day7文件操作
一、对文件操作流程
- 打开文件，得到文件句柄并赋值给一个变量
- 通过句柄对文件进行操作
- 关闭文件
#1. 打开文件，得到文件句柄并赋值给一个变量 f=open('a.txt','r',encoding='utf-8') #默认打开模式就为r #2. 通过句柄对文件进行操作 data=f.read() #3. 关闭文件 f.close()
二、关闭文件注意事项：
1 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： 2 1、f.close() #回收操作系统级打开的文件 3 2、del f #回收应用程序级的变量 4 5 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， 6 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() 7 8 虽然我这么说，但是很多同学还是会很不要脸地忘记f.close(),对于这些不长脑子的同学，我们推荐傻瓜式操作方式：使用with关键字来帮我们管理上下文 9 with open('a.txt','w') as f: 10 pass 11 12 with open('a.txt','r') as read_f,open('b.txt','w') as write_f: 13 data=read_f.read() 14 write_f.write(data)
三、文件编码：
f=open(...)是由操作系统打开文件，那么如果我们没有为open指定编码，那么打开文件的默认编码很明显是操作系统说了算了，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。
四、文件的打开模式
文件句柄 = open（‘文件路径’，‘模式‘’ 编码形式）
#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jgp格式、视频文件的avi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】
五、文件的操作方式
5.1、常见操作方法
read（3）：
1. 文件打开方式为文本模式时，代表读取3个字符
2. 文件打开方式为b模式时，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
seek（0）将光标调整到文件开头 seek（0,2）将光标调整到文件末尾
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。
5.2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
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 '\n', '\r', and '\r\n'. 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 '\n', '\r', or '\r\n', and 17 these are translated into '\n' 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 '\n' characters written are 24 translated to the system default line separator, os.linesep. If 25 newline is '' or '\n', no translation takes place. If newline is any 26 of the other legal values, any '\n' 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
六、文件的修改
# 修改文件五部曲 ''' 1、将原文件读取到内存 2、创建一个新的文件 3、将原内容修改为新内容 4、将源文件删除 5、将新文件重命名为原文件 '''
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（word，vim，nodpad++等编辑器）
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')
方法三：在原文件里对文件进行修改（即只打开一个需要修改的文件，不调用系统os文件做删除覆盖操作）
with open('test1','r+',encoding='utf-8') as f: date = f.read() new_date = date.replace('alex','SB') f.seek(0) f.truncate() f.write(new_date)
