Python3 文件操作基本语法
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
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1 f = open('lyrics') #打开文件 2 first_line = f.readline() 3 print('first line:',first_line) #读一行 4 print('我是分隔线'.center(50,'-')) 5 data = f.read()# 读取剩下的所有内容,文件大时不要用 6 print(data) #打印文件 7 8 f.close() #关闭文件
打开文件的模式有:
- r,只读模式(默认)。
- w,只写模式。【不可读;不存在则创建;存在则删除内容;】
- a,追加模式。【可读; 不存在则创建;存在则只追加内容;】
"+" 表示可以同时读写某个文件
- r+,可读写文件。【可读;可写;可追加】
- w+,写读
- a+,同a
"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)
- rU
- r+U
"b"表示处理二进制文件(如:FTP发送上传ISO镜像文件,linux可忽略,windows处理二进制文件时需标注)
- rb
- wb
- ab
其他语法
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1 def close(self): # real signature unknown; restored from __doc__ 2 """ 3 Close the file. 4 5 A closed file cannot be used for further I/O operations. close() may be 6 called more than once without error. 7 """ 8 pass 9 10 def fileno(self, *args, **kwargs): # real signature unknown 11 """ Return the underlying file descriptor (an integer). """ 12 pass 13 14 def isatty(self, *args, **kwargs): # real signature unknown 15 """ True if the file is connected to a TTY device. """ 16 pass 17 18 def read(self, size=-1): # known case of _io.FileIO.read 19 """ 20 注意,不一定能全读回来 21 Read at most size bytes, returned as bytes. 22 23 Only makes one system call, so less data may be returned than requested. 24 In non-blocking mode, returns None if no data is available. 25 Return an empty bytes object at EOF. 26 """ 27 return "" 28 29 def readable(self, *args, **kwargs): # real signature unknown 30 """ True if file was opened in a read mode. """ 31 pass 32 33 def readall(self, *args, **kwargs): # real signature unknown 34 """ 35 Read all data from the file, returned as bytes. 36 37 In non-blocking mode, returns as much as is immediately available, 38 or None if no data is available. Return an empty bytes object at EOF. 39 """ 40 pass 41 42 def readinto(self): # real signature unknown; restored from __doc__ 43 """ Same as RawIOBase.readinto(). """ 44 pass #不要用,没人知道它是干嘛用的 45 46 def seek(self, *args, **kwargs): # real signature unknown 47 """ 48 Move to new file position and return the file position. 49 50 Argument offset is a byte count. Optional argument whence defaults to 51 SEEK_SET or 0 (offset from start of file, offset should be >= 0); other values 52 are SEEK_CUR or 1 (move relative to current position, positive or negative), 53 and SEEK_END or 2 (move relative to end of file, usually negative, although 54 many platforms allow seeking beyond the end of a file). 55 56 Note that not all file objects are seekable. 57 """ 58 pass 59 60 def seekable(self, *args, **kwargs): # real signature unknown 61 """ True if file supports random-access. """ 62 pass 63 64 def tell(self, *args, **kwargs): # real signature unknown 65 """ 66 Current file position. 67 68 Can raise OSError for non seekable files. 69 """ 70 pass 71 72 def truncate(self, *args, **kwargs): # real signature unknown 73 """ 74 Truncate the file to at most size bytes and return the truncated size. 75 76 Size defaults to the current file position, as returned by tell(). 77 The current file position is changed to the value of size. 78 """ 79 pass 80 81 def writable(self, *args, **kwargs): # real signature unknown 82 """ True if file was opened in a write mode. """ 83 pass 84 85 def write(self, *args, **kwargs): # real signature unknown 86 """ 87 Write bytes b to file, return number written. 88 89 Only makes one system call, so not all of the data may be written. 90 The number of bytes actually written is returned. In non-blocking mode, 91 returns None if the write would block. 92 """ 93 pass
with语句
为了避免打开文件后忘记关闭,可以通过管理上下文,即:
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1 with open('log','r') as f: 2 3 ...
如此方式,当with代码块执行完毕时,内部会自动关闭并释放文件资源。
在Python 2.7 后,with又支持同时对多个文件的上下文进行管理,即:
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1 with open('log1') as obj1, open('log2') as obj2: 2 pass
为了更好