[Tips]How to Execute Function When Tab Opens in QTreeWidget

GOAL

Today’s goal is to implement PySide Widget where a function is executed when the tab is expanded. For example, the following is a function to print opened item name.

Environment

Windows 10
Python 3.8.7
PySide2 (5.15.2)

Method

Use itemExpanded

Connect target function to itemExpanded signal of QTreeWidget.

How To Use QInputDialog in PySide

GOAL

Today’s goal is to create a simple dialog by using QInputDialog in PySide.

Environment

Windows 10
Python 3.8.7
PySide2 (5.15.2)

Method

Reference: QInputDialog

Create the simplest dialog

There are 4 types of dialogs, getText, getInt, getDouble and getItem. Here is an example of QInputDialog() in https://gist.github.com/s-nako/1821d3c25997ec4a868f1e5f0bd2f687.

getText Dialog

def show_get_text_dialog(self):
    name, ok = QInputDialog.getText(self, 'Name form', 'input name:')
    if ok:
        print("input is ", name)

Command-line Arguments and argparse in Python

GOAL

Today’s goal is to understand how to get command-line arguments in Python and how to use argparse module.

Environment

Windows 10
Python 3.8.7

What is command-line arguments in Python?

This is an example for parsing command-line arguments without argparse. The system can get the list of command line arguments with sys.argv.

import sys

def args_test():
    args = sys.argv
    for idx, args in enumerate(args):
        print(idx, args)

args_test()

An example of input in command prompt and the result are as below. Please note that the arguments are only string type and separated by spaces.

> python\test\argparse_test.py aa 100 "cc" [item1, items]

0 python\test\argparse_test.py
1 aa
2 100
3 cc
4 [item1,
5 items]

Optional arguments and flags

The following is an example to use optional arguments in command-line. It takes an effort to parse the list sys.argv.

import sys

def print_student_info():
    # the argument template name, age, --classes class1 class2 --absence
    # example1 Sulley 12 --classes math music science
    # example2 Mike 11 --absence --classes math
    args = sys.argv
    print("{} is {} years old".format(args[1], args[2]))

    if "--absence" in args:
        print("He/She is absent today.")

    if "--classes" in args:
        classes = []
        class_start = args.index("--classes")+1
        flag_item = list(filter(lambda x: x.startswith("--"), args[class_start:]))
        if flag_item:
            class_end = args.index(flag_item[0])
            classes = args[class_start:class_end]
        else:
            classes = args[class_start:]
        print("He/She has {} classes".format(" ".join(classes)))

print_student_info()

>python\test\argparse_test.py Sulley 12 --classes math music science
Sulley is 12 years old
class_start 4
He/She has math music science classes

>python\test\argparse_test.py Mike 11 --absence --classes math
Mike is 11 years old
He/She is absent today.
He/She has math classes

What is argparse?

The argparse is the module that makes it easy to write user-friendly command-line interfaces. It is useful when you’d like to use optional command-line arguments in your python program.

How to use argparse

You can add the argument with add_argument() function. Check the Python documentation for details about parameters for add_argument() such as “nargs” or “action”.

import sys
import argparse

def print_student_info():
    parser = argparse.ArgumentParser()
    parser.add_argument("name", type=str)
    parser.add_argument("age", type=int)
    parser.add_argument("--classes", nargs='*') # for list of optional arguments
    parser.add_argument("--absence", action="store_true") # for optional arguments with no value

    args = parser.parse_args()

    print("{} is {} years old".format(args.name, args.age))
    if args.absence:
        print("He/She is absent today.")
    if args.classes:
        print("He/She has {} classes".format(" ".join(args.classes)))

print_student_info()

>python\test\argparse_test.py Mike 11 --classes math science --absence
Mike is 11 years old
He/She is absent today.
He/She has math science classes

How To Add Context Menu Into QTreeWidget

GOAL

Today’s goal is to add context menu to the QTreeWidget in PySide.

Environment

Windows 10
Python 3.8.7
PySide2 (5.15.2)

Method

Change the ContextMenuPolicy of the widget.

Use CustomContextMenu if you’d like to connect your function to the signal that is emitted when the context menu is requested by actions such as right-clicked. See Qt::ContextMenuPolicy in Qt Documentation for details about ContextMenuPolocy types.

self.tree_widget = QTreeWidget()
self.tree_widget.setContextMenuPolicy(Qt.CustomContextMenu)
self.tree_widget.customContextMenuRequested.connect(self._show_context_menu)

And define the function to connect. Please use exec_() instead of show() to display the menu. The mapToGlobal function is used to determines the position to display the menu.

