Python 模块学习 ---- StringIO
StringIO - File-like objects that read from or write to a string buffer.
StringIO经常被用来作为字符串的缓存，应为StringIO有个好处，他的有些接口和文件操作是一致的，也就是说用同样的代码，可以同时当成文件操作或者StringIO操作。下面取自python help
f = StringIO() # ready for writing
f = StringIO(buf) # ready for reading
f.close() # explicitly release resources held
flag = f.isatty() # always false
pos = f.tell() # get current position
f.seek(pos) # set current position
f.seek(pos, mode) # mode 0: absolute; 1: relative; 2: relative to EOF
buf = f.read() # read until EOF
buf = f.read(n) # read up to n bytes
buf = f.readline() # read until end of line ('\n') or EOF
list = f.readlines()# list of f.readline() results until EOF
f.truncate([size]) # truncate file at to at most size (default: current pos)
f.write(buf) # write at current position
f.writelines(list) # for line in list: f.write(line)
f.getvalue() # return whole file's contents as a string
Notes:
- Using a real file is often faster (but less convenient).
- There's also a much faster implementation in C, called cStringIO, but
it's not subclassable.
- fileno() is left unimplemented so that code which uses it triggers
an exception early.
- Seeking far beyond EOF and then writing will insert real null
bytes that occupy space in the buffer.
- There's a simple test set (see end of this file).
class StringIO
| class StringIO([buffer])
|
| When a StringIO object is created, it can be initialized to an existing
| string by passing the string to the constructor. If no string is given,
| the StringIO will start empty.
|
| The StringIO object can accept either Unicode or 8-bit strings, but
| mixing the two may take some care. If both are used, 8-bit strings that
| cannot be interpreted as 7-bit ASCII (that use the 8th bit) will cause
| a UnicodeError to be raised when getvalue() is called.
|
| Methods defined here:
|
| __init__(self, buf='')
|
| __iter__(self)
|
| close(self)
| Free the memory buffer.
|
| flush(self)
| Flush the internal buffer
|
| getvalue(self)
| Retrieve the entire contents of the "file" at any time before
| the StringIO object's close() method is called.
|
| The StringIO object can accept either Unicode or 8-bit strings,
| but mixing the two may take some care. If both are used, 8-bit
| strings that cannot be interpreted as 7-bit ASCII (that use the
| 8th bit) will cause a UnicodeError to be raised when getvalue()
| is called.
|
| isatty(self)
| Returns False because StringIO objects are not connected to a
| tty-like device.
|
| next(self)
| A file object is its own iterator, for example iter(f) returns f
| (unless f is closed). When a file is used as an iterator, typically
| in a for loop (for example, for line in f: print line), the next()
| method is called repeatedly. This method returns the next input line,
| or raises StopIteration when EOF is hit.
|
| read(self, n=-1)
| Read at most size bytes from the file
| (less if the read hits EOF before obtaining size bytes).
|
| If the size argument is negative or omitted, read all data until EOF
| is reached. The bytes are returned as a string object. An empty
| string is returned when EOF is encountered immediately.
|
| readline(self, length=None)
| Read one entire line from the file.
|
| A trailing newline character is kept in the string (but may be absent
| when a file ends with an incomplete line). If the size argument is
| present and non-negative, it is a maximum byte count (including the
| trailing newline) and an incomplete line may be returned.
|
| An empty string is returned only when EOF is encountered immediately.
|
| Note: Unlike stdio's fgets(), the returned string contains null
| characters ('\0') if they occurred in the input.
|
| readlines(self, sizehint=0)
| Read until EOF using readline() and return a list containing the
| lines thus read.
|
| If the optional sizehint argument is present, instead of reading up
| to EOF, whole lines totalling approximately sizehint bytes (or more
| to accommodate a final whole line).
|
| seek(self, pos, mode=0)
| Set the file's current position.
|
| The mode argument is optional and defaults to 0 (absolute file
| positioning); other values are 1 (seek relative to the current
| position) and 2 (seek relative to the file's end).
|
| There is no return value.
|
| tell(self)
| Return the file's current position.
|
| truncate(self, size=None)
| Truncate the file's size.
|
| If the optional size argument is present, the file is truncated to
| (at most) that size. The size defaults to the current position.
| The current file position is not changed unless the position
| is beyond the new file size.
|
| If the specified size exceeds the file's current size, the
| file remains unchanged.
|
| write(self, s)
| Write a string to the file.
|
| There is no return value.
|
| writelines(self, iterable)
| Write a sequence of strings to the file. The sequence can be any
| iterable object producing strings, typically a list of strings. There
| is no return value.
|
| (The name is intended to match readlines(); writelines() does not add
| line separators.)
import string
import StringIO
s = StringIO.StringIO()
s.write("aaaa")
lines = ['xxxxx', 'bbbbbbb']
s.writelines(lines)
s.seek(0)
print s.read()
print s.getvalue()
s.write(" ttttttttt ")
s.seek(0)
print s.readlines()
print s.len
