How to keep the widget when use QSortFilterProxyModel?

Question

I'm making a bulletin board using a table view now. Here, the proxy model is used for the search function, and all contents are well output. However, I want to insert listwidget for the attached file part, but it doesn't work well. First, the width disappears after searching. Second, I want to set the size of the listwidget to the size inherited from the internal row.

Normal [![enter image description here][1]][1]

Search and Reset(delete search keyword)

[![enter image description here][2]][2]

↑ If you search and reset it, the widget is gone.

from PyQt5.QtWidgets import *
from PyQt5.QtCore import *
from PyQt5.QtGui import *

class Buttons(QWidget):
    def __init__(self):
        super().__init__()
        layout = QHBoxLayout(self)
        layout.addWidget(QPushButton('btn1'))
        layout.addWidget(QPushButton('btn2'))
        self.setLayout(layout)

class MainWindow(QWidget):

    def __init__(self, *args, **kwargs):
        super(MainWindow, self).__init__(*args, **kwargs)
        self.setGeometry(200,200,1000,1000)
        self.tab = QTableView()
        self.sti = QStandardItemModel()
        self.sti.setHorizontalHeaderLabels(["Date","Name","Content","Attach"])

        proxy = QSortFilterProxyModel()
        proxy.setSourceModel(self.sti)
        proxy.setFilterKeyColumn(-1)
        searchbar=QLineEdit()
        searchbar.textChanged.connect(proxy.setFilterRegExp)

        self.tab.setModel(proxy)
        self.tab.setEditTriggers(QAbstractItemView.NoEditTriggers)
        self.tab.verticalHeader().setSectionResizeMode(QHeaderView.ResizeToContents)
        self.get_list()

        layout = QVBoxLayout()
        layout.addWidget(searchbar)
        layout.addWidget(self.tab)

        self.setLayout(layout)

    def get_list(self):
        data = {
            'Date': [2016, 2017, 2018],
            'Name': [2.8, 3.1, 3.0],
            'Content': ['aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa', '1.73M', '1.83M'],
            'Attach':[[1,2],[3,4],[5,6]]
        }
        df = pd.DataFrame(data)
        for i in range(len(df.index)):
            for j in range(len(df.columns)):
                item = QStandardItem(str(df.iloc[i,j]))
                item.setFlags(item.flags() ^ Qt.ItemIsEditable)
                self.sti.setItem(i,j,item)
                # attachment list
                if j == 3:
                    list = QListWidget()
                    list.insertItem(0,"www.google.com/attach1")
                    list.insertItem(1, "www.google.com/attach1")
                    list.insertItem(2, "www.google.com/attach1")
                    list.insertItem(3, "www.google.com/attach1")
                    self.tab.setIndexWidget(self.tab.model().index(i,j),list)


app = QApplication([])
window = MainWindow()
window.resize(800, 600)
window.show()
app.exec_() ```


  [1]: https://i.stack.imgur.com/xSdaR.png
  [2]: https://i.stack.imgur.com/XZxoY.png