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  • Python基础七文件操作

     
     一、昨日内容回顾
            数据类型补充：
            str <--> list    split    join
            同一个代码块的缓存机制：
            适用的数据类型：str int bool
            小数据池（也是一种缓存机制）：
            适用的数据类型：int（-5~256）str（符合一定规则的）bool
            小数据池缓存机制和同一个代码块的缓存机制的意义：节省内存，提高性能
            编码进阶——转换
    二、文件操作
            初识：
                如果想要通过python代码操作这个文件：必要的三要素：
                    1、path：即文件路径
                    2、mode：即模式 r w r+ w+ a ......
                    3、encoding：编码方式
    　　　　以上就是open()方法所需要的参数其中mode参数默认mode='r'
           读（r rb r+ r+b）：
                r模式下的物种读取方式：
    read()
    全部读取  
    read(n)
    按照字符读取（rb模式下按照字节读取）
    readline()
    按行读取
    readlines()
    返回一个列表，每个元素是原文件的每行数据
    for循环
    # file_handler = open('test.txt', mode='r+', encoding='utf-8')
    # for line in file_handler:
    # print(line.strip())
    # file_handler.close()
                rb模式下的物种读取方式：
    read()
    全部读取  
    read(n)
    按照字节读取（r模式下按照字符读取）
    readline()
    按行读取
    readlines()
    返回一个列表，每个元素是原文件的每行数据
    for循环
    # file_handler = open('test.txt', mode='rb')
    # for line in file_handler:
    # print(line.strip())
    # file_handler.close()
                    b模式操作的文件是非文字类的文件：图片，视频，音频等的
      　　r+模式，应该先读后写
    　　　　那如果先写后读呢？
        　　　　这涉及一个光标的问题，需要调整光标。      用seek方法调整光标位置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
            写（w wb w+ w+b）　
      　　 w模式必须以字符串的内容写入
                    有文件先清空写入，没有文件创造文件写入
     　　w+模式，先写后读，做完写的操作后，光标已经移动到文件的最后位置，所以如果后面再读的话，读不出内容，要通过调整光标解决这个问题
            追加（a ab a+ a+b）
    分析一下这串代码：
    f1 = open('d:诶呀学习好有趣.ext', endoding = 'utf-8', mode= 'r')
countent = f1.read()
print(countent)
f.close()
    f1 f file file_handler f_h......这些叫文件句柄
    open()内置函数 这个函数实际上是调用的操作系统的对文件操作的功能
    Windows：默认的编码是gbk
    linux：默认的编码方式是utf-8
    IOS：默认的编码方式是utf-8
    接下来你对文件进行的任何操作，都需要借助文件句柄操作
    f.close()
    Python打开一个文件总共分三步：
    第一步：打开文件产生文件句柄
    第二步：对文件句柄进行操作
    第三步：关闭文件句柄
    python文件方法中有一种傻瓜式的骚操作，不用手动关闭文件句柄（会自动关闭），并且可以同一语句操作创建多个文件句柄：
      文件的改（当前几乎所有的文件编辑软件都是这种套路）：
                1.以读的模式打开原文件产生文件句柄f1
                2.以写的模式打开一个新文件产生文件句柄f2
                3.读取原文件，将原文件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
    python的实现方式：
     1 import os  # 调用系统模块
 2 
 3 with open('a.txt') as read_f,open('.a.txt.swap','w') as write_f:
 4     data=read_f.read() #全部读入内存,如果文件很大,会很卡
 5     data=data.replace('alex','SB') #在内存中完成修改
 6 
 7     write_f.write(data) #一次性写入新文件
 8 
 9 os.remove('a.txt')  #删除原文件
10 os.rename('.a.txt.swap','a.txt')   #将新建的文件重命名为原文件
    方法一
    升级版
    1 import os
2 
3 with open('a.txt') as read_f,open('.a.txt.swap','w') as write_f:
4     for line in read_f:
5         line=line.replace('alex','SB')
6         write_f.write(line)
7 
8 os.remove('a.txt')
9 os.rename('.a.txt.swap','a.txt')
    方法二
    萌新的常见报错原因：
    1、路径报错。与后面的字符产生了特殊意义。
            解决方式：

     2、unicodedecodeerror：编码问题
            解决方式：用什么编码存储的文件就要用什么编码进行操作
    3、encodding 只是声明了此文件的需要用什么编码本解码而已
    补充知识点：
            绝对路径：从磁盘（根目录）开始，直到找到文件。
            相对路径：当前路径（当前文件夹）找到的文件
     文件的其他操作：
      1 class file(object)
  2     def close(self): # real signature unknown; restored from __doc__
  3         关闭文件
  4         """
  5         close() -> None or (perhaps) an integer.  Close the file.
