Warn when too many figures are opened

Author: mdboom

doc/users/whats_new.rst

@@ -45,6 +45,18 @@ rcParam has been set, and will not retroactively affect already
 existing text objects.  This brings their behavior in line with most
 other rcParams.
 
+Catch opening too many figures using pyplot
+-------------------------------------------
+Figures created through `pyplot.figure` are retained until they are
+explicitly closed.  It is therefore common for new users of matplotlib
+to run out of memory when creating a large series of figures in a
+loop without closing them.
+
+matplotlib will now display a `RuntimeWarning` when too many figures
+have been opened at once.  By default, this is displayed for 20 or
+more figures, but the exact number may be controlled using the
+``figure.max_num_figures`` rcParam.
+
 ``axes.xmargin`` and ``axes.ymargin`` added to rcParams
 -------------------------------------------------------
 ``rcParam`` values (``axes.xmargin`` and ``axes.ymargin``) were added
@@ -111,7 +123,7 @@ conversion (`mpl.rc('svg', fonttype='none')`).
 More robust boxplots
 --------------------
 Paul Hobson provided a fix to the :func:`~matplotlib.pyplot.boxplot`
-method that prevent whiskers from being drawn inside the box for 
+method that prevent whiskers from being drawn inside the box for
 oddly distributed data sets.
 
 Triangular grid interpolation

lib/matplotlib/pyplot.py

@@ -394,6 +394,17 @@ def figure(num=None,  # autoincrement if None, else integer from 1-N
 
     figManager = _pylab_helpers.Gcf.get_fig_manager(num)
     if figManager is None:
+        max_num_figures = rcParams['figure.max_num_figures']
+
+        if (max_num_figures >= 1 and
+            len(allnums) >= max_num_figures):
+            warnings.warn(
+                "More than %d figures have been opened.  Figures created "
+                "through the pyplot interface are retained until explicitly "
+                "closed.  (To control this warning, see the rcParam "
+                "'figure.max_num_figures'." %
+                max_num_figures, RuntimeWarning)
+
         if get_backend().lower() == 'ps':
             dpi = 72
 

lib/matplotlib/rcsetup.py

@@ -680,6 +680,7 @@ def __call__(self, s):
     'figure.edgecolor':  ['w', validate_color],  # edgecolor; white
     'figure.frameon':    [True, validate_bool],
     'figure.autolayout': [False, validate_bool],
+    'figure.max_num_figures': [20, validate_int],
 
     'figure.subplot.left': [0.125, ValidateInterval(0, 1, closedmin=True,
                                                        closedmax=True)],

lib/matplotlib/tests/test_figure.py

@@ -1,4 +1,4 @@
-from nose.tools import assert_equal, assert_true
+from nose.tools import assert_equal, assert_true, assert_raises
 from matplotlib.testing.decorators import image_comparison, cleanup
 import matplotlib.pyplot as plt
 
@@ -92,6 +92,15 @@ def test_alpha():
                                               alpha=0.6,
                                               facecolor='red'))
 
+@cleanup
+def test_too_many_figures():
+    import warnings
+
+    with warnings.catch_warnings(record=True) as w:
+        for i in range(22):
+            fig = plt.figure()
+    assert len(w) == 1
+
 
 if __name__ == "__main__":
     import nose

matplotlibrc.template

@@ -318,6 +318,9 @@ text.hinting_factor : 8 # Specifies the amount of softness for hinting in the
 #figure.edgecolor : white   # figure edgecolor
 #figure.autolayout : False  # When True, automatically adjust subplot
                             # parameters to make the plot fit the figure
+#figure.max_num_figures : 20  # The maximum number of figures to open through
+                              # the pyplot interface.  If less than one,
+                              # there is no maximum.
 
 # The figure subplot parameters.  All dimensions are a fraction of the
 # figure width or height