文件操作

1.open()函数

open()函数主要用于文件处理，一般分为下面3个过程：

1.打开文件2.操作文件3.关闭文件

常见的格式示例：

f = open('note.txt','r')
f.read()
f.close()

1.打开文件

文件句柄 = open('文件路径','模式')

常见的模式有：

1.‘r’，只读

2.‘w’，只写（当对打开执行只写操作后，文件原内容将会被清空，注意备份）

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3.‘a’,追加

"+" 表示可以同时读写某个文件

1.‘r+’

2.‘w+’

3.‘a+’

“b”表示处理二进制文件

1.‘rb’，‘rb+’

2.‘wb’,‘wb+’

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3.‘ab’,‘ab+’

"U"表示在读取时，可以将 \r \n \r\n自动转换成 \n （与 r 或 r+ 模式同使用）

1.‘rU’

2.‘r+U’

2.操作文件

class file(object)
    def close(self): # real signature unknown; restored from __doc__
        关闭文件
        """
        close() -> None or (perhaps) an integer.  Close the file.

        Sets data attribute .closed to True.  A closed file cannot be used for
        further I/O operations.  close() may be called more than once without
        error.  Some kinds of file objects (for example, opened by popen())
        may return an exit status upon closing.
        """

    def fileno(self): # real signature unknown; restored from __doc__
        文件描述符
         """
        fileno() -> integer "file descriptor".

        This is needed for lower-level file interfaces, such os.read().
        """
        return 0

    def flush(self): # real signature unknown; restored from __doc__
        刷新文件内部缓冲区
        """ flush() -> None.  Flush the internal I/O buffer. """
        pass


    def isatty(self): # real signature unknown; restored from __doc__
        判断文件是否是同意tty设备
        """ isatty() -> true or false.  True if the file is connected to a tty device. """
        return False


    def next(self): # real signature unknown; restored from __doc__
        获取下一行数据，不存在，则报错
        """ x.next() -> the next value, or raise StopIteration """
        pass

    def read(self, size=None): # real signature unknown; restored from __doc__
        读取指定字节数据
        """
        read([size]) -> read at most size bytes, returned as a string.

        If the size argument is negative or omitted, read until EOF is reached.
        Notice that when in non-blocking mode, less data than what was requested
        may be returned, even if no size parameter was given.
        """
        pass

    def readinto(self): # real signature unknown; restored from __doc__
        读取到缓冲区，不要用，将被遗弃
        """ readinto() -> Undocumented.  Don't use this; it may go away. """
        pass

    def readline(self, size=None): # real signature unknown; restored from __doc__
        仅读取一行数据
        """
        readline([size]) -> next line from the file, as a string.

        Retain newline.  A non-negative size argument limits the maximum
        number of bytes to return (an incomplete line may be returned then).
        Return an empty string at EOF.
        """
        pass

    def readlines(self, size=None): # real signature unknown; restored from __doc__
        读取所有数据，并根据换行保存值列表
        """
        readlines([size]) -> list of strings, each a line from the file.

        Call readline() repeatedly and return a list of the lines so read.
        The optional size argument, if given, is an approximate bound on the
        total number of bytes in the lines returned.
        """
        return []

    def seek(self, offset, whence=None): # real signature unknown; restored from __doc__
        指定文件中指针位置
        """
        seek(offset[, whence]) -> None.  Move to new file position.

        Argument offset is a byte count.  Optional argument whence defaults to
(offset from start of file, offset should be >= 0); other values are 1
        (move relative to current position, positive or negative), and 2 (move
        relative to end of file, usually negative, although many platforms allow
        seeking beyond the end of a file).  If the file is opened in text mode,
        only offsets returned by tell() are legal.  Use of other offsets causes
        undefined behavior.
        Note that not all file objects are seekable.
        """
        pass

    def tell(self): # real signature unknown; restored from __doc__
        获取当前指针位置
        """ tell() -> current file position, an integer (may be a long integer). """
        pass

    def truncate(self, size=None): # real signature unknown; restored from __doc__
        截断数据，仅保留指定之前数据
        """
        truncate([size]) -> None.  Truncate the file to at most size bytes.

