Question

我正在尝试从包含城市名称，里程表读数以及剩余燃料量的文件中读取。文本文件的内容是：

Kennewick 97840.4 40.0<br>
Benton_City 97861.3 37.6<br>
Prosser 97878.2 35.9<br>
Grandview 97886.5 35.0<br>
Sunnyside 97894.6 34.1<br>
Granger 97904.6 33.1<br>
Toppenish 97913.0 32.2<br>
Wapato 97921.7 31.3<br>
Union_Gap 97931.6 30.4<br>
Yakima 97935.2 30.0<br>
Selah 97939.4 29.6<br>
Ellensburg 97972.7 26.0<br>
Thorp 97981.1 25.1<br>
Rosyln 98002.8 22.6<br>
Easton 98016.1 21.1<br>
North_Bend 98058.1 16.9<br>
Preston 98067.7 16.0<br>
Issaquah 98073.6 15.4<br>
East_Gate 98082.9 14.4<br>
Mercer_Island 98088.5 13.7<br>
Seattle 98095.4 13.0<br>

部分分配是从上一次读取中减去当前的读取（存储在变量里程中的两个值）。

def BusRoute():
    path = "C:\\"
    ext = ".txt"

    lines = ""
    stopname = ""
    miles = 0
    prevmiles = 0
    milest = 0
    fuel = 0.0
    mpg = 0.0
    i = 0

    filename = input("Please enter the file name. The file path [C:\...] and extension [*.txt] is not required: ")

    inFile = open(path + filename + ext, "r")

    for lines in inFile:
        stopname, miles, fuel = lines.split(" ")

        miles = float(miles)
        fuel = float(fuel)

        prevmiles = miles

        milest = miles - prevmiles

        miles += 1

        print("Since last stop:", float(milest), "miles")

我的问题是，我正在尝试将miles的最后读取值存储在名为prevmiles的变量中，然后从CURRENT中减去prevmiles（最后读取的里程数）读取miles，但它会从当前miles中减去当前miles，显然会使我想要的值打印出0.0。

Answer 1

你有

prevmiles = miles

milest = miles - prevmiles

保证里程数为0.尝试只切换这两行的顺序。

Answer 2

这里有两件事：

您需要使用文件的第一行初始化stopname，prevmiles和fuel，
您需要交换将miles分配给prevmiles的两行。

这是更新后的功能：

def BusRoute():
    path = "C:\\"
    ext = ".txt"

    lines = ""
    stopname = ""
    miles = 0
    prevmiles = 0
    milest = 0
    fuel = 0.0
    mpg = 0.0
    i = 0

    filename = input("Please enter the file name (no extension)").strip()

    inFile = open(path + filename + ext, "r")

    stopname, prevmiles, fuel = inFile.readline().split()
    prevmiles = float(prevmiles)
    fuel = float(fuel)

    for lines in inFile:
        stopname, miles, fuel = lines.split(" ")

        miles = float(miles)
        fuel = float(fuel)

        milest = miles - prevmiles

        prevmiles = miles

        miles += 1

        print("Since last stop:", float(milest), "miles")

Answer 3

您应该只更改操作的顺序。首先进行减法，然后为前一个值赋值。

Answer 4

我切换了两条线，得到了我认为你正在寻找的东西。

prevmiles = miles

milest = miles - prevmiles

注意 - 此代码适用于Python 2.5.4，因此语法会在几个部分中发生变化，并且由于行末的第一部分，因为燃料的浮点数会产生错误，所以我对此进行了评论。

def BusRoute():
    path = "C:\\"
    ext = ".txt"

    lines = ""
    stopname = ""
    miles = 0
    prevmiles = 0
    milest = 0
    fuel = 0.0
    mpg = 0.0
    i = 0

    filename = raw_input("Please enter the file name. The file path [C:\...] and extension [*.txt] is not required: ") #raw_input for text in Python 2.5

    inFile = open(path + filename + ext, "r")

    for lines in inFile:
        stopname, miles, fuel = lines.split(" ")

        miles = float(miles)
        ##fuel = float(fuel) (Gives me an error message)

        milest = miles - prevmiles

        prevmiles = miles            

        miles += 1

        print "Since last stop:", float(milest), "miles" #Print syntax is different in Python 2.5

BusRoute()

给出输出：

Please enter the file name. The file path [C:\...] and extension [*.txt] is not required: name
Since last stop: 97840.4 miles
Since last stop: 20.9 miles
Since last stop: 16.9 miles
Since last stop: 8.3 miles
Since last stop: 8.10000000001 miles
Since last stop: 10.0 miles
Since last stop: 8.39999999999 miles
Since last stop: 8.7 miles
Since last stop: 9.90000000001 miles
Since last stop: 3.59999999999 miles
Since last stop: 4.2 miles
Since last stop: 33.3 miles
Since last stop: 8.40000000001 miles
Since last stop: 21.7 miles
Since last stop: 13.3 miles
Since last stop: 42.0 miles
Since last stop: 9.59999999999 miles
Since last stop: 5.90000000001 miles
Since last stop: 9.29999999999 miles
Since last stop: 5.60000000001 miles
Since last stop: 6.89999999999 miles

为什么不尝试在循环中打印文件里程以确保获得正确的值？

从文件中读取，存储值和数学运算

4 个答案: