Python_day08_文件操作详解编程语言

#1. 打开文件，得到文件句柄并赋值给一个变量 
f = open('E:/Python/file/文件操作测试.txt', encoding='utf-8', mode='r') 
content = f.read() 
print(content) 
f.close() 
 
E:/Python/venv/Scripts/python.exe E:/Python/day08/文件操作.py 
文件操作测试读取，2018-3-27 
read 
 
f：变量，f_obj,file,f_handler,...文件句柄。 
open --- windows的系统功能， 
windows默认编码方式:gbk， 
linux默认编码方式:utf-8。 
f.close() --- 关闭文件（保存退出）

with open('a.txt', encoding='utf-8', 'w') as f: 
    pass 
 
with open('a.txt', encondig='utf-8', 'w') as read_f,open('b.txt','w') as write_f: 
    data=read_f.read() 
    write_f.write(data)

# f = open('log',encoding='utf-8') 
# for i in f: 
#     print(i.strip()) 
# f.close()

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（类似于文件-保存的效果） 
""" 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，并根据换行保存值到列表 
""" 
        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

--------------------------- 
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('old','new') #在内存中完成修改，将旧内容替换成新内容 
write_f.write(data) #一次性写入新文件 
os.remove('a.txt')  #删除原文件 
# 因为不删除将建立不了同名的文件，其实我感觉上先将原文件改名再让新文件命名成原文件名后确认无误后再删除原文件更安全保险。 
os.rename('.a.txt.swap','a.txt')   #将新建的文件重命名为原文件 
-----------------------------

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('old','new') 
write_f.write(line) 
os.remove('a.txt') 
os.rename('.a.txt.swap','a.txt') 

例：有如下文件： 
------- 
alex是老男孩python发起人，创建人。 
alex其实是人妖。 
谁说alex是sb？ 
你们真逗，alex再牛逼，也掩饰不住资深屌丝的气质。 
---------- 
将文件中所有的alex都替换成大写的SB。 
答： 
with open('log',encoding='utf-8') as f1,/ 
open('log.bak',encoding='utf-8',mode='w') as f2: 
content = f1.read() 
new_content = content.replace('alex','SB') 
f2.write(new_content) 
os.remove('log') 
os.rename('log.bak','log') 
import os 
with open('log',encoding='utf-8') as f1,/ 
open('log.bak',encoding='utf-8',mode='w') as f2: 
for i in f1: 
new_i = i.replace('SB','alex') 
f2.write(new_i) 
os.remove('log') 
os.rename('log.bak','log')