Make all Element with Template pickable natively (#144)

* Make _parse_size robust to already parsed values
(needed for unpickling a folium Map)

* Add the _template_str to recover all the Elements

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* __setstate__ simplification

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* More change cleaning, keep only the Element change

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Clean verbosity & set attribute privates

* Remove one action in Element setstate
_template is already in self, no need to update it if not in state.

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

branca/element.py

@@ -57,6 +57,8 @@ def __init__(self, template=None, template_name=None):
         self._env = ENV
         self._children = OrderedDict()
         self._parent = None
+        self._template_str = template
+        self._template_name = template_name
 
         if template is not None:
             self._template = Template(template)
@@ -71,11 +73,18 @@ def __getstate__(self):
         """
         state: dict = self.__dict__.copy()
         state["_env"] = None
+        state.pop("_template", None)
         return state
 
     def __setstate__(self, state: dict):
         """Re-add ._env attribute when unpickling"""
         state["_env"] = ENV
+
+        if state["_template_str"] is not None:
+            state["_template"] = Template(state["_template_str"])
+        elif state["_template_name"] is not None:
+            state["_template"] = ENV.get_template(state["_template_name"])
+
         self.__dict__.update(state)
 
     def get_name(self):