allow qt_plugin imsave() function to write to file-like objects

skimage/io/_plugins/qt_plugin.py

@@ -7,8 +7,8 @@ import sys
 window_manager.acquire('qt')
 
 try:
-    from PyQt4.QtGui import (QApplication, QMainWindow, QImage, QPixmap,
-                             QLabel, QWidget)
+    from PyQt4.QtGui import (QApplication, QImage,
+                             QLabel, QMainWindow, QPixmap, QWidget)
     from PyQt4 import QtCore, QtGui
     import sip
     import warnings
@@ -148,12 +148,21 @@ def _app_show():
         print 'No images to show.  See `imshow`.'
 
 
-def imsave(filename, img):
+def imsave(filename, img, format_str=None):
     # we can add support for other than 3D uint8 here...
     img = prepare_for_display(img)
     qimg = QImage(img.data, img.shape[1], img.shape[0],
                           img.strides[0], QImage.Format_RGB888)
-    saved = qimg.save(filename)
+    if _is_filelike(filename):
+        byte_array = QtCore.QByteArray()
+        qbuffer = QtCore.QBuffer()
+        qbuffer.open(QtCore.QIODevice.ReadWrite)
+        saved = qimg.save(qbuffer, format_str.upper())
+        qbuffer.seek(0)
+        filename.write(qbuffer.readAll())
+        qbuffer.close()
+    else:
+        saved = qimg.save(filename)
     if not saved:
         from textwrap import dedent
         msg = dedent(
@@ -161,3 +170,7 @@ def imsave(filename, img):
             for the QT imsave plugin are:
             BMP, JPG, JPEG, PNG, PPM, TIFF, XBM, XPM''')
         raise RuntimeError(msg)
+
+
+def _is_filelike(possible_filelike):
+    return callable(getattr(possible_filelike, 'write', None))