flake8-qgis 2.0.0

Flake8 plugin for QGIS python plugins.

flake8-qgis

A flake8 plugin for QGIS3 python plugins written in Python.

Made with Cookiecutter template cookiecutter-flake8-plugin. Inspired by flake8-simplify.

Installation

Install with pip:

pip install flake8-qgis

Usage

Just call flake8 . in your package or flake your.py.

Rules

Rule	Description
QGS101	Avoid using from-imports from qgis protected members
QGS102	Avoid using imports from qgis protected members
QGS103	Avoid using from-imports from PyQt directly
QGS104	Avoid using imports from PyQt directly
QGS105	Avoid passing QgisInterface as an argument
QGS106	Avoid importing gdal directly, import it from osgeo package
QGS107	Use 'exec' instead of 'exec_'
QGS108	Use QgsProcessing.TEMPORARY_OUTPUT instead of "TEMPORARY_OUTPUT"
QGS109	Use QgsProcessing.TEMPORARY_OUTPUT instead of misspelled "TEMPORARY_OUTPUT"
QGS110	Use is_child_algorithm=True when running other algorithms in the plugin
QGS201	Check return values from a probable PyQgs method call
QGS202	Check return values from a possible PyQgs method call
QGS401	Use 'QApplication.instance()' instead of 'qApp'
QGS402	Use 'QMetaType.Type.X' instead of 'QVariant.X'
QGS403	Used enum has been removed in Qt6
QGS404	QFontMetrics.width() has been removed in Qt6
QGS405	QComboBox activated[str] has been removed in Qt6
QGS406	QRegExp has been removed in Qt6, use QRegularExpression instead
QGS407	QDesktopWidget has been removed in Qt6
QGS408	Support for compiled resources has been removed in PyQt6
QGS409	Fragile call to addAction
QGS410	Use NULL instead of QVariant()
QGS411	QDateTime(yyyy, mm, dd, hh, MM, ss, ms, ts) doesn't work anymore in Qt6
QGS412	QDateTime(QDate(...)) doesn't work anymore in Qt6

Please check the Examples section below for good and bad usage examples for each rule.

While it's important to adhere to these rules, there might be good reasons to ignore some of them. You can do so by using the standard Flake8 configuration. For example, in the setup.cfg file:

[flake8]
ignore = QGS101, QGS102

If you only want to support QGIS 3, you can put:

[tool.flake8]
# Select QGIS3 compatible rules
select = ["QGS1"]

QGS101

Avoid using from-imports from qgis protected members

An exception is made for importing qgis._3d (since flake-qgis 1.1.0). The underscore in the package name is used to prevent the name from starting with a number, ensuring it is a valid package name.

Why is this bad?

Protected members are potentially unstable across software versions. Future changes in protected members might cause problems.

Example

# Bad
from qgis._core import QgsMapLayer, QgsVectorLayer
from qgis._core import QgsApplication

# Good
from qgis.core import QgsMapLayer, QgsVectorLayer
from qgis.core import QgsApplication

QGS102

Avoid using imports from qgis protected members

An exception is made for importing qgis._3d (since flake-qgis 1.1.0). The underscore in the package name is used to prevent the name from starting with a number, ensuring it is a valid package name.

Why is this bad?

Protected members are potentially unstable across software versions. Future changes in protected members might cause problems.

Example

# Bad
import qgis._core.QgsVectorLayer as QgsVectorLayer

# Good
import qgis.core.QgsVectorLayer as QgsVectorLayer

QGS103

Avoid using from-imports from PyQt directly

Why is this bad?

Importing directly from PyQt might create conflict with QGIS bundled PyQt version

Example

# Bad
from PyQt5.QtCore import pyqtSignal

# Good
from qgis.PyQt.QtCore import pyqtSignal

QGS104

Avoid using imports from PyQt directly

Why is this bad?

Importing directly from PyQt might create conflict with QGIS bundled PyQt version

Example

# Bad
import PyQt5.QtCore.pyqtSignal as pyqtSignal

# Good
import qgis.PyQt.QtCore.pyqtSignal as pyqtSignal

QGS105

Avoid passing QgisInterface as an argument

Why is this bad?

It is much easier to import QgisInterface, and it's easier to mock it as well when writing tests. This approach is not however documented properly, so the API might change at some point to exclude this.

This rule can be excluded safely since this is only a matter of preference. Passing iface as an argument is the documented way of getting QgisInterface in plugins. However, it requires writing more code.

Example

# Bad: iface passed as argument
def some_function(somearg, iface):
    # do something with iface


# Good: iface imported
from qgis.utils import iface

def some_function(somearg):
    # do something with iface

# in classFactory the passing is OK, since QGIS injects it
def classFactory(iface):
    # preferably do not pass the iface to plugin

QGS106

Avoid importing gdal directly, import it from osgeo package

Why is this bad?

Importing directly from gdal might create conflict with different gdal versions

Example

# Bad
import gdal
import ogr

# Good
from osgeo import gdal

QGS107

Use 'exec' instead of 'exec_'

Why is this bad?

exec_ was introduced in PyQt to avoid conflict with Python 2.7 exec keyword. Keyword exec was removed in Python 3.0 and exec_ was removed in later PyQt versions.

Example

# Bad
window.exec_()

# Good
window.exec()

QGS108

Use QgsProcessing.TEMPORARY_OUTPUT instead of "TEMPORARY_OUTPUT"

Why is this bad?

It is a good practice to use the constant that PyQGIS API provides.

Example

# Bad
output = "TEMPORARY_OUTPUT"

# Good
from qgis.core import QgsProcessing
output = QgsProcessing.TEMPORARY_OUTPUT

QGS109

Use QgsProcessing.TEMPORARY_OUTPUT instead of misspelled "TEMPORARY_OUTPUT"

Why is this bad?

It is a good practice to use the constant that PyQGIS API provides.

Example

# Bad
output = "TEMPRARY_OUTPUT"

# Good
from qgis.core import QgsProcessing
output = QgsProcessing.TEMPORARY_OUTPUT

QGS110

Use is_child_algorithm=True when running other algorithms in the plugin

Why is this bad?

This rule applies to all algorithms that run other algorithms. Feel free to ignore the rule if you are just running an algorithm in your plugin.

Ensuring the algorithm is run as a child algorithm will help to avoid crashes and otherwise surprising behavior.

Example

# Bad
# In your own algorithm
processing.run("native:buffer", {"INPUT": layer})

# Good
# In your own algorithm
processing.run("native:buffer", {"INPUT": layer}, is_child_algorithm=True)

QGS201

Check return values from a probable PyQgs method call.

A method is determined to be probably a PyQgs method with the following logic:

• It appears on the qgis_return_methods.json list
• The corresponding class is imported in the same file

Feel free to ignore this rule for lines that are not relevant.

[!WARNING] This rule is considered experimental, feel free to ignore it. All feedback is much appreciated!

Why is this bad?

Some PyQgs methods return a success flag and or an error message. Ignoring the return value can hide errors and skip the message.

Example

# Bad
from qgis.core import QgsProject

project.writeToFile("project.qgz")

# Good
from qgis.core import QgsProject

ok, msg = project.writeToFile("project.qgz")
if not ok:
    raise RuntimeError(msg)

QGS202

Check return values from a possible PyQgs method call.

A method is determined to be possibly a PyQgs method with the following logic:

• It appears on the qgis_return_methods.json list
• The method has uppercase characters in its name

Since the corresponding class does not have to be imported in the same file, this rule might have lot of false positives. Feel free to ignore this rule for lines that are not relevant.

[!WARNING] This rule is considered experimental, feel free to ignore it. All feedback is much appreciated!

Why is this bad?

Some PyQgs methods return a success flag and or an error message. Ignoring the return value can hide errors and skip the message.

Example

# Bad
project.addMapLayer(layer)

# Good
added_layer = project.addMapLayer(layer)
if added_layer is None:
    raise RuntimeError("Layer could not be added")

QGIS 4 compatibility rules

QGS401

Use 'QApplication.instance()' instead of 'qApp'

Why is this bad?

qApp has been removed from Qt6 api.

Example

# Bad
qgis.PyQt.QtWidgets import qApp

qApp.processEvents()

# Good
qgis.PyQt.QtWidgets import QApplication

QApplication.instance().processEvents()

QGS402

Use 'QMetaType.Type.X' instead of 'QVariant.X'. Rule also suggests renaming if neccessary.

