Merge pull request #2754 from neutrinoceros/hotfix_mpl3.3_support

hotfix: support matplotlib 3.3.0

yt/utilities/png_writer.py

@@ -1,24 +1,29 @@
 from io import BytesIO
 
-import matplotlib._png as _png
+try:
+    # matplotlib switched from an internal submodule _png to using pillow (PIL)
+    # between v3.1.0 and v3.3.0
+    # So PIL should be available on any system where matplotlib._png doesn't exist
+    import matplotlib._png as _png
+except ImportError:
+    from PIL import Image
 
 
-def call_png_write_png(buffer, width, height, fileobj, dpi):
-    _png.write_png(buffer, fileobj, dpi)
+def call_png_write_png(buffer, fileobj, dpi):
+    try:
+        _png.write_png(buffer, fileobj, dpi)
+    except NameError:
+        Image.fromarray(buffer).save(fileobj, dpi=(dpi, dpi))
 
 
 def write_png(buffer, filename, dpi=100):
-    width = buffer.shape[1]
-    height = buffer.shape[0]
     with open(filename, "wb") as fileobj:
-        call_png_write_png(buffer, width, height, fileobj, dpi)
+        call_png_write_png(buffer, fileobj, dpi)
 
 
-def write_png_to_string(buffer, dpi=100, gray=0):
-    width = buffer.shape[1]
-    height = buffer.shape[0]
+def write_png_to_string(buffer, dpi=100):
     fileobj = BytesIO()
-    call_png_write_png(buffer, width, height, fileobj, dpi)
+    call_png_write_png(buffer, fileobj, dpi)
     png_str = fileobj.getvalue()
     fileobj.close()
     return png_str