def callback():
    var.set("hhhhhhh")

root = Tk()

var = StringVar()
var.set("66666")


frame1 = Frame(root)
frame2 = Frame(root)


lb = Label(frame1,textvariable=var,padx=20)
lb.pack(side=LEFT)

# img = Image(file="1.gif",imgtype="photo")
img = PhotoImage(file="1.gif")
lb2 = Label(frame1,image=img)
lb2.pack(side=RIGHT)

btnCm = Button(frame2,text="下一步",command=callback)
btnCm.pack()

frame1.pack()
frame2.pack()

root.mainloop()

from tkinter import *

root =Tk()

v = IntVar()    #选中为1，未选中为0

c = Checkbutton(root,text="Test",variable=v)
c.pack()

l = Label(root,textvariable=v)
l.pack()

root.mainloop()

from tkinter import *

root =Tk()

GIRLS = ["asd",‘dsa‘,‘fef‘,‘fwaf‘]

v = []

def change():
    for i in v:
        print(i.get())

for girl in GIRLS:
    v.append(IntVar())
    b = Checkbutton(root,text=girl,variable=v[-1],command=change)  #使用一个固有变量来记录状态
    b.pack(anchor=W)    #控件相对主窗口在左边


root.mainloop()

#对于单选框，多个按钮只对应一个变量，复选框，多个按钮对应多个值
from tkinter import *

def change():
    print(v.get())

root = Tk()

v = IntVar()

Radiobutton(root,text="one",variable=v,value=1,command=change).pack(anchor=W)
Radiobutton(root,text="two",variable=v,value=2,command=change).pack(anchor=W)
Radiobutton(root,text="three",variable=v,value=3,command=change).pack(anchor=W)

root.mainloop()

from tkinter import *

def change():
    print(v.get())


root = Tk()
v = IntVar()

Langes = [
    ("python",1),
    ("javascript",2),
    ("Lua",3),
    ("Ruby",4)
]

for key,val in Langes:
    Radiobutton(root,text=key,variable=v,value=val,command=change).pack(anchor=W)

root.mainloop()

1.首先进入IntVar类
class IntVar(Variable):
    def __init__(self, master=None, value=None, name=None):
        Variable.__init__(self, master, value, name)
2.进入父类
class Variable:
    def __init__(self, master=None, value=None, name=None):
        ...
        if not master:    #看此处（master是主窗口，是传参，但是我们使用的时候并没有传入，所以为空，进入下面代码）
            master = _default_root    #_default_root是什么
        self._root = master._root()
        self._tk = master.tk
        ...
3._default_root查找
_support_default_root = 1    #也有用，后面看
_default_root = None #是一个全局变量，代表主窗口
但是他也为空，所以出现了上面的属性错误，None没有_root()方法
------------------------------------------------------------------

开始查看Tk()
root = Tk()
1.查看源码
class Tk(Misc, Wm):
    def __init__(self, screenName=None, baseName=None, className=‘Tk‘,
                 useTk=1, sync=0, use=None):
        ...
        if useTk:    #这里默认传入1，进入下面逻辑
            self._loadtk()
       ...
2.查看self._loadtk()方法

    def _loadtk(self):
        self._tkloaded = 1
        global _default_root
        # Version sanity checks
        ......
        # Create and register the tkerror and exit commands
        # We need to inline parts of _register here, _ register
        # would register differently-named commands.
        ......
        if _support_default_root and not _default_root:    #查看上面的全局变量，发现可以进入下面的逻辑代码中
            _default_root = self    #所以_default_root就是主窗口
        ......
------------------------------------------------------------------

结论：由上面发现可以知道：
IntVar等变量的使用需要_default_root（当我们没有传入master时），而主窗口生成root=Tk()时，内部代码将_default_root实现了。所以两者顺序需要保证先后