Qt5NumberValidator.py

import sys

from PyQt5 import QtCore, QtGui, QtWidgets

class Test(QtWidgets.QWidget):
    
    def __init__(self):
        super(Test, self).__init__()
        self.setObjectName("self")
        self.resize(400, 41)
        self.lineEdit = QtWidgets.QLineEdit(self)
        self.lineEdit.setGeometry(QtCore.QRect(10, 10, 381, 22))
        self.lineEdit.setObjectName("lineEdit")
        
        # Vincular el cambio de texto del campo
        self.lineEdit.textChanged.connect(self.validator)
        
        self.retranslateUi()
        QtCore.QMetaObject.connectSlotsByName(self)
    
    def validator(self):
        
        pos = '0123456789.-'
        t = self.sender().text()
        
        if(len(t) > 0):
            # Caracteres posibles
            if(t[-1] not in pos):
                t = t[:-1]
        
        if(len(t) > 0):
            # Validar un solo - al inicio
            if( (t[-1] == '-' and '-' in t[:-1]) or (t[-1] == '-' and len(t) > 1) ):
                t = t[:-1]
                
        if(len(t) > 0):
            # Validar un solo .
            if(t[-1] == '.' and '.' in t[:-1]):
                t = t[:-1]
            
        self.sender().setText(t)
    
    def retranslateUi(self):
        _translate = QtCore.QCoreApplication.translate
        self.setWindowTitle(_translate("self", "self"))

app = QtWidgets.QApplication(sys.argv)
t = Test()
t.show()
sys.exit(app.exec_())