[PyQt] What is difference between "partial" and "lambda" in connect slot?

[bluekyu]

Hello. I have a question about "partial" and "lambda" in connect slot.

I learned that "partial" and "lambda" can have arguments in connect slot.
So, I usually use lambda function, however, it does not work well in 
some code.

My example code:
--------------------------------------------
from PyQt4.QtCore import *
from PyQt4.QtGui import *
import sys
from functools import partial

app = QApplication(sys.argv)
form = QDialog()
layout = QVBoxLayout()

label = QLabel("Test")
layout.addWidget(label)

stringList = ["ABC", "123", "XYZ", "789"]
for string in stringList:
     button = QPushButton(string)
     layout.addWidget(button)
     form.connect(button, SIGNAL("clicked()"),
#                    lambda: label.setText(string))    # Problem
                     partial(label.setText, string))

form.setLayout(layout)
form.show()
app.exec_()
---------------------------------------------

I expected that each button set label text as each string, but all 
button set label text as "789".
Instead, partial function works very well.

What is difference between "partial" and "lambda"?