  6          
  7         Sets data attribute .closed to True.  A closed file cannot be used for
  8         further I/O operations.  close() may be called more than once without
  9         error.  Some kinds of file objects (for example, opened by popen())
 10         may return an exit status upon closing.
 11         """
 12  
 13     def fileno(self): # real signature unknown; restored from __doc__
 14         文件描述符  
 15          """
 16         fileno() -> integer "file descriptor".
 17          
 18         This is needed for lower-level file interfaces, such os.read().
 19         """
 20         return 0    
 21  
 22     def flush(self): # real signature unknown; restored from __doc__
 23         刷新文件内部缓冲区
 24         """ flush() -> None.  Flush the internal I/O buffer. """
 25         pass
 26  
 27  
 28     def isatty(self): # real signature unknown; restored from __doc__
 29         判断文件是否是同意tty设备
 30         """ isatty() -> true or false.  True if the file is connected to a tty device. """
 31         return False
 32  
 33  
 34     def next(self): # real signature unknown; restored from __doc__
 35         获取下一行数据，不存在，则报错
 36         """ x.next() -> the next value, or raise StopIteration """
 37         pass
 38  
 39     def read(self, size=None): # real signature unknown; restored from __doc__
 40         读取指定字节数据
 41         """
 42         read([size]) -> read at most size bytes, returned as a string.
 43          
 44         If the size argument is negative or omitted, read until EOF is reached.
 45         Notice that when in non-blocking mode, less data than what was requested
 46         may be returned, even if no size parameter was given.
 47         """
 48         pass
 49  
 50     def readinto(self): # real signature unknown; restored from __doc__
 51         读取到缓冲区，不要用，将被遗弃
 52         """ readinto() -> Undocumented.  Don't use this; it may go away. """
 53         pass
 54  
 55     def readline(self, size=None): # real signature unknown; restored from __doc__
 56         仅读取一行数据
 57         """
 58         readline([size]) -> next line from the file, as a string.
 59          
 60         Retain newline.  A non-negative size argument limits the maximum
 61         number of bytes to return (an incomplete line may be returned then).
 62         Return an empty string at EOF.
 63         """
 64         pass
 65  
 66     def readlines(self, size=None): # real signature unknown; restored from __doc__
 67         读取所有数据，并根据换行保存值列表
 68         """
 69         readlines([size]) -> list of strings, each a line from the file.
 70          
 71         Call readline() repeatedly and return a list of the lines so read.
 72         The optional size argument, if given, is an approximate bound on the
 73         total number of bytes in the lines returned.
 74         """
 75         return []
 76  
 77     def seek(self, offset, whence=None): # real signature unknown; restored from __doc__
 78         指定文件中指针位置
 79         """
 80         seek(offset[, whence]) -> None.  Move to new file position.
 81          
 82         Argument offset is a byte count.  Optional argument whence defaults to
 83 (offset from start of file, offset should be >= 0); other values are 1
 84         (move relative to current position, positive or negative), and 2 (move
 85         relative to end of file, usually negative, although many platforms allow
 86         seeking beyond the end of a file).  If the file is opened in text mode,
 87         only offsets returned by tell() are legal.  Use of other offsets causes
 88         undefined behavior.
 89         Note that not all file objects are seekable.
 90         """
 91         pass
 92  
 93     def tell(self): # real signature unknown; restored from __doc__
 94         获取当前指针位置
 95         """ tell() -> current file position, an integer (may be a long integer). """
 96         pass
 97  
 98     def truncate(self, size=None): # real signature unknown; restored from __doc__
 99         截断数据，仅保留指定之前数据
100         """
101         truncate([size]) -> None.  Truncate the file to at most size bytes.
102          
103         Size defaults to the current file position, as returned by tell().
104         """
105         pass
106  
107     def write(self, p_str): # real signature unknown; restored from __doc__
108         写内容
109         """
110         write(str) -> None.  Write string str to file.
111          
112         Note that due to buffering, flush() or close() may be needed before
113         the file on disk reflects the data written.
114         """
115         pass
116  
117     def writelines(self, sequence_of_strings): # real signature unknown; restored from __doc__
118         将一个字符串列表写入文件
119         """
120         writelines(sequence_of_strings) -> None.  Write the strings to the file.
