摘要：輸入框和標(biāo)簽都帶了一個(gè)神秘的參數(shù)。我們可以在之前調(diào)用的時(shí)候做這些事，但上面這樣做也是個(gè)不錯(cuò)的選擇第二行告訴讓我們的輸入框獲取到焦點(diǎn)。

原文http://www.tkdocs.com/tutorial/firstexample.html

A First (Real) Example
With that out of the way, let"s try a slightly more useful example, which will give you an initial feel for what the code behind a Tk program looks like.
我們?cè)囍鰝€(gè)稍微實(shí)用的例子，通過(guò)這種方式，讓你感受一下Tk的程序代碼是什么樣的

Design
設(shè)計(jì)
The example we"ll use is a simple GUI tool that will convert a number of feet to the equivalent number of meters. If we were to sketch this out, it might look something like this:我們將用簡(jiǎn)單的GUI工具來(lái)創(chuàng)建這個(gè)例子。他能把英尺轉(zhuǎn)換為公尺。如果我們畫了草圖，那他看起來(lái)應(yīng)該是這個(gè)樣子：

A sketch of our feet to meters conversion program.

我們的英尺轉(zhuǎn)公尺程序的草圖

So it looks like we have a short text entry widget that will let us type in the number of feet, and a "Calculate" button that will get the value out of that entry, perform the calculation, and then put the resulting number of meters on the screen just below where the entry is. We"ve also got three static labels ("feet", "is equivalent to", and "meters") which help our user figure out how to use the interface.

看起來(lái)我們需要一個(gè)文本輸入框來(lái)輸入英尺，一個(gè)“Calculate”按鈕來(lái)取得文本框的值并執(zhí)行計(jì)算，在輸入框下方輸出轉(zhuǎn)換后的值，我們同樣需要3個(gè)標(biāo)簽 ("feet", "is equivalent to", 和 "meters") 幫助用戶理解怎么用

In terms of layout, things seem to naturally divide into three columns and three rows:
布局方面，我們可以設(shè)計(jì)成3行3列的形式

The layout of our user interface, which follows a 3 x 3 grid.
我們界面的布局，一個(gè)3x3的網(wǎng)格

Code
代碼
Now here is the Python code to create thie program.
下面是這程序Python代碼（譯注：這是python3的代碼，python2中有稍許不同，下面會(huì)提到）

from tkinter import *
from tkinter import ttk
def calculate(*args):
    try:
        value = float(feet.get())
        meters.set((0.3048 * value * 10000.0 + 0.5)/10000.0)
    except ValueError:
        pass
    
root = Tk()
root.title("Feet to Meters")
mainframe = ttk.Frame(root, padding="3 3 12 12")
mainframe.grid(column=0, row=0, sticky=(N, W, E, S))
mainframe.columnconfigure(0, weight=1)
mainframe.rowconfigure(0, weight=1)
feet = StringVar()
meters = StringVar()
feet_entry = ttk.Entry(mainframe, width=7, textvariable=feet)
feet_entry.grid(column=2, row=1, sticky=(W, E))
ttk.Label(mainframe, textvariable=meters).grid(column=2, row=2, sticky=(W, E))
ttk.Button(mainframe, text="Calculate", command=calculate).grid(column=3, row=3, sticky=W)
ttk.Label(mainframe, text="feet").grid(column=3, row=1, sticky=W)
ttk.Label(mainframe, text="is equivalent to").grid(column=1, row=2, sticky=E)
ttk.Label(mainframe, text="meters").grid(column=3, row=2, sticky=W)
for child in mainframe.winfo_children():child.grid_configure(padx=5, pady=5)
feet_entry.focus()
root.bind("", calculate)
root.mainloop()

And the resulting user interface:

Screenshot of our completed feet to meters user interface (on Mac OS X, Windows and Linux).
程序運(yùn)行的截圖

Step-by-Step Walkthrough
分步演練
Let"s take a closer look at that code, piece by piece. For now, all we"re trying to do is get a basic understanding of the types of things we need to do to create a user interface in Tk, and roughly what those things look like. We"ll go into details later.
讓我們看看這些代碼，一點(diǎn)點(diǎn)來(lái)，現(xiàn)在我們要做的事情是，對(duì)我們要?jiǎng)?chuàng)建一個(gè)Tk界面有一個(gè)基本理解并知道他大概是什么樣的，稍后我們來(lái)講講細(xì)節(jié).

