lambda function in pyqt5 - return None instead of what expected

Question

I'm studying PyQt on the Mark Summerfield book, but using python 3 and PyQt5 I need to convert all the code to the new syntax, and I'm having some problems on this example:

import sys
from functools import partial
from PyQt5.QtCore import *
from PyQt5.QtGui import *
from PyQt5.QtWidgets import *

class Form(QDialog):

    def __init__(self, parent=None):
        super(Form,self).__init__(parent)

        button1 = QPushButton('One')
        button2 = QPushButton('Two')
        button3 = QPushButton('Three')
        button4 = QPushButton('Four')               
        button5 = QPushButton('Five')
        self.label = QLabel('Click a button...')

        layout = QHBoxLayout()
        layout.addWidget(button1)
        layout.addWidget(button2)
        layout.addWidget(button3)
        layout.addWidget(button4)
        layout.addWidget(button5)
        layout.addStretch()
        layout.addWidget(self.label)
        self.setLayout(layout)

        button1.clicked.connect(self.one)

        #partial for passing runtime argument to function, useful for using one slot for many signals
        button2.clicked.connect(partial(self.anyButton,'Two'))

        button3.clicked.connect(lambda who='Three': self.anyButton(who))


    def one(self):
        self.label.setText("You clicked button 'One'")

    def anyButton(self,who):
        self.label.setText("You clicked button '%s'" %who)

app = QApplication(sys.argv)
form = Form()
form.show()
app.exec_()

When I click on button 1 and 2, the program runs as expected, but when I click on button 3 I get this message: "You clicked button 'False'" while I'd expect "You clicked button 'Three'".

So, I think I'm doing something wrong with the syntax of the lambda function, but I can't see what.

Here the original code for pyqt4 and python 2:

self.connect(button3, SIGNAL("clicked()"),lambda who="Three": self.anyButton(who))