In PyQt6, QTreeView displays hierarchical data from a model; it does not store that data itself. Use QStandardItemModel for a tree you build in memory, QFileSystemModel for local files and directories, and QSortFilterProxyModel when you need filtering or sorting between a model and the view.
How PyQt6 QTreeView and models work
Qt separates data, presentation, and item interaction. A model exposes data and its hierarchy, a view such as QTreeView displays it, and a delegate handles standard item presentation and editing. The model must represent parent-child relationships for the view to show a tree; setting a flat model on a tree view does not create meaningful hierarchy by itself. This separation also lets one model feed different views without duplicating the underlying data. See the Qt model/view programming tutorial and QTreeView documentation.
Choose a model based on where your data lives:
| Model | Use it when | What it represents |
|---|---|---|
QStandardItemModel |
You are assembling a relatively direct, in-memory tree. | Rows of QStandardItem objects, with text, child rows, checkable state, and other item data. |
A custom QAbstractItemModel subclass |
Your application already owns structured data or needs specialized behavior. | Your own data source, exposed through Qt’s model interface. |
QFileSystemModel |
You want to browse local files and directories. | Local file-system contents. |
Qt for Python documents these standard models and describes QTreeView as a suitable view for file-system content: Model/View Programming overview for Qt for Python.
Build an in-memory tree with QStandardItemModel
This runnable example creates a small, two-level tree. Install a PyQt6 release in your Python environment, save the code as a Python file, and run it. The example uses the PyQt6 Qt Widgets imports and enum spelling shown below.
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import sys
from PyQt6.QtGui import QStandardItem, QStandardItemModel
from PyQt6.QtWidgets import QApplication, QTreeView
app = QApplication(sys.argv)
model = QStandardItemModel()
model.setHorizontalHeaderLabels(["Project"])
frontend = QStandardItem("Frontend")
frontend.appendRow(QStandardItem("Login page"))
frontend.appendRow(QStandardItem("Dashboard"))
backend = QStandardItem("Backend")
backend.appendRow(QStandardItem("Authentication API"))
backend.appendRow(QStandardItem("Reports API"))
model.appendRow(frontend)
model.appendRow(backend)
view = QTreeView()
view.setModel(model)
view.setWindowTitle("Project tasks")
view.resize(420, 300)
view.show()
sys.exit(app.exec())appendRow() adds a top-level item or a child row beneath a parent. The view reads that structure through setModel(). For larger or application-owned data, a custom model can avoid representing the same information again as a second collection of item objects. Qt’s model/view tutorial explains the standard item model and the model interface: Qt model/view programming.
Add model-backed checkboxes
Checkboxes are item state, not a separate feature stored by the view. With standard items, mark an item checkable and initialize its check state. Qt’s item-view machinery and default delegate present and edit that state.
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from PyQt6.QtCore import Qt
from PyQt6.QtGui import QStandardItem
item = QStandardItem("Include generated files")
item.setCheckable(True)
item.setCheckState(Qt.CheckState.Unchecked)
model.appendRow(item)Use Qt.CheckState.Checked instead when the item should start checked. You can read a standard item’s current state with item.checkState(); if you need a view index, read the model’s check-state role for that index.
A custom model must expose check state and accept edits itself. In practical terms, its data implementation returns check-state data for Qt.ItemDataRole.CheckStateRole; its flags mark the relevant item as user-checkable and enabled; and its data-setting implementation handles that role by storing the new state and notifying the view that data changed. Merely drawing a checkbox is not enough if the model does not store updates. Qt’s model/view documentation describes roles, item flags, and standard-item checkbox support: Qt model/view programming tutorial.
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Parent-child checkbox propagation is separate application logic. Checking a parent does not, by itself, establish that all children should be checked, or that a parent should become partially checked when only some children are selected. Implement those rules explicitly if your interface requires them.
Show local files with QFileSystemModel
For a file-browser tree, create a QFileSystemModel, set its root path, and give the model to the view. To show only a chosen directory rather than the model’s broader root, pass the directory’s model index to setRootIndex().
