Python文件读写

Question

我有有分数的档案：

Foo 12
Bar 44

我试着整理它，删除它，而不是写排序的分数在里面。但我错了：

ValueError:关闭文件上的I/O操作

这是我的功能：

def Sort():
scores = []
with open("results.txt") as x:
    for linia in x:
        name,score=linia.split(' ')
        score=int(score)
        scores.append((name,score))
    scores.sort(key=lambda sc: sc[1])
x.truncate()
for name, score in scores:
    x.write(name+' '+str(score))

Answer 1

该文件仅在块的中保持打开。之后，Python将自动关闭它。您需要第二次打开它，使用第二个with块。

def Sort():
    scores = []
    with open("results.txt") as x:
        # x is open only inside this block!
        for linia in x:
            name, score=linia.split(' ')
            score = int(score)
            scores.append((name, score))
        scores.sort(key=lambda sc: sc[1])

    with open("results.txt", "w") as x:
        # open it a second time, this time with `w`
        for name, score in scores:
            x.write(name + ' ' + str(score))

Sort()

这也可以通过只打开一个文件来完成。在本例中，您以双重读/写模式(r+)打开文件，并使用truncate删除以前的文件内容。

def Sort():
    scores = []
    with open("results.txt", "r+") as x:
        for linia in x:
            name, score = linia.split(' ')
            score = int(score)
            scores.append((name, score))
        scores.sort(key=lambda sc: sc[1])

        # Go to beginning of file
        x.seek(0)

        # http://devdocs.io/python~3.5/library/io#io.IOBase.truncate
        # If no position is specified to truncate, 
        # then it resizes to current position

        x.truncate()
        # note that x.truncate(0) does **not** work,
        # without an accompanying call to `seek`.
        # a number of control characters are inserted
        # for reasons unknown to me.

        for name, score in scores:
            x.write(name + ' ' + str(score) + '\n')

然而，就我个人而言，我觉得第一种方法更好，而且你不太可能射中自己的脚。