applets: add plot_hist dataset length mismatch warning (#1718)

artiq/applets/plot_hist.py

@@ -1,6 +1,7 @@
 #!/usr/bin/env python3
 
-import PyQt5  # make sure pyqtgraph imports Qt5
+import PyQt5    # make sure pyqtgraph imports Qt5
+from PyQt5.QtCore import QTimer
 import pyqtgraph
 
 from artiq.applets.simple import TitleApplet
@@ -10,6 +11,9 @@ class HistogramPlot(pyqtgraph.PlotWidget):
     def __init__(self, args):
         pyqtgraph.PlotWidget.__init__(self)
         self.args = args
+        self.timer = QTimer()
+        self.timer.setSingleShot(True)
+        self.timer.timeout.connect(self.length_warning)
 
     def data_changed(self, data, mods, title):
         try:
@@ -24,10 +28,19 @@ class HistogramPlot(pyqtgraph.PlotWidget):
             x = list(range(len(y)+1))
 
         if len(y) and len(x) == len(y) + 1:
+            self.timer.stop()
             self.clear()
             self.plot(x, y, stepMode=True, fillLevel=0,
                       brush=(0, 0, 255, 150))
             self.setTitle(title)
+        else:
+            self.timer.start(1000)
+
+    def length_warning(self):
+        self.clear()
+        text = "⚠️ dataset lengths mismatch:\n"\
+            "There should be one more bin boundaries than there are Y values"
+        self.addItem(pyqtgraph.TextItem(text))
 
 
 def main():