QObject.connect silently fails when connected to method of instance not stored in variable

from PySide.QtCore import *
from PySide.QtGui import *

class Connector(object):
    def __init__(self):
        button.clicked.connect(self.slot)

    def slot(self):
        print 'Clicked'

app = QApplication(())
button = QPushButton('Press me')
Connector()
button.show()
app.exec_()

from PySide.QtCore import *
from PySide.QtGui import *

class Connector(object):
    def __init__(self):
        # `self.slot` -> `lambda: self.slot()`
        button.clicked.connect(lambda: self.slot())

    def slot(self):
        print 'Clicked'

app = QApplication(())
button = QPushButton('Press me')
Connector()
button.show()
app.exec_()