xonsh.events import events
 from xonsh.foreign_shells import load_foreign_envs
 from xonsh.platform import (
     BASH_COMPLETIONS_DEFAULT, DEFAULT_ENCODING, PATH_DEFAULT,
@@ -41,6 +42,11 @@ from xonsh.tools import (
 )
 import xonsh.prompt.base as prompt
 
+events.doc('on_envvar', """
+on_envvar(name: str, oldvalue, newvalue) -> None
+
+Fires after an enviromental variable has changed.
+""")
 
 @lazyobject
 def HELP_TEMPLATE():
@@ -913,6 +919,7 @@ class Env(cabc.MutableMapping):
         ensurer = self.get_ensurer(key)
         if not ensurer.validate(val):
             val = ensurer.convert(val)
+        old_val = self._d.get(key)
         self._d[key] = val
         if self.detypeable(val):
             self._detyped = None
@@ -921,6 +928,7 @@ class Env(cabc.MutableMapping):
                     self.replace_env()
                 else:
                     os.environ[key] = ensurer.detype(val)
+        events.on_envvar.fire(name=key, oldvalue=old_val, newvalue=val)
 
     def __delitem__(self, key):
         val = self._d.pop(key)