open函数，该函数用于文件处理

操作文件时，一般需要经历如下步骤：

打开文件

操作文件

一、打开文件

文件句柄 = open('文件路径', '模式')

打开文件时，需要指定文件路径和以何等方式打开文件，打开后，即可获取该文件句柄，日后通过此文件句柄对该文件操作。

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

二、操作

classfile(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()."""
return0def 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."""
returnFalsedef 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."""
passPython2.x
python2.x
classTextIOWrapper(_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)."""
passbuffer= 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
Python3.x
python3.x
python:open/文件操作
open/文件操作
f=open('/tmp/hello','w')
#open(路径+文件名,读写模式)
#读写模式:r只读,r+读写,w新建(会覆盖原有文件),a追加,b二进制文件.常用模式
如:'rb','wb','r+b'等等
读写模式的类型有：
rU 或 Ua 以读方式打开, 同时提供通用换行符支持 (PEP 278)
w 　　 以写方式打开，
a 　　 以追加模式打开 (从 EOF 开始, 必要时创建新文件)
r+ 　　以读写模式打开
w+　　以读写模式打开 (参见 w )
a+ 　 以读写模式打开 (参见 a )
rb 　 以二进制读模式打开
wb　　以二进制写模式打开 (参见 w )
ab 　 以二进制追加模式打开 (参见 a )
rb+　 以二进制读写模式打开 (参见 r+ )
wb+　 以二进制读写模式打开 (参见 w+ )
ab+ 　 以二进制读写模式打开 (参见 a+ )
========= ===============================================================
Character Meaning
--------- ---------------------------------------------------------------
'r' open for reading (default)
'w' open for writing, truncating the file first
'x' create a new file and open it for writing
'a' open for writing, appending to the end of the file if it exists
'b' binary mode
't' text mode (default)
'+' open a disk file for updating (reading and writing)
'U' universal newline mode (deprecated)
========= ===============================================================
注意：
1、使用'W'，文件若存在，首先要清空，然后（重新）创建，
2、使用'a'模式 ，把所有要写入文件的数据都追加到文件的末尾，即使你使用了seek（）指向文件的其他地方，如果文件不存在，将自动被创建。
f.read([size]) size未指定则返回整个文件,如果文件大小>2倍内存则有问题.f.read()读到文件尾时返回""(空字串)
file.readline() 返回一行
file.readline([size]) 返回包含size行的列表,size 未指定则返回全部行
for line in f: print line #通过迭代器访问
f.write("hello\n") #如果要写入字符串以外的数据,先将他转换为字符串.
f.tell() 返回一个整数,表示当前文件指针的位置(就是到文件头的比特数).
f.seek(偏移量,[起始位置])
用来移动文件指针
偏移量:单位:比特,可正可负
起始位置:0-文件头,默认值;1-当前位置;2-文件尾
f.close() 关闭文件
#!/usr/bin/env python
# Filename: using_file.py
poem='''\Programming is funWhen the work is doneif you wanna make your work also fun: use Python!'''
f=file('poem.txt','w') # open for 'w'riting
f.write(poem) # write text to file
f.close() # close the file
f=file('poem.txt')
# if no mode is specified, 'r'ead mode is assumed by default
while True:
line=f.readline()
if len(line)==0: # Zero length indicates EOF
break
print line,
# Notice comma to avoid automatic newline added by Python
f.close()
# close the file
三、管理上下文
为了避免打开文件后忘记关闭，可以通过管理上下文，即：
with open('log','r') as f:
...
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：
with open('log1') as obj1, open('log2') as obj2:
pass