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import sys
from PyQt6.QtCore import QDir
from PyQt6.QtWidgets import QApplication, QFileSystemModel, QTreeView
app = QApplication(sys.argv)
model = QFileSystemModel()
model.setRootPath(QDir.currentPath())
view = QTreeView()
view.setModel(model)
view.setRootIndex(model.index(QDir.currentPath()))
view.setWindowTitle("Current directory")
view.resize(700, 420)
view.show()
sys.exit(app.exec())Here, QDir.currentPath() supplies the directory used for both the model root and the visible tree root. Replace it with another local directory path to browse that location. The model represents file-system information; the tree view provides the familiar expansion and selection interface. Qt’s documented directory example follows the same model-and-view pattern: QTreeView documentation and Qt for Python model/view overview.
Filter a tree from a search field
A QSortFilterProxyModel sits between the source model and the view. The line edit updates the proxy’s filter, while the tree displays the filtered result. This example filters the first column of a standard-item tree, case-insensitively, and uses Qt’s recursive filtering property so a matching descendant can remain visible with its ancestor path. Confirm that the recursive-filtering property is available and behaves as expected in the exact Qt version used by your PyQt6 installation.
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import sys
from PyQt6.QtCore import Qt
from PyQt6.QtGui import QStandardItem, QStandardItemModel
from PyQt6.QtWidgets import (
QApplication,
QLineEdit,
QSortFilterProxyModel,
QTreeView,
QVBoxLayout,
QWidget,
)
app = QApplication(sys.argv)
source = QStandardItemModel()
source.setHorizontalHeaderLabels(["Project"])
for group, tasks in {
"Frontend": ["Login page", "Dashboard"],
"Backend": ["Authentication API", "Reports API"],
}.items():
parent = QStandardItem(group)
for task in tasks:
parent.appendRow(QStandardItem(task))
source.appendRow(parent)
proxy = QSortFilterProxyModel()
proxy.setSourceModel(source)
proxy.setFilterCaseSensitivity(Qt.CaseSensitivity.CaseInsensitive)
proxy.setFilterKeyColumn(0)
proxy.setRecursiveFilteringEnabled(True)
search = QLineEdit()
search.setPlaceholderText("Search projects and tasks")
search.textChanged.connect(proxy.setFilterFixedString)
view = QTreeView()
view.setModel(proxy)
window = QWidget()
layout = QVBoxLayout(window)
layout.addWidget(search)
layout.addWidget(view)
window.setWindowTitle("Search project tasks")
window.resize(460, 340)
window.show()
sys.exit(app.exec())Filtering is also a user-experience decision. Decide whether the search should inspect only a particular column or several, whether matching should be case-sensitive, and whether a matching parent should expose all of its children. The example searches column zero and preserves ancestor paths for descendant matches; it does not define a special rule to reveal every child of a matching parent. Qt documents proxy models as a way to sort or filter another model and supports customizing filtering through subclassing: QSortFilterProxyModel documentation.
If the built-in behavior does not match the desired tree policy, subclass QSortFilterProxyModel and implement filterAcceptsRow() with the required parent and descendant checks. When application code obtains an index from the view while a proxy is installed, that index belongs to the proxy. Use mapToSource() when you need the corresponding source-model index. Qt for Python documents model/view mapping concepts in its Model/View Programming overview.
Choose useful QTreeView behavior
Keep view settings focused on the tree’s task. For example, hide headers for a single-column task hierarchy, expand a selected branch when opening the window, or tune indentation for nested levels. These settings change presentation; they do not change the model’s data.
setHeaderHidden(True)hides the header when column labels are not useful.setIndentation(pixels)adjusts the visual offset of child levels.expand(index)andexpandAll()control which branches are initially open.- Root decoration controls how the root item is drawn; choose it according to whether the root is itself meaningful to users.
- Uniform row heights can help only when every row is guaranteed to have the same height; do not enable the setting if rows can vary.
Sorting is disabled by default for QTreeView. With QStandardItemModel, populate the items first and enable sorting afterward when needed, rather than sorting during every insertion. See QTreeView documentation for view properties and sorting behavior.
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