fix reference losing for _pipfile

pipenv/patched/contoml/file/file.py

@@ -271,6 +271,18 @@ class TOMLFile:
     def elements(self):
         return self._elements
 
+    _marker = object()
+
+    def pop(self, item, default=_marker):
+        """Pops an item and return the value"""
+        if item in self:
+            rv = self[item]
+            del self[item]
+            return rv
+        if default is self._marker:
+            raise KeyError(item)
+        return default
+
     def __str__(self):
 
         is_empty = (not self['']) and (not tuple(k for k in self.keys() if k))

pipenv/project.py

@@ -377,7 +377,7 @@ class Project(object):
         # mutation time!
         self.clear_pipfile_cache()
         for section in ('packages', 'dev-packages'):
-            p_section = dict(pfile.get(section, {}))
+            p_section = pfile.get(section, {})
             for key in list(p_section.keys()):
                 # Normalize key name to PEP 423.
                 norm_key = pep423_name(key)