Lazy import of private modules

mdboom · tacaswell · commit 6900a7164b8c · 2019-02-24T14:52:31.000-05:00
diff --git a/doc/api/api_changes.rst b/doc/api/api_changes.rst
@@ -46,6 +46,20 @@ subplotparams will collapse axes to zero width or height.  This prevents
 ``tight_layout`` from being executed.  Similarly
 `.tight_layout.get_tight_layout_figure` will return None.
 
+To improve import (startup) time, private modules are now imported lazily.
+These modules are no longer available at these locations:
+
+  - `matplotlib.backends.backend_agg._png`
+  - `matplotlib.contour._contour`
+  - `matplotlib.image._png`
+  - `matplotlib.mathtext._png`
+  - `matplotlib.testing.compare._png`
+  - `matplotlib.texmanager._png`
+  - `matplotlib.tri.triangulation._tri`
+  - `matplotlib.tri.triangulation._qhull`
+  - `matplotlib.tri.tricontour._tri`
+  - `matplotlib.tri.trifinder._tri`
+
 API Changes for 3.0.0
 =====================
 
diff --git a/lib/matplotlib/backends/backend_agg.py b/lib/matplotlib/backends/backend_agg.py
@@ -38,7 +38,6 @@
 from matplotlib import colors as mcolors
 
 from matplotlib.backends._backend_agg import RendererAgg as _RendererAgg
-from matplotlib import _png
 
 from matplotlib.backend_bases import _has_pil
 
@@ -499,6 +498,7 @@ def print_png(self, filename_or_obj, *args,
             If the 'pnginfo' key is present, it completely overrides
             *metadata*, including the default 'Software' key.
         """
+        from matplotlib import _png
 
         if metadata is None:
             metadata = {}
diff --git a/lib/matplotlib/contour.py b/lib/matplotlib/contour.py
@@ -8,7 +8,6 @@
 from numpy import ma
 
 import matplotlib as mpl
-import matplotlib._contour as _contour
 import matplotlib.path as mpath
 import matplotlib.ticker as ticker
 import matplotlib.cm as cm
@@ -1451,6 +1450,8 @@ def _process_args(self, *args, **kwargs):
             self._mins = args[0]._mins
             self._maxs = args[0]._maxs
         else:
+            import matplotlib._contour as _contour
+
             self._corner_mask = kwargs.pop('corner_mask', None)
             if self._corner_mask is None:
                 self._corner_mask = mpl.rcParams['contour.corner_mask']
diff --git a/lib/matplotlib/image.py b/lib/matplotlib/image.py
@@ -22,7 +22,6 @@
 
 # For clarity, names from _image are given explicitly in this module:
 import matplotlib._image as _image
-import matplotlib._png as _png
 
 # For user convenience, the names from _image are also imported into
 # the image namespace:
@@ -635,6 +634,7 @@ def contains(self, mouseevent):
 
     def write_png(self, fname):
         """Write the image to png file with fname"""
+        from matplotlib import _png
         im = self.to_rgba(self._A[::-1] if self.origin == 'lower' else self._A,
                           bytes=True, norm=True)
         _png.write_png(im, fname)
@@ -1359,7 +1359,11 @@ def imread(fname, format=None):
     .. _Pillow documentation: http://pillow.readthedocs.io/en/latest/
     """
 
-    handlers = {'png': _png.read_png, }
+    def read_png(*args, **kwargs):
+        from matplotlib import _png
+        return _png.read_png(*args, **kwargs)
+
+    handlers = {'png': read_png, }
     if format is None:
         if isinstance(fname, str):
             parsed = urllib.parse.urlparse(fname)
diff --git a/lib/matplotlib/mathtext.py b/lib/matplotlib/mathtext.py
@@ -32,7 +32,7 @@
 
 ParserElement.enablePackrat()
 
-from matplotlib import _png, cbook, colors as mcolors, get_data_path, rcParams
+from matplotlib import cbook, colors as mcolors, get_data_path, rcParams
 from matplotlib.afm import AFM
 from matplotlib.cbook import get_realpath_and_stat
 from matplotlib.ft2font import FT2Image, KERNING_DEFAULT, LOAD_NO_HINTING
@@ -3450,6 +3450,7 @@ def to_png(self, filename, texstr, color='black', dpi=120, fontsize=14):
         Returns the offset of the baseline from the bottom of the
         image in pixels.
         """
+        from matplotlib import _png
         rgba, depth = self.to_rgba(
             texstr, color=color, dpi=dpi, fontsize=fontsize)
         _png.write_png(rgba, filename)
diff --git a/lib/matplotlib/testing/compare.py b/lib/matplotlib/testing/compare.py
@@ -17,7 +17,7 @@
 
 import matplotlib as mpl
 from matplotlib.testing.exceptions import ImageComparisonFailure
-from matplotlib import _png, cbook
+from matplotlib import cbook
 
