python檔案操作的方法介紹

檔案操作

1.open()函數

open()函數主要用於檔案處理，一般分為下面3個過程：

1.開啟檔案

2.操作檔

#3.關閉檔案

常見的格式範例：

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

1.開啟檔案

文件句柄 = open('文件路径','模式')

常見的模式有：

1.'r'，只讀

2.'w '，只寫（當對開啟執行只寫作業後，檔案原始內容將會被清空，注意備份）

#3.'a',追加

##"+"表示可以同時讀寫某個檔案

1.'r+'

2.'w+'

3.'a+'

“b”表示處理二進位檔案

1.'rb'，'rb+'

2.'wb','wb+'

3 .'ab','ab+'

"U"表示在讀取時，可以將\r \n \r\n自動轉換成\n （與r 或r+ 模式同使用）

1.'rU'

2.'r+U'

# 

2.操作檔

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操作檔

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操作檔

但其實常用的操作也就那幾個：

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(&#39;helloPython&#39;)
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

還有一個truncate()函數，用來截斷檔案內容

且只保留檔案內容截斷處之前的內容，不容易理解可以看範例：

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語句

上面利用open()函數進行文件處理時，必須在文件開啟進行操作後執行f.close()關閉文件，十分的麻煩。而使用with()語句則可以避免這一步驟繁瑣的操作，自動在檔案作業後關閉檔案。並且，在python中引入with語句的目的是在

異常處理中把try,except和finally關鍵字，以及與資源分配釋放相關的程式碼全部去掉，從而減少程式碼的編寫量，使程式碼更簡潔！

如：

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

等價於：

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

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