        Size defaults to the current file position, as returned by tell().
        """
        pass

    def write(self, p_str): # real signature unknown; restored from __doc__
        写内容
        """
        write(str) -> None.  Write string str to file.

        Note that due to buffering, flush() or close() may be needed before
        the file on disk reflects the data written.
        """
        pass

    def writelines(self, sequence_of_strings): # real signature unknown; restored from __doc__
        将一个字符串列表写入文件
        """
        writelines(sequence_of_strings) -> None.  Write the strings to the file.

        Note that newlines are not added.  The sequence can be any iterable object
        producing strings. This is equivalent to calling write() for each string.
        """
        pass

    def xreadlines(self): # real signature unknown; restored from __doc__
        可用于逐行读取文件，非全部
        """
        xreadlines() -> returns self.

        For backward compatibility. File objects now include the performance
        optimizations previously implemented in the xreadlines module.
        """
        pass

Python 2.x

python2操作文件

class TextIOWrapper(_TextIOBase):
    """
    def close(self, *args, **kwargs): # real signature unknown
        关闭文件
        pass

    def fileno(self, *args, **kwargs): # real signature unknown
        文件描述符
        pass

    def flush(self, *args, **kwargs): # real signature unknown
        刷新文件内部缓冲区
        pass

    def isatty(self, *args, **kwargs): # real signature unknown
        判断文件是否是同意tty设备
        pass

    def read(self, *args, **kwargs): # real signature unknown
        读取指定字节数据
        pass

    def readable(self, *args, **kwargs): # real signature unknown
        是否可读
        pass

    def readline(self, *args, **kwargs): # real signature unknown
        仅读取一行数据
        pass

    def seek(self, *args, **kwargs): # real signature unknown
        指定文件中指针位置
        pass

    def seekable(self, *args, **kwargs): # real signature unknown
        指针是否可操作
        pass

    def tell(self, *args, **kwargs): # real signature unknown
        获取指针位置
        pass

    def truncate(self, *args, **kwargs): # real signature unknown
        截断数据，仅保留指定之前数据
        pass

    def writable(self, *args, **kwargs): # real signature unknown
        是否可写
        pass

    def write(self, *args, **kwargs): # real signature unknown
        写内容
        pass

Python 3.x

python3操作文件

但其实常用的操作也就那几个：

f.read(3)   # python2中表示指定读取3个字节，python3中表示指定读取3个字符！
f.readline()    # 读取文件内容中的一行
f.readlines()   # 自动将文件内容解析为一个< 行的列表 >，可以用 for line in f.readlines(): 处理
f.write('helloPython')
f.seek(9)   # 按照字节来执行，用来指定当前文件指针位置,seek(0)表示文件指针移到文件头，seek(0,2)指向文件尾，便于追加内容
f.tell()    # 是按照字节来执行的，用来查看当前指针位置

还有一个truncate()函数，用于截断文件内容且仅保留文件内容截断处之前的内容，不容易理解可以看示例：

f = open('test.log','r+',encoding='utf-8')
#  encoding='utf-8'，有处理汉字的时候这样用
f.seek(9)
#   原文件内容是‘小苹果helloPython’
f.truncate()
#执行truncate()后，仅保留原文件截断之前的内容，这里即为‘小苹果’
f.close()

2.with语句

上面利用open()函数进行文件处理时，必须在文件打开进行操作后执行f.close()关闭文件，十分的麻烦。而使用with()语句则可以避免这一步繁琐的操作，自动在文件操作后关闭文件。并且，在python中引入with语句的目的是在异常处理中把try,except和finally关键字，以及与资源分配释放相关的代码全部去掉，从而减少代码的编写量，使代码更简洁！

如：

with open('name.txt', 'w') as f:
    f.write('Somebody^Fancy1')

等价于：

try:
    f = open('name.txt','w')
    f.write('Somebody^Fancy1')
finally:
    if f:
        f.close()