 __all__ = ['compare_float', 'compare_images', 'comparable_formats']
 
@@ -418,6 +418,8 @@ def compare_images(expected, actual, tol, in_decorator=False):
         compare_images(img1, img2, 0.001)
 
     """
+    from matplotlib import _png
+
     if not os.path.exists(actual):
         raise Exception("Output image %s does not exist." % actual)
 
@@ -488,6 +490,7 @@ def save_diff_image(expected, actual, output):
         File path to save difference image to.
     '''
     # Drop alpha channels, similarly to compare_images.
+    from matplotlib import _png
     expected_image = _png.read_png(expected)[..., :3]
     actual_image = _png.read_png(actual)[..., :3]
     actual_image, expected_image = crop_to_same(
diff --git a/lib/matplotlib/tests/test_basic.py b/lib/matplotlib/tests/test_basic.py
@@ -1,6 +1,9 @@
 import builtins
+import subprocess
+import sys
 
 import matplotlib
+from matplotlib.cbook import dedent
 
 
 def test_simple():
@@ -30,3 +33,24 @@ def test_override_builtins():
                 overridden = True
 
     assert not overridden
+
+
+def test_lazy_imports():
+    source = dedent("""
+    import sys
+
+    import matplotlib.figure
+    import matplotlib.backend_bases
+    import matplotlib.pyplot
+
+    assert 'matplotlib._png' not in sys.modules
+    assert 'matplotlib._tri' not in sys.modules
+    assert 'matplotlib._qhull' not in sys.modules
+    assert 'matplotlib._contour' not in sys.modules
+    """)
+
+    subprocess.check_call([
+        sys.executable,
+        '-c',
+        source
+    ])
diff --git a/lib/matplotlib/texmanager.py b/lib/matplotlib/texmanager.py
@@ -41,7 +41,7 @@
 import numpy as np
 
 import matplotlib as mpl
-from matplotlib import _png, cbook, dviread, rcParams
+from matplotlib import cbook, dviread, rcParams
 
 _log = logging.getLogger(__name__)
 
@@ -397,6 +397,7 @@ def make_png(self, tex, fontsize, dpi):
 
     def get_grey(self, tex, fontsize=None, dpi=None):
         """Return the alpha channel."""
+        from matplotlib import _png
         key = tex, self.get_font_config(), fontsize, dpi
         alpha = self.grey_arrayd.get(key)
         if alpha is None:
diff --git a/lib/matplotlib/tri/triangulation.py b/lib/matplotlib/tri/triangulation.py
@@ -1,8 +1,5 @@
 import numpy as np
 
-import matplotlib._tri as _tri
-import matplotlib._qhull as _qhull
-
 
 class Triangulation(object):
     """
@@ -39,6 +36,8 @@ class Triangulation(object):
     triangles formed from colinear points, or overlapping triangles.
     """
     def __init__(self, x, y, triangles=None, mask=None):
+        from matplotlib import _qhull
+
         self.x = np.asarray(x, dtype=np.float64)
         self.y = np.asarray(y, dtype=np.float64)
         if self.x.shape != self.y.shape or self.x.ndim != 1:
@@ -106,6 +105,7 @@ def get_cpp_triangulation(self):
         Return the underlying C++ Triangulation object, creating it
         if necessary.
         """
+        from matplotlib import _tri
         if self._cpp_triangulation is None:
             self._cpp_triangulation = _tri.Triangulation(
                 self.x, self.y, self.triangles, self.mask, self._edges,
diff --git a/lib/matplotlib/tri/tricontour.py b/lib/matplotlib/tri/tricontour.py
@@ -2,7 +2,6 @@
 
 from matplotlib.contour import ContourSet
 from matplotlib.tri.triangulation import Triangulation
-import matplotlib._tri as _tri
 
 
 class TriContourSet(ContourSet):
@@ -44,6 +43,7 @@ def _process_args(self, *args, **kwargs):
             if self.levels is None:
                 self.levels = args[0].levels
         else:
+            from matplotlib import _tri
             tri, z = self._contour_args(args, kwargs)
             C = _tri.TriContourGenerator(tri.get_cpp_triangulation(), z)
             self._mins = [tri.x.min(), tri.y.min()]
diff --git a/lib/matplotlib/tri/trifinder.py b/lib/matplotlib/tri/trifinder.py
@@ -1,7 +1,6 @@
 import numpy as np
 
 from matplotlib.tri import Triangulation
-import matplotlib._tri as _tri
 
 
 class TriFinder(object):
@@ -35,6 +34,7 @@ class TrapezoidMapTriFinder(TriFinder):
     this should not be relied upon.
     """
     def __init__(self, triangulation):
+        from matplotlib import _tri
         TriFinder.__init__(self, triangulation)
         self._cpp_trifinder = _tri.TrapezoidMapTriFinder(
             triangulation.get_cpp_triangulation())