Python3代碼：

from tkinter import *
from tkinter import ttk

Python2代碼：

from Tkinter import *
import ttk #python2中ttk是獨(dú)立的模塊

These two lines tell Python that our program needs two modules. The first,?"tkinter", is the standard binding to Tk, which when loaded also causes the existing Tk library on your system to be loaded. The second,?"ttk", is Python"s binding to the newer "themed widgets" that were added to Tk in 8.5.
這兩行代碼告訴Python我們的程序需要兩個(gè)模塊，第一個(gè)是tkinter，這個(gè)Tk所必須的，導(dǎo)入這個(gè)模塊時(shí)你系統(tǒng)中的Tk相關(guān)庫(kù)也會(huì)同時(shí)被加載。第二個(gè)是ttk，這是Tk 8.5版本后新增的主題控件（譯注：關(guān)于python中Tk的版本?？梢栽趯?dǎo)入tkinter模塊后執(zhí)行tkinter.Tcl().eval("info patchlevel")或者Tkinter.Tcl().eval("info patchlevel")查看版本，前者是python2，后者是pyhton3。Tk在從python2遷移到python3時(shí)把名字從Tkinter改成了tkinter）

tips：
提示：
Notice that we"ve imported everything from the tkinter module, so that we can call tkinter functions etc. without prefixing them, which is standard Tkinter practice. However, because we"ve imported just "ttk" itself, that means we"ll need to prefix anything inside that module. So for example calling "Entry(...)" would invoke the function inside the tkinter module, while we"d need "ttk.Entry(...)" to invoke the function inside ttk. As you"ll see, several functions are defined in both modules, and sometimes you will need both, depending on the context. Making the ttk calls explicit facilitates this, and will be the style used in this tutorial.
注意，我們導(dǎo)入了tkinter所有的模塊，所以我們可以直接使用tkinter的所有功能，這是Tkinter的標(biāo)準(zhǔn)做法，然而，我們?cè)诤竺鎸?dǎo)入了ttk，這意味著我們接下來(lái)要用到的組件前面都得加前綴，舉個(gè)例子，直接調(diào)用“Entry”會(huì)調(diào)用tkinter內(nèi)部的模塊，然而我們需要的是ttk里的“Entry”，所以要用“ttk.Enter”，如你所見(jiàn)，許多函數(shù)在兩者之中都有，如果同時(shí)用到這兩個(gè)模塊，你需要根據(jù)整體代碼選擇用哪個(gè)模塊，讓ttk的調(diào)用更加清晰，本教程中也會(huì)使用這種風(fēng)格

root = Tk()
root.title("Feet to Meters")
mainframe = ttk.Frame(root, padding="3 3 12 12")
mainframe.grid(column=0, row=0, sticky=(N, W, E, S))
mainframe.columnconfigure(0, weight=1)
mainframe.rowconfigure(0, weight=1)    

FYI:Yes, the?"calculate"?function appeared before this. We"ll describe it down below, but need to include it near the start because we reference it in other parts of the program.
僅供參考：沒(méi)錯(cuò) ，“calculate"方法在這之前定義了，我們稍后在討論他，但需要先在開始的地方定義好，因?yàn)橹笪覀儠?huì)在其他地方調(diào)用到它

