PyQt widget alignment with other elements

Question

Consider this small GUI example that is supposed to display two GroupBoxes. The first one is placed in a custom QWidget:

import sys
from PyQt4 import QtGui

class SomeBoxWidget(QtGui.QWidget):
    def __init__(self):
        super(SomeBoxWidget, self).__init__()

        #create GroupBox and layout
        self.group_box = QtGui.QGroupBox("group box in widget")
        self.group_box_layout = QtGui.QVBoxLayout()
        self.group_box.setLayout(self.group_box_layout)

        #place some stuff there
        self.btn = QtGui.QPushButton("button", self)
        self.group_box_layout.addWidget(self.btn)

        self.main_layout = QtGui.QVBoxLayout()
        self.main_layout.addWidget(self.group_box)
        self.setLayout(self.main_layout)

This QWidget is placed next to a second QGroupBox that is placed directly into the main GUI layout:

class SomeGui(QtGui.QWidget):

    def __init__(self):
        super(SomeGui, self).__init__()

        #create 2nd GroupBox and layout
        self.group_box = QtGui.QGroupBox("group box in layout")
        self.group_box_layout = QtGui.QVBoxLayout()
        self.group_box.setLayout(self.group_box_layout)

        self.btn = QtGui.QPushButton("button", self)
        self.group = SomeBoxWidget()

        self.group_box_layout.addWidget(self.btn)

        self.main_layout = QtGui.QVBoxLayout()
        self.main_layout.addWidget(self.group_box)
        self.main_layout.addWidget(self.group)

        self.setLayout(self.main_layout)

        self.show()

def main():
    app = QtGui.QApplication(sys.argv)
    ex = SomeGui()
    app.exec_()        

if __name__ == '__main__':
    main()

You will notice that both QGroupBoxes are not aligned, I assume because the first one is placed inside a QWidget. How can I align them keeping the first box inside the Widget? If possible, without setting default fixed hight/width values somewhow.

Edit: I assume I need something like setContensMargins but for the outer area...

Answer 1

You could set the content margins of the layout of your SomeBoxWidget container widget to 0 by adding this in your class __init__:

self.main_layout.setContentsMargins(0, 0, 0, 0)

where the arguments of setContentsMargins are respectively the left, top, right, and bottom margins of the layout. According to the documentation:

By default, QLayout uses the values provided by the style. On most platforms, the margin is 11 pixels in all directions.

Doing the above in the code you provided results in: