lst_f = QtGui.QFontDatabase()
lst_f.families()
print(lst_f)

        
...
        lst_f = QtGui.QFontDatabase()
        font_list = lst_f.families()
        print(font_list)
...
>>>
['Aharoni', 'Algerian', 'Andalus'....., 'Wingdings 3']

 <PyQt4.QtGui.QFontDatabase object at 0x7f554c09a908>

 # Python 3. PyQt4
# -*- coding: utf-8 -*-
import sys
from PyQt4 import QtGui, QtCore
# ГРАФИКА
class Window(QtGui.QWidget):
    def __init__(self, parent=None):
        QtGui.QWidget.__init__(self, parent)
        self.resize(200, 50) # шир / выс окна         
# БЛОК РАЗМЕТКИ
        self.vbox = QtGui.QVBoxLayout()
        # ---
        self.btn = QtGui.QPushButton('Пуск')
        self.btn.clicked.connect(self.on_click)
        self.vbox.addWidget(self.btn)
        # ---
        self.setLayout(self.vbox)
    # ЛОГИКА
    
    def on_click (self):
        lst_f = QtGui.QFontDatabase()
        lst_f.families()
        print(lst_f)
# КОНЕЦ
if __name__ == "__main__":
    app = QtGui.QApplication(sys.argv)
    window = Window()   
    window.show()
    sys.exit(app.exec_())

 ['Aharoni', 'Algerian', 'Andalus'....., 'Wingdings 3']