Qt5 cannot set sizes from float values, so we must calculate with integer division
Index: pampi/pampi/libs/main.py
===================================================================
--- pampi.orig/pampi/libs/main.py
+++ pampi/pampi/libs/main.py
@@ -128,7 +128,7 @@ class MainWindow(QtWidgets.QMainWindow,
         self.updateWindowTitle()
         self.updateLastFilesMenu()
         rect = QtWidgets.QApplication.desktop().availableGeometry()
-        self.resize(3 * rect.width() / 4, 3 * rect.height() / 4)
+        self.resize(3 * rect.width() // 4, 3 * rect.height() // 4)
         self.showHelp(here=True)
         self.markdownEditor.setFocus()
         self.loadPlugins()
@@ -179,13 +179,13 @@ class MainWindow(QtWidgets.QMainWindow,
         lines = utils_filesdirs.readTextFile(self.examplesFile)        
         self.samplesEditor.setPlainText(lines)
         rect = QtWidgets.QApplication.desktop().availableGeometry()
-        self.hsplitter.setSizes([rect.width() / 3, rect.width() / 2])
+        self.hsplitter.setSizes([rect.width() // 3, rect.width() // 2])
         self.closing = False
         self.createActions()
         self.createMenusAndButtons()
 
         # Barre d'outils en haut, pour les plugins
-        self.pluginsWidget.setMinimumHeight(1.5 * utils.STYLE['PM_ToolBarIconSize'])
+        self.pluginsWidget.setMinimumHeight(int(1.5 * utils.STYLE['PM_ToolBarIconSize']))
         #self.pluginToolBar = QtWidgets.QToolBar(self)
         self.pluginToolBar = QtWidgets.QToolBar(self.pluginsWidget)
         self.pluginToolBar.setIconSize(iconsize)