    # the function to display context menu
    def _show_context_menu(self, position):
        display_action1 = QAction("Display Selection")
        display_action1.triggered.connect(self.display_selection)

        menu = QMenu(self.tree_widget)
        menu.addAction(display_action1)
        
        menu.exec_(self.tree_widget.mapToGlobal(position))

Complete Code

cotext_menu_test.py

import sys
from PySide2.QtWidgets import *
from PySide2.QtCore import Qt

class MyMainWindow(QMainWindow):
    def __init__(self, parent=None):
        super(MyMainWindow, self).__init__(parent)
        self._generate_ui()
        self._init_tree_widget()

    def _generate_ui(self):
        main_widget = QWidget()
        main_layout = QVBoxLayout()
        main_widget.setLayout(main_layout)
        self.setCentralWidget(main_widget)
        self.tree_widget = QTreeWidget()
        self.tree_widget.setSelectionMode(QAbstractItemView.ExtendedSelection)

        #----------add context menu--------------------------------------
        self.tree_widget.setContextMenuPolicy(Qt.CustomContextMenu)
        self.tree_widget.customContextMenuRequested.connect(self._show_context_menu)
        #----------------------------------------------------------------

        main_layout.addWidget(self.tree_widget)

    def _init_tree_widget(self):
        headers = ["header1", "header2"]
        self.tree_widget.setHeaderLabels(headers)
        tree_widget_item1 = QTreeWidgetItem(["group1"])
        tree_widget_item1.addChild(QTreeWidgetItem(["item1_1", "item1_2"]))
        self.tree_widget.addTopLevelItem(tree_widget_item1)
        tree_widget_item2 = QTreeWidgetItem(["group2"])
        self.tree_widget.addTopLevelItem(tree_widget_item2)
        tree_widget_item2.addChild(QTreeWidgetItem(["item2_1", "item2_2"]))
        tree_widget_item2.addChild(QTreeWidgetItem(["item3_1", "item3_2"]))

    # the function to display context menu
    def _show_context_menu(self, position):
        display_action1 = QAction("Display Selection")
        display_action1.triggered.connect(self.display_selection)

        menu = QMenu(self.tree_widget)
        menu.addAction(display_action1)
        menu.exec_(self.tree_widget.mapToGlobal(position))

    # the action executed when menu is clicked
    def display_selection(self):
        column = self.tree_widget.currentColumn()
        text = self.tree_widget.currentItem().text(column)
        print("right-clicked item is " + text)

def launch():
    app = QApplication.instance()
    if not app:
        app = QApplication(sys.argv)
    widget = MyMainWindow()
    widget.show()
    app.exec_()


launch()

Result

When the item “item1_2” is right-clicked, the menu appears.

Click the “Display Selection”, the message is displayed.

How Get Value With Format in Python

GOAL

Today’s goal is to check if the string follows the format and to get the value according to the format. The following is an example.

# the format is "My name is <NAME>, the phone number is <NUMBER>" (<NUMBER> is separated by 2 '-')

str1 = "My name is Nako, the phone number is 123-456-7890"
#str1 follows the format, <NAME> is "Nako" and <NUMBER> is "1234567890" in this case

str2 = "I am Nako, the phone number is 1234567890"
# str2 doesn't follow the format

Environment

Python 3.8.7

Method

Use regular expression

Create regular expression object with re.compile(pattern, flags=0). It can be used to check if the string matches the pattern or not by using Pattern.match(string) function.

# coding: utf-8
import re

str1 = "My name is Nako, the phone number is 123-456-7890"
str2 = "I am Nako, the phone number is 1234567890"

prog = re.compile("My name is [A-Za-z]+, the phone number is [0-9]+-[0-9]+-[0-9]+$")

print(prog.match(str1))
# output => <re.Match object; span=(0, 49), match='My name is Nako, the phone number is 123-456-7890>
print(prog.match(str2))
# output => None

You can get the value by grouping the regular expression using (). The value of each group can be get with Match.group([group1, …])

gourp(0) is the entire match and group(n) is the match for n-th group.

# coding: utf-8
import re

str1 = "My name is Nako, the phone number is 123-456-7890"

prog = re.compile("My name is ([A-Za-z]+), the phone number is ([0-9]+-[0-9]+-[0-9]+)$")

match = prog.match(str1)
if match:
    print(match.group(0)) # output => My name is Nako, the phone number is 123-456-7890
    print(match.group(1)) # output => Nako
    print(match.group(2)) # output => 123-456-7890
    print(match.group(2).replace('-', '')) # output => 1234567890

Postscript

$ as the end of the string

You should use $ that matches the end of the string because Pattern.match(string) finds zero or more characters at the beginning of string match.

fullmatch method

If you don’t use $, you should use Pattern.fullmatch(string) instead of Pattern.match(string).

str1 = "My name is Nako, the phone number is 123-456-7890ABCDE"
prog = re.compile("My name is ([A-Za-z]+), the phone number is ([0-9]+-[0-9]+-[0-9]+)")

print(prog.match(str1))
# output => <re.Match object; span=(0, 49), match='My name is Nako, the phone number is 123-456-7890>

print(prog.fullmatch(str1))
# output => None

pattern with length limitation

The length of the input can be limited by {} in regular expression.

str1 = "My name is Nako, the phone number is 123-456-78900000"
prog = re.compile("My name is ([A-Za-z]+), the phone number is ([0-9]{3}-[0-9]{3}-[0-9]{4})$")

print(prog.match(str1))
# output => None