Next, the above lines set up the main window, giving it the title "Feet to Meters". Next, we create a frame widget, which will hold all the content of our user interface, and place that in our main window. The?"columnconfigure"/"rowconfigure"?bits just tell Tk that if the main window is resized, the frame should expand to take up the extra space.
接下來(lái)，上面的那些代碼創(chuàng)建了主窗口，設(shè)置窗口的標(biāo)題為“Feet to Meters”，然后，我們創(chuàng)建了一個(gè)frame控件，用戶界面上的所有東西都包含在里面，并且放在主窗口中。columnconfigure"/"rowconfigure是告訴Tk如果主窗口的大小被調(diào)整，frame空間的大小也隨之調(diào)整

feet = StringVar()
meters = StringVar()
feet_entry = ttk.Entry(mainframe, width=7, textvariable=feet)
feet_entry.grid(column=2, row=1, sticky=(W, E))
ttk.Label(mainframe, textvariable=meters).grid(column=2, row=2, sticky=(W, E))
ttk.Button(mainframe, text="Calculate", command=calculate).grid(column=3, row=3, sticky=W)

FYI：
Strictly speaking, we could just put the other parts of our interface directly into the main root window, without the intervening content frame. However, the main window isn"t itself part of the "themed" widgets, so its background color wouldn"t match the themed widgets we will put inside it. Using a "themed" frame widget to hold the content ensures that the background is correct.
僅供參考：嚴(yán)格來(lái)講，我們要做的僅僅是把其他控件直接塞進(jìn)主窗口中就行，不需要使用frame空間。然而，主窗口自身并不是“帶主題”的控件的一部分，所以如果我們把“帶主題”的控件放入主窗口，他的背景顏色不能和“帶主題”的控件相匹配。用一個(gè)frame控件可以使得“帶主題”的控件和主窗口的背景相匹配

The preceding lines create the three main widgets in our program: the entry where we type the number of feet in, a label where we put the resulting number of meters, and the calculate button that we press to perform the calculation.

上面的那幾行代碼為我們的程序創(chuàng)建了3個(gè)主要的控件：用來(lái)輸入英尺的輸入框，一個(gè)用來(lái)輸出轉(zhuǎn)換成米單位結(jié)果的標(biāo)簽，和一個(gè)執(zhí)行計(jì)算的計(jì)算按鈕

For each of the three widgets, we need to do two things: create the widget itself, and then place it onscreen. All three widgets, which are "children" of our content window are created as instances of one of Tk"s themed widget classes. At the same time as we create them, we give them certain options, such as how wide the entry is, the text to put inside the Button, etc. The entry and label each are assigned a mysterious?"textvariable"; we"ll see what that does shortly.

關(guān)于這三個(gè)控件，我們要做的就兩件事：創(chuàng)建，顯示。這三個(gè)控件都是窗口的“孩子”，“帶主題”控件的類的實(shí)例。同時(shí)我們?yōu)樗麄冊(cè)O(shè)置一些選項(xiàng)，比如輸入的寬度，按鈕顯示的文本等等。輸入框和標(biāo)簽都帶了一個(gè)神秘的參數(shù)“textvariable”。我們不久后還會(huì)再看到他

If the widgets are just created, they won"t automatically show up on screen, because Tk doesn"t know how you want them to be placed relative to other widgets. That"s what the?"grid"?part does. Remembering the layout grid for our application, we place each widget in the appropriate column (1, 2 or 3), and row (also 1, 2 or 3). The?"sticky"?option says how the widget would line up within the grid cell, using compass directions. So?"w"?(west) means anchor the widget to the left side of the cell,?"we"(west-east) means anchor it to both the left and right sides, and so on.
如果控件僅僅被創(chuàng)建了，他們是不會(huì)自動(dòng)顯示在屏幕上的，因?yàn)門k并不知道這些控件和其他控件的位置關(guān)系。那是“grid”那個(gè)部分要做的事情。還記得我們程序的網(wǎng)格布局么？我們把每個(gè)控件放到對(duì)應(yīng)行或者列中，”sticky“選項(xiàng)指明控件在網(wǎng)格單元中的排列，用的是指南針?lè)较颉Ｋ浴皐”代表固定這個(gè)控件在左邊的網(wǎng)格中。
“we”代表固定這個(gè)空間在左右之間。等等

ttk.Label(mainframe, text="feet").grid(column=3, row=1, sticky=W)
ttk.Label(mainframe, text="is equivalent to").grid(column=1, row=2, sticky=E)
ttk.Label(mainframe, text="meters").grid(column=3, row=2, sticky=W)

