Fix empty self-referential variable issue (theskumar#135)

* Show empty self-referential variable issue

theskumar#132

* Correct test names to use interpolation

* Only use previously defined variables when handling interpolation

* Recover original os.environ after tweaking it in a test

dotenv/main.py

@@ -187,7 +187,7 @@ def _replacement(name):
         first search in environ, if not found,
         then look into the dotenv variables
         """
-        ret = os.getenv(name, values.get(name, ""))
+        ret = os.getenv(name, new_values.get(name, ""))
         return ret
 
     def _re_sub_callback(match_object):
@@ -197,10 +197,12 @@ def _re_sub_callback(match_object):
         """
         return _replacement(match_object.group()[2:-1])
 
+    new_values = {}
+
     for k, v in values.items():
-        values[k] = __posix_variable.sub(_re_sub_callback, v)
+        new_values[k] = __posix_variable.sub(_re_sub_callback, v)
 
-    return values
+    return new_values
 
 
 def _walk_to_root(path):

tests/test_core.py

@@ -1,6 +1,7 @@
 # -*- coding: utf-8 -*-
 from __future__ import unicode_literals
 
+import contextlib
 import os
 import pytest
 import tempfile
@@ -13,6 +14,16 @@
 from IPython.terminal.embed import InteractiveShellEmbed
 
 
+@contextlib.contextmanager
+def restore_os_environ():
+    environ = dict(os.environ)
+
+    try:
+        yield
+    finally:
+        os.environ.update(environ)
+
+
 @pytest.mark.parametrize("test_input,expected", [
     ("a=b", ("a", "b")),
     (" a = b ", ("a", "b")),
@@ -161,3 +172,21 @@ def test_dotenv_values_export():
     load_dotenv(stream=stream)
     assert 'foo' in os.environ
     assert os.environ['foo'] == 'bar'
+
+
+def test_dotenv_empty_selfreferential_interpolation():
+    stream = StringIO(u'some_path="${some_path}:a/b/c"\n')
+    stream.seek(0)
+    assert u'some_path' not in os.environ
+    parsed_dict = dotenv_values(stream=stream)
+    assert {u'some_path': u':a/b/c'} == parsed_dict
+
+
+def test_dotenv_nonempty_selfreferential_interpolation():
+    stream = StringIO(u'some_path="${some_path}:a/b/c"\n')
+    stream.seek(0)
+    assert u'some_path' not in os.environ
+    with restore_os_environ():
+        os.environ[u'some_path'] = u'x/y/z'
+        parsed_dict = dotenv_values(stream=stream)
+    assert {u'some_path': u'x/y/z:a/b/c'} == parsed_dict