121          
122         Note that newlines are not added.  The sequence can be any iterable object
123         producing strings. This is equivalent to calling write() for each string.
124         """
125         pass
126  
127     def xreadlines(self): # real signature unknown; restored from __doc__
128         可用于逐行读取文件，非全部
129         """
130         xreadlines() -> returns self.
131          
132         For backward compatibility. File objects now include the performance
133         optimizations previously implemented in the xreadlines module.
134         """
135         pass
136 
137 2.x
    2.x
      1 class TextIOWrapper(_TextIOBase):
  2     """
  3     Character and line based layer over a BufferedIOBase object, buffer.
  4     
  5     encoding gives the name of the encoding that the stream will be
  6     decoded or encoded with. It defaults to locale.getpreferredencoding(False).
  7     
  8     errors determines the strictness of encoding and decoding (see
  9     help(codecs.Codec) or the documentation for codecs.register) and
 10     defaults to "strict".
 11     
 12     newline controls how line endings are handled. It can be None, '',
 13     '
', '
', and '
'.  It works as follows:
 14     
 15     * On input, if newline is None, universal newlines mode is
 16       enabled. Lines in the input can end in '
', '
', or '
', and
 17       these are translated into '
' before being returned to the
 18       caller. If it is '', universal newline mode is enabled, but line
 19       endings are returned to the caller untranslated. If it has any of
 20       the other legal values, input lines are only terminated by the given
 21       string, and the line ending is returned to the caller untranslated.
 22     
 23     * On output, if newline is None, any '
' characters written are
 24       translated to the system default line separator, os.linesep. If
 25       newline is '' or '
', no translation takes place. If newline is any
 26       of the other legal values, any '
' characters written are translated
 27       to the given string.
 28     
 29     If line_buffering is True, a call to flush is implied when a call to
 30     write contains a newline character.
 31     """
 32     def close(self, *args, **kwargs): # real signature unknown
 33         关闭文件
 34         pass
 35 
 36     def fileno(self, *args, **kwargs): # real signature unknown
 37         文件描述符  
 38         pass
 39 
 40     def flush(self, *args, **kwargs): # real signature unknown
 41         刷新文件内部缓冲区
 42         pass
 43 
 44     def isatty(self, *args, **kwargs): # real signature unknown
 45         判断文件是否是同意tty设备
 46         pass
 47 
 48     def read(self, *args, **kwargs): # real signature unknown
 49         读取指定字节数据
 50         pass
 51 
 52     def readable(self, *args, **kwargs): # real signature unknown
 53         是否可读
 54         pass
 55 
 56     def readline(self, *args, **kwargs): # real signature unknown
 57         仅读取一行数据
 58         pass
 59 
 60     def seek(self, *args, **kwargs): # real signature unknown
 61         指定文件中指针位置
 62         pass
 63 
 64     def seekable(self, *args, **kwargs): # real signature unknown
 65         指针是否可操作
 66         pass
 67 
 68     def tell(self, *args, **kwargs): # real signature unknown
 69         获取指针位置
 70         pass
 71 
 72     def truncate(self, *args, **kwargs): # real signature unknown
 73         截断数据，仅保留指定之前数据
 74         pass
 75 
 76     def writable(self, *args, **kwargs): # real signature unknown
 77         是否可写
 78         pass
 79 
 80     def write(self, *args, **kwargs): # real signature unknown
 81         写内容
 82         pass
 83 
 84     def __getstate__(self, *args, **kwargs): # real signature unknown
 85         pass
 86 
 87     def __init__(self, *args, **kwargs): # real signature unknown
 88         pass
 89 
 90     @staticmethod # known case of __new__
 91     def __new__(*args, **kwargs): # real signature unknown
 92         """ Create and return a new object.  See help(type) for accurate signature. """
 93         pass
 94 
 95     def __next__(self, *args, **kwargs): # real signature unknown
 96         """ Implement next(self). """
 97         pass
 98 
 99     def __repr__(self, *args, **kwargs): # real signature unknown
100         """ Return repr(self). """
101         pass
102 
103     buffer = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default
104 
105     closed = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default
106 
107     encoding = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default
108 
109     errors = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default
110 
111     line_buffering = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default
112 
113     name = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default
114 
115     newlines = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default
116 
117     _CHUNK_SIZE = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default
118 
119     _finalizing = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default
120 
121 3.x
    3.x
     
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  • 原文地址：https://www.cnblogs.com/gzying-01/p/10183944.html
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