The above three lines do exactly the same thing for the three static text labels in our user interface; create each one, and place it onscreen in the appropriate cell in the grid.
上面這三行明確的為三個(gè)靜態(tài)標(biāo)簽做了一點(diǎn)小工作：創(chuàng)建，然后放在適合的網(wǎng)格位置中

for child in mainframe.winfo_children(): child.grid_configure(padx=5, pady=5)
feet_entry.focus()
root.bind("", calculate)

The preceding three lines help put some nice finishing touches on our user interface.
這三行在界面上做了一些漂亮的收尾工作

The first line walks through all of the widgets that are children of our content frame, and adds a little bit of padding around each, so they aren"t so scrunched together. We could have added these options to each?"grid"?call when we first put the widgets onscreen, but this is a nice shortcut.
第一行處理了frame中的所有控件，并且為每個(gè)空間四周添加了一些空隙，不會(huì)顯得揉成一團(tuán)。我們可以在之前調(diào)用grid的時(shí)候做這些事，但上面這樣做也是個(gè)不錯(cuò)的選擇

The second line tells Tk to put the focus on our entry widget. That way the cursor will start in that field, so the user doesn"t have to click in it before starting to type.
第二行告訴Tk讓我們的輸入框獲取到焦點(diǎn)。這方法可以讓光標(biāo)一開始就在輸入框的位置，用戶就可以不用再去點(diǎn)擊了

The third line tells Tk that if the user presses the Return key (Enter on Windows) anywhere within the root window, that it should call our calculate routine, the same as if the user pressed the Calculate button.
第三行告訴Tk如果用戶在窗口中按下了回車鍵，就執(zhí)行計(jì)算，等同于用戶按下了計(jì)算按鈕

def calculate(*args):
try:
    value = float(feet.get())
    meters.set((0.3048 * value * 10000.0 + 0.5)/10000.0)
except ValueError:
    pass

Here we define our calculate procedure, which is called either when the user presses the Calculate button, or hits the Return key. It performs the feet to meters calculation, taking the number of feet from our entry widget, and placing the result in our label widget.
這里我們定義了計(jì)算過(guò)程，無(wú)論是按回車還是點(diǎn)計(jì)算按鈕，他都會(huì)從輸入框中取得把英尺，轉(zhuǎn)換成米，然后輸出到標(biāo)簽中

Say what? It doesn"t look like we"re doing anything with those widgets! Here"s where the magic"textvariable"?options we specified when creating the widgets come into play. We specified the global variable "feet" as the textvariable for the entry, which means that anytime the entry changes, Tk will automatically?update the global variable feet. Similarly, if we explicitly change the value of a textvariable associated with a widget (as we"re doing for "meters" which is attached to our label), the widget will automatically be updated with the current contents of the variable. Slick.
怎么樣，他看起來(lái)和前面那些控件完全不一樣，之前定義的那個(gè)魔術(shù)般的“textvariable”選項(xiàng)，在這里開始發(fā)揮作用，我們指定了全局變量“feet”成為一個(gè)textvariable來(lái)接受輸入的內(nèi)容，這意味著任何時(shí)候輸入的值被改變，Tk都會(huì)自動(dòng)的改變“feet”這個(gè)全局變量的值，同樣的，如果我們明確改變了一個(gè)textvariable相關(guān)聯(lián)的的控件的值（類似我們改變meters變量就改變了標(biāo)簽一樣），控件會(huì)自動(dòng)更新相應(yīng)的變量。

root.mainloop()

This final line tells Tk to enter its event loop, which is needed to make everything run.
最后一行是告訴Tk進(jìn)入事件循環(huán)，這是讓程序能運(yùn)行所必須的