Python Tkinter实战：从Hello World到多语言翻译工具

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"《用例子学习Tkinter》是David Love撰写的一本关于Python GUI编程的书籍，通过实际示例帮助读者理解并掌握Tkinter库的使用。书中详细介绍了如何使用Tkinter创建各种应用程序，包括简单的Hello World程序、待办事项列表和多语言翻译工具等。" Tkinter是Python的标准GUI（图形用户界面）库，它允许程序员创建丰富的桌面应用。这本书针对的是对Python有一定基础，想要涉足GUI编程的读者。书中强调通过实践来学习，鼓励读者在阅读过程中动手编写代码。首先，书中介绍了Tkinter的基础知识，包括安装方法、Tkinter的作用以及为何选择Tkinter作为学习目标。尽管Tkinter有时被批评为样式老旧，但其作为Python内置库，易于上手且兼容性好，是初学者入门GUI编程的理想选择。在“Hello World”部分，书中展示了如何创建一个基本的窗口应用。从最简单的单行代码实例开始，然后逐步引入面向对象编程的概念，通过定义类来组织代码，使程序更易于维护和扩展。接下来，书中通过构建一个待办事项列表应用来演示更复杂的交互功能。这个应用包含添加任务、删除任务和滚动显示等功能。通过使用Canvas和Frame元素，实现了可滚动的任务列表，并且添加了处理任务的逻辑。此外，还讨论了如何将数据持久化存储，以确保在程序关闭后还能保留任务数据。在待办事项列表的基础上，书中进一步引入了数据库集成，使用SQLite数据库来存储任务。这涵盖了数据库查询和操作的基本概念，如`runQuery`函数用于执行SQL语句，以及`firstTimeDb`用于初始化数据库。最后一部分，书中介绍了一个多语言翻译工具的实现，利用了第三方库requests进行网络请求，获取翻译服务的数据。这个工具包含了多个选项卡和菜单，使得用户可以方便地在多种语言间切换。同时，还提供了复制翻译结果到剪贴板的功能。每章末尾通常会提到下一个迭代或改进的方向，鼓励读者不断探索和优化自己的代码，以提升技能。《用例子学习Tkinter》是一本实用的指南，通过实际项目帮助读者掌握Tkinter，并逐步构建复杂的GUI应用。

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2.2. SCROLLING AND DELETING 15

2.2.1 Canvases and Frames

With this re-write, I have introduced some new components - a Canvas and two Frames. A Canvas is a

powerful general-use widget with many capabilities (usually graphical). We are using it here for its ability

to scroll, which we need if we want to add a lot of apps to our list. A Frame is a layout component which

can be used to group together multiple other widgets. As you will see in this case, we can actually use

the Canvas to draw a Frame into our window, which is then able to bundle together all of our to-do items,

allowing them to scroll independently of the Text widget we use to add new tasks.

2.2.2 __init__

As above, we now create a Canvas and two Frames, with one Frame parented to the canvas, and the other to

the main window. We then make a Scrollbar object to allow scrolling of the page. We set the orientation

and command to tell tkinter that we want a vertical scrollbar, scrolling in the y direction. We also conﬁgure

our canvas to accept the Scrollbar’s values. We once again set the window title and size, and create our

Text widget - this time parented to one of the frames (which will be packed to the bottom). Our Canvas

is packed with instruction to ﬁll all available space and expand as big as it can, and our Scrollbar follows,

ﬁlling up the vertical space.

The next line looks a little strange. We use our Canvas to create a new window inside itself, which is

our Frame holding the tasks. We create it at the coordinates (0,0) and anchor it to the top of the Canvas

(the "n" here is for "north", so top-left would require "nw", and so on). One thing to note is that we do

not pack our tasks_frame, as it will not appear, and we will be left scratching our heads as to where it is.

This is something I learned the hard way!

After that, we pack our Text into its frame and then pack its frame to the BOTTOM of the window,

with both ﬁlling the X direction. The default task is created and we bind the self.remove_task function

to it being clicked (this will be covered below). We pack this, and then move on to a big block of binds.

