How to Avoid Looped Signal Connection Issues in PyQt4?

Connecting Slots and Signals in PyQt4: Resolving Looped Signal Connection Issue

When attempting to connect signals in PyQt4 within a loop, it is common to encounter unexpected behavior such as all buttons printing the same value. This issue stems from the way scoping, name lookup, and closures function in Python.

Within the provided code, the lambda function used for connecting buttons lacks its own binding for the variable i, instead looking up its value in the namespace of the __init__ method. Consequently, i always assumes the last value defined in the loop, which in this case is 9.

To resolve this, Python provides several solutions, including:

Keyword Arguments with Default Value:
By passing i as a keyword argument with a default value, you create a new binding within the lambda function:

self._numberButtons[i].clicked.connect(lambda checked, i=i: self._number(i))

functools.partial:
This provides a more concise and readable approach by wrapping the function call with the desired arguments:

self._numberButtons[i].clicked.connect(partial(self._number, i))

Utilizing these techniques ensures proper binding within each button's callback function, enabling each button to display its corresponding value when clicked.

The above is the detailed content of How to Avoid Looped Signal Connection Issues in PyQt4?. For more information, please follow other related articles on the PHP Chinese website!