Question

该程序的基础是向用户询问.txt文件并计算文件中的行数。然后程序显示文件中的行数，用户将输入一个数字以显示文件中的特定行。如果用户点击0，程序将结束。

程序运行正常，直到我在.txt文件中输入除1或最后一个行号之外的数字。程序将反复显示“输入行号，是否要退出？点击0”。

inName = input("Enter the a valid file name: ")
inputFile = open(inName, "r")
count = 0
for line in inputFile:
    count = count + 1
print("The file has " + str(count) + " lines.")
inputFile.close()

while True:
    try:
        n = int(input("Enter a line number, want to quit? Hit 0: "))
        lineno = 0
        break
    except ValueError:
        print("Try again. Line number must be between 1 and " + str(count))

while n != 0:
    if n >= 0 and n <= count:
        inputFile = open(inName, "r")
        for line in inputFile:
            lineno = lineno + 1
            if lineno == n:
                print(line)
                inputFile.close()
            else:
                print("Try again. Line number must be between 1 and " + str(count))

            while True:
                try:
                    n = int(input("Enter a line number, hit 0 to quit: "))
                    lineno = 0
                    break
                except ValueError:
                    print("Try again. Line number must be between 1 and " + str(count))

Answer 1

我不会处理您的代码中的许多问题，因为注释和答案在那里已经做得很彻底。相反，我想通过一遍又一遍地打开和关闭文件来讨论您正在创建的I / O问题。这样做很昂贵。对于几乎所有时间都在等待用户输入的程序而言，它可能不会引起注意，但是在不需要时打开和关闭文件是一个坏习惯。

我建议采用两种解决方案之一来解决此问题。如果您正在处理小的文本文件，只需将整个内容加载到内存中，例如与file.readlines()：

inName = input("Enter the a valid file name: ")
with open(inName, "r") as file:
    data = file.readlines()
count = len(data)
print(f"The file has {count} lines.")

while True:
    try:
        n = int(input("Enter a line number, want to quit? Hit 0: "))
    except ValueError:
        print(f"Try again. Line number must be between 1 and {count}")
    else:
        if n == 0:
            break
        print(data[n - 1])

对于大文件，我同意您一次仅加载一行的技术，但是您必须对此保持精明。我将打开文件一次，创建到行首的偏移量表，然后使用该表在文件中移动：

inName = input("Enter the a valid file name: ")
with open(inName, "r") as file:
    table = [0]
    table.extend(file.tell() for _ in file)
    count = len(table) - 1  # last entry is size of file
    print(f"The file has {count} lines.")

    while True:
        try:
            n = int(input("Enter a line number, want to quit? Hit 0: "))
        except ValueError:
            print(f"Try again. Line number must be between 1 and {count}")
        else:
            if n == 0:
                break
            file.seek(table[n - 1])
            print(file.readline()

Answer 2

重构您的代码并在循环中进行一些更改，删除了您在中循环中关闭文件的部分，并将其替换为break。

如果可以尝试，请尝试：

inName = input("Enter the a valid file name: ")
inputFile = open(inName,"r")
count = 0
for line in inputFile:
    count = count + 1

print("The file has "+str(count)+" lines.");
inputFile.close()

while True:
    try:
        n = int(input("Enter a line number, want to quit? Hit 0: "))
        lineno = 0

    except ValueError:
        print("Try again. Line number must be between 1 and "+str(count))

    if n != 0:
        if n >= 0 and n <= count:
            inputFile = open(inName, "r")
            for line in inputFile:

                if lineno == n:
                    print(line)
                    #inputFile.close()
                    break
                else:
                    lineno = lineno + 1
        else:
            print("Try again. Line number must be between 1 and "+str(count))


    else:
        break

Python调试，程序不会在用户输入1之外显示文本行

2 个答案: