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Fidget is an adapter of Qt into a functional-style interface. Fidget can be used seamlessly with PySide6, PySide2, PyQt5. Fidget is designed to create an effortless and rich UI for data science and analysis.

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Fidget is an adapter of Qt6/Qt5 into a functional-style interface. Fidget can be used seamlessly with PySide6, PySide2 and PyQt5. Fidget is designed to create an effortless and rich UI for data science and analysis.


Usage of fidget is centered around the Fidget class. Simply put, a Fidget (short for Functional Widget) is a QWidget with a value. This value can then be read and used by parent widgets, or by the python program.

Sample Usage

from typing import Tuple

from fidget.backend.QtWidgets import QLineEdit, QHBoxLayout, QApplication
from fidget.core import Fidget, ParseError

class PointWidget(Fidget[Tuple[float, float]]):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.x_edit = None
        self.y_edit = None

    def init_ui(self):

        layout = QHBoxLayout()
        with self.setup_provided(layout):
            self.x_edit = QLineEdit()

            self.y_edit = QLineEdit()

    def parse(self):
            x = float(self.x_edit.text())
        except ValueError as e:
            raise ParseError('error in x') from e

            y = float(self.y_edit.text())
        except ValueError as e:
            raise ParseError('error in y') from e

        return x, y

app = QApplication([])
w = PointWidget('point', make_indicator=True, make_plaintext=True, make_title=True)
res = app.exec_()
if res != 0:

Phew, a lot of this is standard QWidget usage, so we'll just go over the new bits:

class PointWidget(Fidget[Tuple[float, float]]):

Every Fidget must extend the Fidget class (which extend the QWidget class). Fidget is a generic type, so it can be parametrized with its value type (in this case, a tuple of floats). Like all generic types, the generic parameter has no effect on the code.

with self.setup_provided(layout):

Fidget provides some additional widgets called provided widgets, that can be added to it to improve usability. These can range from a simple title label, a label that changes to indicate whether the UI's state is valid, or even a button that opens a complex dialog with multiple methods to import/export the value as plain text. The setup_provided method returns a convenience context manager that adds these provided widgets before and after the main UI. All these provided widgets can be disabled either with constant values in the inheriting class, or with arguments when the widget is created (PointWidget('point', make_indicator=True, make_plaintext=True, make_title=True)).


The Fidget must be notified for when its value changes due to its children's value changing. So its change_value slot must be connected to any such signal.

def parse(self):

This is an abstract method that all Fidgets must implement. It processes the internal state of the widget's children, and returns a value (or raises a ParseError)


each Fidget has a value in store, that can be extracted and used as normal. Note that this value is either a fidget.core.fidget_value.GoodValue or a fidget.core.fidget_value.BadValue. These can be easily distinguished with the is_ok() method.

This is all a lot of work, fidget comes with many default implementations to make usage as effortless as possible:

from fidget.backend.QtWidgets import QHBoxLayout, QApplication
from fidget.widgets import FidgetInt, FidgetTuple

class PointWidget(FidgetTuple):
        FidgetInt.template('x', make_title=False),
        FidgetInt.template('y', make_title=False)
    MAKE_TITLE = True
    LAYOUT_CLS = QHBoxLayout

app = QApplication([])
w = PointWidget('point')
res = app.exec_()
if res != 0:

This will create a widget with similar capabilities as the one above.

Plaintext Capability

One of fidget's most extensive features is its plaintext conversion capability. Each Fidget has a set of plaintext printers and plaintext parsers, that can be selected to import/export a Fidget's value. By default, a Fidget has no plaintext parsers, and only str and repr as printers.

Adding printers and parsers

Printers and parsers can be added either by implementing the Fidget's plaintext_printers or plaintext_parsers methods, or by creating a method in the class wrapped with InnerPlaintextPrinter or InnerPlaintextParser.

Dual API

As seen in the example, almost all of the parameters the Fidget can provided upon creation can also have a default value filled in by extending classes.

from fidget.widgets import FidgetCheckBox

w = FidgetCheckBox('title', ('YES', 'NO'), make_title=True)
# the following will create a widget equivalent to w
class MyFidgetCheckBox(FidgetCheckBox):

w = MyFidgetCheckBox('title', ('YES', 'NO'))

Support Widgets

Fidget comes with many builtin widgets to ease usage. Most usages will not have subclass Fidget or implement parse at all!

Fidget subclass description
FidgetCheckBox a checkbox holding one of two values
FidgetCombo a combobox holding one of a number of values
FidgetComplex a line edit for a complex
FidgetConfirmer a fidget wrapper that includes an "OK" button to perform more complex validation
FidgetConverter a fidget wrapper that converts an inner value to an outer value
FidgetDict a fidget that aggregates multiple fidgets into a dict
FidgetEditCombo an editable combobox holding one of a number of values or a converted string value
FidgetFloat a line edit for a float
FidgetFilePath a line edit and a browse button to select a file path
FidgetInt a line edit for an int
FidgetLabel a constant-value fidget with a label
FidgetLineEdit a line edit holding any single-value string
FidgetOptional a fidget wrapper that can disable the inner fidget and provide a default value
FidgetQuestion a specialized FidgetConfirmer that opens as a dialog
FidgetStacked multiple fidgets of the same type, only one of which is usable at any time
FidgetTuple a fidget that aggregates multiple fidgets into a tuple


Fidget can use either PySide6, PySide2 or PyQt5. By default, it will try to import them in the follwing order: PySide6, PySide2 or PyQt5. It will use the first it successfully imported. This can be changed with fidget.backend's function: prefer.

Users of fidget can also directly use whatever backend fidget is using (thus ensuring compatibility) by importing Qt's members from fidget.backend (currently, only imports from QtGui, QtWidgets and QtCore are supported in this way)

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