import matplotlib lazily

Loading the relevant dependencies from matplotlib takes multiple second.

There would seem to be no justification in importing matplotlib before we know whether an --mpl-* option is used, but we can even delay import until the individual tests, adding little overhead.

Author: jnothman

pytest_mpl/plugin.py

@@ -39,20 +39,12 @@
 
 import pytest
 
-import matplotlib
-import matplotlib.pyplot as plt
-from matplotlib.testing.compare import compare_images
-from matplotlib.testing.decorators import ImageComparisonTest as MplImageComparisonTest
-
 if sys.version_info[0] == 2:
     from urllib import urlopen
 else:
     from urllib.request import urlopen
 
 
-MPL_LT_15 = LooseVersion(matplotlib.__version__) < LooseVersion('1.5')
-
-
 def _download_file(url):
     u = urlopen(url)
     result_dir = tempfile.mkdtemp()
@@ -115,6 +107,13 @@ def __init__(self, config, baseline_dir=None, generate_dir=None, results_dir=Non
 
     def pytest_runtest_setup(self, item):
 
+        import matplotlib
+        import matplotlib.pyplot as plt
+        from matplotlib.testing.compare import compare_images
+        from matplotlib.testing.decorators import ImageComparisonTest as MplImageComparisonTest
+
+        MPL_LT_15 = LooseVersion(matplotlib.__version__) < LooseVersion('1.5')
+
         compare = item.keywords.get('mpl_image_compare')
 
         if compare is None: