Add a callback system

README.md

@@ -19,6 +19,7 @@ pip install mpl-image-labeller
 - Displays images with correct aspect ratio
 - Easily configurable keymap
 - Smart interactions with default Matplotlib keymap
+- Callback System (see `examples/callbacks.py`)
 
 ![gif of usage for labelling images of cats and dogs](example.gif)
 

examples/callbacks.py

@@ -0,0 +1,21 @@
+import matplotlib.pyplot as plt
+import numpy as np
+
+from mpl_image_labeller import image_labeller
+
+images = np.random.randn(5, 10, 10)
+labeller = image_labeller(images, classes=["good", "bad", "blarg"])
+
+
+def image_changed_callback(index, image):
+    print(index)
+    print(image.sum())
+
+
+def label_assigned(index, label):
+    print(f"label {label} assigned to image {index}")
+
+
+labeller.on_image_changed(image_changed_callback)
+labeller.on_label_assigned(image_changed_callback)
+plt.show()

mpl_image_labeller/_labeller.py

@@ -2,6 +2,7 @@
 
 import numpy as np
 from matplotlib.backend_bases import key_press_handler
+from matplotlib.cbook import CallbackRegistry
 from matplotlib.figure import Figure
 
 
@@ -155,6 +156,7 @@ def _get_image(i):
         )
 
         self._fig.canvas.mpl_connect("key_press_event", self._key_press)
+        self._observers = CallbackRegistry()
 
     @property
     def ax(self):
@@ -205,6 +207,7 @@ def _update_displayed(self):
         self._im.set_data(image)
         self._im.set_extent((-0.5, image.shape[1] - 0.5, image.shape[0] - 0.5, -0.5))
         self._update_title()
+        self._observers.process("image-changed", self._image_index, image)
         self._fig.canvas.draw_idle()
 
     def _key_press(self, event):
@@ -213,9 +216,9 @@ def _key_press(self, event):
         elif event.key == "right":
             self.image_index += 1
         elif event.key in self._label_keymap:
-            self._labels[self._image_index] = self._classes[
-                self._label_keymap[event.key]
-            ]
+            klass = self._classes[self._label_keymap[event.key]]
+            self._labels[self._image_index] = klass
+            self._observers.process("label-assigned", self._image_index, klass)
             if self._label_advances:
                 if self.image_index == self._N_images - 1:
                     # make sure we update the title we are on the last image
@@ -228,3 +231,41 @@ def _key_press(self, event):
                 self._update_title()
                 # TODO: blit just the text here
                 self._fig.canvas.draw_idle()
+
+    def on_label_assigned(self, func):
+        """
+        Connect *func* as a callback function for when a label is assigned
+        to an image. *func* will receive the index of the image and the
+        new class.
+
+        Parameters
+        ----------
+        func : callable
+            Function to call when a point is added.
+
+        Returns
+        -------
+        int
+            Connection id (which can be used to disconnect *func*).
+        """
+        return self._observers.connect("label-assigned", lambda *args: func(*args))
+
+    def on_image_changed(self, func):
+        """
+        Connect *func* as a callback function for when the displayed image
+        is changed. *func* will receive the index of the new image and the
+        image. `fig.canvas.draw_idle` will be called after the callback is
+        executed so if you are modifying the figure then you do not need to
+        explicitly call *draw* yourself.
+
+        Parameters
+        ----------
+        func : callable
+            Function to call when a point is added.
+
+        Returns
+        -------
+        int
+            Connection id (which can be used to disconnect *func*).
+        """
+        return self._observers.connect("image-changed", lambda *args: func(*args))