Fix deprecation warning with Python >= 3.7.

Python >= 3.7 issues a deprecation warning when using collections.Callable
rather than collections.abc.Callable.  Most of Beautiful Soup deals with
this by using a conditional import, but the automatic Python 3 conversion
apparently translates `callable(obj)` to `isinstance(obj,
collections.Callable)` which trips this deprecation warning.

`isinstance(obj, Callable)` works fine in Python 2 as well as 3, so just use
it directly.

1 files changed, 1 insertions, 1 deletions

diff --git a/bs4/element.py b/bs4/element.py
index 2001ad5..8684870 100644
--- a/bs4/element.py
+++ b/bs4/element.py
@@ -163,7 +163,7 @@ class PageElement(object):
             c = XMLFormatter
         else:
             c = HTMLFormatter
-        if callable(formatter):
+        if isinstance(formatter, Callable):
             return c(entity_substitution=formatter)
         return c.REGISTRY[formatter]