Argument 1 has unexpected type 'NoneType'?

Question

I have a problem with my PyQt button action. I would like to send a String with the Function but I got this Error:

TypeError: argument 1 has unexpected type 'NoneType'

import sys
from PyQt5.QtWidgets import QApplication, QPushButton, QAction
from PyQt5.QtCore import QObject, pyqtSignal
from PyQt5.QtGui import *
from PyQt5.uic import *
app = QApplication(sys.argv)
cocktail = loadUi('create.ui')
def mixCocktail(str):
      cocktail.show()
      cocktail.showFullScreen()
      cocktail.lbl_header.setText(str)
widget = loadUi('drinkmixer.ui')
widget.btn_ckt1.clicked.connect(mixCocktail("string"))
widget.show()
sys.exit(app.exec_())

Solution 1

As suggested by user3030010 and ekhumoro it expects a callable function. In which case you should replace that argument with lambda: mixCocktail("string") AND ALSO don't use str it's a python built-in datatype I have replaced it with _str

import sys
from PyQt5.QtWidgets import QApplication, QPushButton, QAction
from PyQt5.QtCore import QObject, pyqtSignal
from PyQt5.QtGui import *
from PyQt5.uic import *
app = QApplication(sys.argv)
cocktail = loadUi('create.ui')
def mixCocktail(_str):
      cocktail.show()
      cocktail.showFullScreen()
      cocktail.lbl_header.setText(_str)
widget = loadUi('drinkmixer.ui')
widget.btn_ckt1.clicked.connect(lambda: mixCocktail("string"))
widget.show()
sys.exit(app.exec_())

More about lambda functions: What is a lambda (function)?

Solution 2

instead of this

widget.btn_ckt1.clicked.connect(mixCocktail("string"))

write

widget.btn_ckt1.clicked.connect(lambda:mixCocktail("string"))

Comments

[user3030010]

From looking at some example online, it looks like it expects a callable function. In which case you should replace that argument with lambda: micCocktail("string")

[ekhumoro]

str is not a keyword - it's a built-in type.

[ekhumoro]

This answer is completely wrong. The correct solution was given in the comment by user3030010.

[harshil9968]

made it wiki as it was from both of your assistance.