[!CAUTION] After fixing these warnings, the plugin may not be compatible with QGIS 3 versions so feel free to ignore this rule and come up with another solution it if you want to support both.

Why is this bad?

QVariant.Type has been removed from Qt6 api.

Example

# Bad
QVariant.Int
QVariant.String

# Good
QMetaType.Int
QMetaType.QString

QGS403

Use 'X' enum instead of removed 'Y'.

Why is this bad?

Lot of enums have been refactored in Qt6 api.

Example

# Bad
Qt.MidButton

# Good
Qt.MouseButton.MiddleButton

QGS404

QFontMetrics.width() has been removed in Qt6. Use QFontMetrics.horizontalAdvance() or QFontMetrics.boundingRect().width() instead.

Why is this bad?

QFontMetrics.width was removed from Qt6 api.

Example

# Bad
QFontMetrics.width()

# Good
QFontMetrics.horizontalAdvance()

QGS405

QComboBox.activated[str] has been removed in Qt6. Use QComboBox.textActivated instead.

Why is this bad?

Qt6 api removed QComboBox.activated str overload. Only int overload remains.

Example

# Bad
combo_box.activated[str].connect(signal)

# Good
combo_box.textActivated.connect(signal)

QGS406

QRegExp has been removed in Qt6, use QRegularExpression instead.

Why is this bad?

QRegExp has been removed from Qt6 api.

Example

# Bad
from qgis.PyQt.QtCore import QRegExp

re = QRegExp('foo')

# Good
from qgis.PyQt.QtCore import QRegularExpression

re = QRegularExpression('foo')

QGS407

QDesktopWidget has been removed in Qt6. Replace with some alternative approach instead.

Why is this bad?

QDesktopWidget has been removed from Qt6 api.

QGS408

Support for compiled resources has been removed in PyQt6. Directly load icon resources by file path and load UI fields using uic.loadUiType by file path instead.

[!TIP] You can also use qgis_plugin_tools.resources.load_ui_from_file.

Why is this bad?

Support for compiled resources has been removed from PyQt6 api.

Example

# Bad
from resources_rc import dialog

# Good
from pathlib import Path
from qgis.PyQt import uic

dialog, _ = uic.loadUiType(Path("ui_file.ui"))

QGS409

Many addAction calls have been removed in Qt6. Use my_action = QAction(...), obj.addAction(my_action) instead.

Why is this bad?

Many addAction calls with multiple args have been removed from Qt6 api.

Example

# Bad
menu.addAction(foo, bar, baz, qux)

# Good
action = QAction(foo, bar, baz, qux)
menu.addAction(action)

QGS410

Use NULL instead of QVariant()

Why is this bad?

PyQgs NULL has to be used explicitly.

Example

# Bad
null_value = QVariant()
null_value = QVariant(QVariant.Null)

# Good
from qgis.core import NULL

null_value = NULL

QGS411

QDateTime(yyyy, mm, dd, hh, MM, ss, ms, ts) doesn't work anymore in Qt6, port to more reliable QDateTime(QDate, QTime, ts) form.

Why is this bad?

QDateTime api has changed in Qt6.

Example

# Bad
dt = QDateTime(2026, 1, 26, 0, 0, 0, 0, 0)

# Good
dt = QDateTime(QDate(2026, 1, 26), QTime(0, 0, 0, 0), 0)

QGS412

QGS412 QDateTime(QDate(...)) doesn't work anymore in Qt6, port to more reliable QDatetime(QDate, QTime(0,0,0)) form.

Why is this bad?

QDateTime api has changed in Qt6.

Example

# Bad
dt = QDateTime(QDate(2026, 1, 26))

# Good
dt = QDateTime(QDate(2026, 1, 26), QTime(0, 0, 0, 0))

Development

This project uses uv to manage python packages. Make sure to have it installed first.

Install development dependencies

# Activate the virtual environment
$ source .venv/bin/activate
$ uv sync
# Install pre-commit hooks
$ pre-commit install

Updating dependencies

uv lock --upgrade

Contributing

Contributions are very welcome.