The <MouseWheel>, <Button-4> and <Button-5> binds handle scrolling, and the <Configure> binds handle

keeping the Canvas as big as possible as the window changes size. The <Configure> event is ﬁred when

widgets change size (and on some platorms, location) and will provide the new width and height. The

<Return> bind and colour_schemes remain from the previous example.

2.2.3 Handling Tasks

The add_task method is almost the same as the previous iteration, but the code for choosing the styling

has been moved into a separate method - set_task_colour - so that it can be re-used after deleting

tasks. Speaking of which, we have a remove_task method which will handle getting rid of the Label widget

associated with the task. To avoid accidental removal, we use an askyesno pop-up message to double-check

with the user that they wanted to delete that task (make sure you don’t miss the new import tkinter.

messagebox as msg statement at the top of the ﬁle). This will create a small notice with the title "Really

Delete?" and the message "Delete <task>?" (where <task> will be the text within the Label) with the

options "yes" and "no". Using the if statement around this means the indented code will only happen if the

user presses "yes". Upon deletion, we recolour all remaining tasks in our alternating pattern, as otherwise

the pattern would be broken by the removal.

2.2.4 Adjusting the canvas

Our on_frame_configure method is bound to our root’s <Configure> action, and will be called whenever

the window is resized. It sets the scrollable region for our canvas, and uses the bbox (bounding box) to

specify that we want the entire canvas to be scrollable. The task_width method is bound to the Canvas’s

<Configure>, and is responsible for ensuring the task Labels stay at the full width of the canvas, even after

stretching the window.

2.3. PERMANENT STORAGE 19

2.3.1 runQuery

Let’s start by explaining the database handling. Our runQuery method is a fairy generic database handling

method. It takes an sql string, some data to format into the sql string, and receive which indicates to the

method whether or not it needs to return any data (from a SELECT statement). We ﬁrst connect to our

database ﬁle, in this case tasks.db, and receive a cursor. The cursor is used to execute queries against

the database and sometimes return data. We then close oﬀ our connection at the end to reduce resource

usage. This is a static method so that it can be called by our proceeding firstTimeDb method, which needs

to be called before our __init__, and so is also static.

2.3.2 ﬁrstTimeDb

This function is used to create the database ﬁle, tasks.db, if it does not already exist. We also put our

old default task, --- Add Tasks Here ---, in this method so that it appears when the user ﬁrst loads the

app, but is permanently deletable like other tasks.

2.3.3 __init__

We start by just updating the window’s title bar to the 3rd version. We move the existing colour_schemes

variable to above the new code which will populate our existing tasks, so that we can use it during the

initial set-up. Without doing this, we would get an error when we reference it via add_task. Instead of

the hard-coded default task, we now fetch existing tasks from the database with load_tasks, then iterate

through them, passing each to our slightly altered add_task method.

2.3.4 add_task and remove_task

To prevent re-writing most of this code in our __init__ method, we have added two new parameters to

add_task: task_text and from_db. This allows us to pass in text independent of our Text widget, and

to prevent re-saving tasks to the database which originated from there. Before destroying our widget inside

remove_task, we grab its text and remove it from the database too.

2.3.5 save_task and load_tasks

These two methods deal with database access. save_task will add a new task into our database, and

load_tasks is called in our __init__ method to retrieve all saved tasks when loading the app. These two

methods ensure that the task list displays the same when the user closes then re-opens the app.

2.3.6 The ﬁnal app

That’s it for our to-do list. We now have a to-do application which can save and retrieve tasks which remain

after closing the app. We have learned how to layout multiple widgets with Frames and the pack method,

how to make a scrollable area which maintains its size when the window is resized, how to bind methods

to user inputs and tkinter’s own events, and how to dynamically add and remove widgets based on user

actions. If you read the ﬁnal section, you will also know how to integrate tkinter nicely with a sqlite

database. Next up we will create an app which utilises a tabbed interface, also known as a Notebook.

2.3.7 Further Development

If you’d like to continue work on this project as an exercise, try the following:

• Prevent duplicate tasks by using a database look-up before adding a new task.

• Give each task a "Delete" button instead of the on-click event on the Label itself (Buttons will be

covered next chapter).

• Instead of destroying tasks, mark them as "ﬁnished" using a column in the database and display them

as "greyed out".

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