Question

违规NewLevel函数中的注释提供了一些解释。

fuelstats.txt是一个文件，其中包含一个数字94.5

当我运行此代码时，错误是：

unsupported operand - for float to StringVar

这适用于new_level.set(fuel_level - kmltr)，因为其中一个是浮动的但是我已经尝试了所有我能想到的改变类型的东西，我甚至尝试过get()错误的方式，我不知道。

##call the tkinter module first with all libraries
##call the ttk module next but without all libraries so that
##I can use different lib as I need to
##...without the ttk lib I need to explicitly call the ttk function
from tkinter import *
from tkinter import ttk

##import fuel level from file
file = 'fuelstats.txt'
stats = open("fuelstats.txt").readlines()
##assign fuellevel to variable
fuel_level = stats[-1]
fuel_level = float(fuel_level)
ratekm = 2.5


###defining the calculate function here because it needs to be
###referenced early in the code
def calculate(*args):
    value = float(km.get())
    kmltr.set(value / ratekm)
    ##call the next function
    NewLevel()

def NewLevel(*args):
    global new_level
    ##this function does not work, it throws an exception
    ## that I cannot subtract a float from a stringVar
    ## this is obvious but how do I define the types properly?
    new_level.set(fuel_level - kmltr)


def km_left():
    global reserves
    reserves = fuel_level * 2.5
    n = 2
    reserves = '{:.{}f}'.format(reserves, n)

root = Tk() ##set up main window container
root.title("Calculate Fuel")## give it a title

##next set up a frame widget which holds all the content
mainframe = ttk.Frame(root, padding="30 13 20 12")
mainframe.grid(column=0, row=0, sticky=(N, W, E, S))
##these two lines tell tk to resize with main window
mainframe.columnconfigure(0, weight=1)
mainframe.rowconfigure(0, weight=1)



##define variables
km = StringVar()
kmltr = StringVar()
reserves = StringVar()
new_level = StringVar()

##call to functions
km_left()

##next create the three main widgets - input field for km
km_entry = ttk.Entry(mainframe, width=7, textvariable=km)
km_entry.grid(column=2, row=3, sticky=(W,E))

##the result fields (as labels) and the calculate button
ttk.Label(mainframe, text=fuel_level).grid(column=2, row=1, sticky=W)
ttk.Label(mainframe, text=reserves).grid(column=2, row=2, sticky=W)
ttk.Label(mainframe, textvariable=kmltr).grid(column=2, row=4, sticky=W)
ttk.Label(mainframe, text=new_level).grid(column=2, row=5, sticky=W)
ttk.Button(mainframe, text="Calculate", command=calculate).grid(column=5, row=6, sticky=W)

##below I create labels for the widgets and place them in a the grid
ttk.Label(mainframe, text="km").grid(column=3, row=2, sticky=W)
ttk.Label(mainframe, text="litres").grid(column=3, row=1, sticky=E)
ttk.Label(mainframe, text="litres").grid(column=3, row=4, sticky=E)
ttk.Label(mainframe, text="fuel level is: ").grid(column=1, row=1, sticky=W)
ttk.Label(mainframe, text="fuel reserves = ").grid(column=1, row=2, sticky=W)
ttk.Label(mainframe, text="enter km traveled ").grid(column=1, row=3, sticky=W)
ttk.Label(mainframe, text="fuel used is: ").grid(column=1, row=4, sticky=W)
ttk.Label(mainframe, text="new fuel level is: ").grid(column=1, row=5, sticky=W)

##below is a loop to put padding around each field and widget
for child in mainframe.winfo_children(): child.grid_configure(padx=5, pady=5)

km_entry.focus() ##focus of the first field
root.bind('<Return>', calculate)##and allow the enter key to act as the button

root.mainloop()
##This final line tells Tk to enter its event loop,
## which is needed to make everything run.

Answer 1

您需要获取StringVar中的值，然后将转换为float。

new_level.set(fuel_level - float(kmltr.get()))

tk代码错误，不支持的操作数

1 个答案: