小白跟着大神学Python——Day07 文件的操作

今日内容

文件操作

#三要素

1.path 文件的路径。可分为绝对路径和相对路径。

 

2.mode 模式，比如读，写，追加等等

# 1. 打开文件的模式有(默认为文本模式)：
r ，只读模式【默认模式，文件必须存在，不存在则抛出异常】
w，只写模式【不可读；不存在则创建；存在则清空内容】
a， 只追加写模式【不可读；不存在则创建；存在则只追加内容】
 
#2. 对于非文本文件，我们只能使用b模式，"b"表示以字节的方式操作
（而所有文件也都是以字节的形式存储的，使用这种模式无需考虑文本文件的字符编码、图片文件的格式、视频文件的格式）
rb
wb
ab
注：以b方式打开时，读取到的内容是字节类型，写入时也需要提供字节类型，不能指定编码
 
#3,‘+’模式（就是增加了一个功能）
r+， 读写【可读，可写】
w+，写读【可写，可读】
a+， 写读【可写，可读】
 
#4，以bytes类型操作的读写，写读，写读模式
r+b， 读写【可读，可写】
w+b，写读【可写，可读】
a+b， 写读【可写，可读】

 

# 3.encoding 编码方式，不同编码的文件需要根据原编码进行转化读取。

如果我们没有为open指定编码，操作系统会用自己的默认编码去打开文件，在windows下是gbk,在linux下是utf-8。

 

#1.打开文件，得到文件句柄并赋值给一个变量

#两种打开方法
1.f = open(r'd:\r111.txt',encoding= 'utf-8',mode='r') #要注意需要结合close

2.with open(r'd:\r111.txt',encoding= 'utf-8',mode='r') as f1,\
    open(r'd:\r112.txt',encoding= 'gbk',mode='r') as f2: #傻瓜式打开多个句柄，以及无需再输入close
 
#报错原因：
1.路径错误。 \与后面的那个字符产生了特殊意义（如d:\t）
2.UnicodeDecodeError: encoding 打开文件的编码与文件储存时的编码不一致。

 

#2.通过句柄对文件进行操作

2.1 常用操作方法
read（3）：
 
1. 文件打开方式为文本模式时，3代表读取3个字符
 
2. 文件打开方式为b模式时，3代表读取3个字节
 
其余的文件内光标移动都是以字节为单位的如：seek，tell，truncate
 
注意：
 
1. seek有三种移动方式0，1，2，其中1和2必须在b模式下进行，但无论哪种模式，都是以bytes为单位移动的。
 
2. truncate是截断文件，所以文件的打开方式必须可写，但是不能用w或w+等方式打开，因为那样直接清空文件了，
   所以truncate要在r+或a或a+等模式下测试效果。
 

 

2.2所有操作方法。

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

class TextIOWrapper(_TextIOBase):
"""
Character and line based layer over a BufferedIOBase object, buffer.
 
encoding gives the name of the encoding that the stream will be
decoded or encoded with. It defaults to locale.getpreferredencoding(False).
 
errors determines the strictness of encoding and decoding (see
help(codecs.Codec) or the documentation for codecs.register) and
defaults to "strict".
 
newline controls how line endings are handled. It can be None, '',
'\n', '\r', and '\r\n'. It works as follows:
 
* On input, if newline is None, universal newlines mode is
enabled. Lines in the input can end in '\n', '\r', or '\r\n', and
these are translated into '\n' before being returned to the
caller. If it is '', universal newline mode is enabled, but line
endings are returned to the caller untranslated. If it has any of
the other legal values, input lines are only terminated by the given
string, and the line ending is returned to the caller untranslated.
 
* On output, if newline is None, any '\n' characters written are
translated to the system default line separator, os.linesep. If
newline is '' or '\n', no translation takes place. If newline is any
of the other legal values, any '\n' characters written are translated
to the given string.
 
If line_buffering is True, a call to flush is implied when a call to
write contains a newline character.
"""
 
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
 
def __getstate__(self, *args, **kwargs): # real signature unknown
pass
 
def __init__(self, *args, **kwargs): # real signature unknown
pass
 
@staticmethod # known case of __new__
def __new__(*args, **kwargs): # real signature unknown
""" Create and return a new object. See help(type) for accurate signature. """
pass
 
def __next__(self, *args, **kwargs): # real signature unknown
""" Implement next(self). """
pass
 
def __repr__(self, *args, **kwargs): # real signature unknown
""" Return repr(self). """
pass
 
buffer = property(lambda self: object(), lambda self, v: None, lambda self: None) # default
 
closed = property(lambda self: object(), lambda self, v: None, lambda self: None) # default
 
encoding = property(lambda self: object(), lambda self, v: None, lambda self: None) # default
 
errors = property(lambda self: object(), lambda self, v: None, lambda self: None) # default
 
line_buffering = property(lambda self: object(), lambda self, v: None, lambda self: None) # default
 
name = property(lambda self: object(), lambda self, v: None, lambda self: None) # default
 
newlines = property(lambda self: object(), lambda self, v: None, lambda self: None) # default
 
_CHUNK_SIZE = property(lambda self: object(), lambda self, v: None, lambda self: None) # default
 
_finalizing = property(lambda self: object(), lambda self, v: None, lambda self: None) # default

 

#3.关闭文件

   close( ): #关闭文件

#关闭文件的注意事项：
打开一个文件包含两部分资源：操作系统级打开的文件+应用程序的变量。
在操作完毕一个文件时，必须把与该文件的这两部分资源一个不落地回收，回收方法为：
1、f.close() #回收操作系统级打开的文件
2、del f #回收应用程序级的变量
 
其中del f一定要发生在f.close()之后，否则就会导致操作系统打开的文件还没有关闭，白白占用资源，
而python自动的垃圾回收机制决定了我们无需考虑del f，这就要求我们，在操作完毕文件后，一定要记住f.close()

 

# 4.文件的修改

文件的数据是存放于硬盘上的，因而只存在覆盖、不存在修改这么一说，我们平时看到的修改文件，都是模拟出来的效果，大概的步骤可分为五步：

1.以读的模式打开原文件，产生文件句柄f1。
2.以写的模式打开新文件，产生文件句柄f2。
3.读取原文件将原文的内容改写成新内容写入新文件。
4.删除原文件。
5.将新文件重命名成原文件。

具体的说有两种实现方式：

方式一：将硬盘存放的该文件的内容全部加载到内存，在内存中是可以修改的，修改完毕后，再由内存覆盖到硬盘

import os # 调用系统模块
 
with open('a.txt') as read_f,open('.a.txt.swap','w') as write_f:
data=read_f.read() #全部读入内存,如果文件很大,会很卡
data=data.replace('alex','SB') #在内存中完成修改
 
write_f.write(data) #一次性写入新文件
 
os.remove('a.txt') #删除原文件
os.rename('.a.txt.swap','a.txt') #将新建的文件重命名为原文件

 

方式二：将硬盘存放的该文件的内容一行一行地读入内存，修改完毕就写入新文件，最后用新文件覆盖源文件

import os
 
with open('a.txt') as read_f,open('.a.txt.swap','w') as write_f:
for line in read_f:
line=line.replace('alex','SB')
write_f.write(line)
 
os.remove('a.txt')
os.rename('.a.txt.swap','a.txt')