Avoid repeatedly warning about too many figures open.

anntzer · anntzer · commit fa53aa3ecd62 · 2020-01-24T09:35:13.000+01:00
Warning once is useful, but no need to warn again if the user
further creates even more figure later in their code (see e.g.
tutorials/intermediate/constrainedlayout_guide.py which spams the
terminal with such warnings).

(Yes, the warning would still get reemitted if the user closes some
windows and then goes again above the limit -- that's less of an issue
and not really worth working around IMO.)
diff --git a/lib/matplotlib/pyplot.py b/lib/matplotlib/pyplot.py
@@ -503,7 +503,7 @@ def figure(num=None,  # autoincrement if None, else integer from 1-N
     if figManager is None:
         max_open_warning = rcParams['figure.max_open_warning']
 
-        if len(allnums) >= max_open_warning >= 1:
+        if len(allnums) == max_open_warning >= 1:
             cbook._warn_external(
                 "More than %d figures have been opened. Figures "
                 "created through the pyplot interface "
