如何在 Python 中对文件类型进行子类化？

发布于 2024-07-26 15:13:14 字数 1609 浏览 1 评论 0原文

我正在尝试对 Python 中的内置 file 类进行子类化，以向 stdin 和 stdout 添加一些额外的功能。这是我到目前为止的代码：

class TeeWithTimestamp(file):
    """
    Class used to tee the output of a stream (such as stdout or stderr) into
    another stream, and to add a timestamp to each message printed.
    """

    def __init__(self, file1, file2):
        """Initializes the TeeWithTimestamp"""
        self.file1 = file1
        self.file2 = file2
        self.at_start_of_line = True

    def write(self, text):
        """Writes text to both files, prefixed with a timestamp"""

        if len(text):
            # Add timestamp if at the start of a line; also add [STDERR]
            # for stderr
            if self.at_start_of_line:
                now = datetime.datetime.now()
                prefix = now.strftime('[%H:%M:%S] ')
                if self.file1 == sys.__stderr__:
                    prefix += '[STDERR] '
                text = prefix + text

            self.file1.write(text)
            self.file2.write(text)

            self.at_start_of_line = (text[-1] == '\n')

目的是在每条消息的开头添加时间戳，并将所有内容记录到日志文件中。但是，我遇到的问题是，如果我这样做：

# log_file has already been opened
sys.stdout = TeeWithTimestamp(sys.stdout, log_file)

那么当我尝试执行 print 'foo' 时，我会得到一个 ValueError: I/O 操作已关闭的文件。我无法在 __init__() 中有意义地调用 file.__init__() ，因为我不想打开新文件，并且无法分配 < code>self.close = False 两者之一，因为它是只读属性。

我如何修改它，以便我可以执行 print 'foo' 操作，并使其支持所有标准 file 属性和方法？

原文

I'm trying to subclass the built-in file class in Python to add some extra features to stdin and stdout. Here's the code I have so far:

class TeeWithTimestamp(file):
    """
    Class used to tee the output of a stream (such as stdout or stderr) into
    another stream, and to add a timestamp to each message printed.
    """

    def __init__(self, file1, file2):
        """Initializes the TeeWithTimestamp"""
        self.file1 = file1
        self.file2 = file2
        self.at_start_of_line = True

    def write(self, text):
        """Writes text to both files, prefixed with a timestamp"""

        if len(text):
            # Add timestamp if at the start of a line; also add [STDERR]
            # for stderr
            if self.at_start_of_line:
                now = datetime.datetime.now()
                prefix = now.strftime('[%H:%M:%S] ')
                if self.file1 == sys.__stderr__:
                    prefix += '[STDERR] '
                text = prefix + text

            self.file1.write(text)
            self.file2.write(text)

            self.at_start_of_line = (text[-1] == '\n')

The purpose is to add a timestamp to the beginning of each message, and to log everything to a log file. However, the problem I run into is that if I do this:

# log_file has already been opened
sys.stdout = TeeWithTimestamp(sys.stdout, log_file)

Then when I try to do print 'foo', I get a ValueError: I/O operation on closed file. I can't meaningfully call file.__init__() in my __init__(), since I don't want to open a new file, and I can't assign self.closed = False either, since it's a read-only attribute.

How can I modify this so that I can do print 'foo', and so that it supports all of the standard file attributes and methods?

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甩你一脸翔 2024-08-02 15:13:16

您也可以避免使用 super ：

class SuperFile(file):

    def __init__(self, *args, **kwargs):
        file.__init__(self, *args, **kwargs)

您将能够用它来编写。

You can as well avoid using super :

class SuperFile(file):

    def __init__(self, *args, **kwargs):
        file.__init__(self, *args, **kwargs)

You'll be able to write with it.

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流绪微梦 2024-08-02 15:13:15

调用 file.__init__ 是相当可行的（例如，在“/dev/null”上），但没有实际用途，因为您尝试覆盖 write 并没有“采取” print 语句的目的 - 当后者看到 sys.stdout 是 的实际实例时，它会在内部调用真正的 file.write >file （通过继承你就做到了这一点）。

除了write之外，print实际上并不需要任何其他方法，因此使您的类继承自object而不是file将工作。

如果您需要其他文件方法（即 print 不是您所做的全部），最好建议您自己实现它们。