Prepare support for python 3.8 (#702)

* closes #701

* best practice for handling copmat here is a try..except import

panel/_testing/fixtures.py

@@ -45,7 +45,7 @@ def hv_mpl():
 @pytest.yield_fixture
 def tmpdir(request, tmpdir_factory):
     name = request.node.name
-    name = re.sub("[\W]", "_", name)
+    name = re.sub(r"[\W]", "_", name)
     MAXVAL = 30
     if len(name) > MAXVAL:
         name = name[:MAXVAL]

panel/util.py

@@ -9,9 +9,13 @@
 import numbers
 import datetime as dt
 
-from collections import defaultdict, MutableSequence, MutableMapping, OrderedDict
 from datetime import datetime
 from six import string_types
+from collections import defaultdict, OrderedDict
+try:
+    from collections.abc import MutableSequence, MutableMapping
+except ImportError:  # support for python>3.8
+    from collections import MutableSequence, MutableMapping
 
 import param
 import numpy as np
@@ -77,7 +81,7 @@ def param_name(name):
     """
     Removes the integer id from a Parameterized class name.
     """
-    match = re.match('(.)+(\d){5}', name)
+    match = re.match(r'(.)+(\d){5}', name)
     return name[:-5] if match else name
 
 

panel/viewable.py

@@ -740,7 +740,7 @@ def _cleanup(self, root):
             return
 
         customjs = model.select({'type': CustomJS})
-        pattern = "data\['comm_id'\] = \"(.*)\""
+        pattern = r"data\['comm_id'\] = \"(.*)\""
         for js in customjs:
             comm_ids = list(re.findall(pattern, js.code))
             if not comm_ids: