StringIO Namespace Reference

Data Structures
class	StringIO

Functions
def	test

Variables
int	EINVAL = 22
list	__all__ = ["StringIO"]

Detailed Description

File-like objects that read from or write to a string buffer.

This implements (nearly) all stdio methods.

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).

Function Documentation

def StringIO.test

(

)

Definition at line 176 of file StringIO.py.

References aifc.open().

def test():
    import sys
    if sys.argv[1:]:
        file = sys.argv[1]
    else:
        file = '/etc/passwd'
    lines = open(file, 'r').readlines()
    text = open(file, 'r').read()
    f = StringIO()
    for line in lines[:-2]:
        f.write(line)
    f.writelines(lines[-2:])
    if f.getvalue() != text:
        raise RuntimeError, 'write failed'
    length = f.tell()
    print 'File length =', length
    f.seek(len(lines[0]))
    f.write(lines[1])
    f.seek(0)
    print 'First line =', `f.readline()`
    here = f.tell()
    line = f.readline()
    print 'Second line =', `line`
    f.seek(-len(line), 1)
    line2 = f.read(len(line))
    if line != line2:
        raise RuntimeError, 'bad result after seek back'
    f.seek(len(line2), 1)
    list = f.readlines()
    line = list[-1]
    f.seek(f.tell() - len(line))
    line2 = f.read()
    if line != line2:
        raise RuntimeError, 'bad result after seek back from EOF'
    print 'Read', len(list), 'more lines'
    print 'File length =', f.tell()
    if f.tell() != length:
        raise RuntimeError, 'bad length'
    f.close()