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"""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).
"""
import types
try:
from errno import EINVAL
except ImportError:
EINVAL = 22
__all__ = ["StringIO"]
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.
"""
def __init__(self, buf = ''):
# Force self.buf to be a string or unicode
if not isinstance(buf, types.StringTypes):
buf = str(buf)
self.buf = buf
self.len = len(buf)
self.buflist = []
self.pos = 0
self.closed = 0
self.softspace = 0
def __iter__(self):
return iter(self.readline, '')
def close(self):
"""Free the memory buffer.
"""
if not self.closed:
self.closed = 1
del self.buf, self.pos
def isatty(self):
if self.closed:
raise ValueError, "I/O operation on closed file"
return False
def seek(self, pos, mode = 0):
if self.closed:
raise ValueError, "I/O operation on closed file"
if self.buflist:
self.buf += ''.join(self.buflist)
self.buflist = []
if mode == 1:
pos += self.pos
elif mode == 2:
pos += self.len
self.pos = max(0, pos)
def tell(self):
if self.closed:
raise ValueError, "I/O operation on closed file"
return self.pos
def read(self, n = -1):
if self.closed:
raise ValueError, "I/O operation on closed file"
if self.buflist:
self.buf += ''.join(self.buflist)
self.buflist = []
if n < 0:
newpos = self.len
else:
newpos = min(self.pos+n, self.len)
r = self.buf[self.pos:newpos]
self.pos = newpos
return r
def readline(self, length=None):
if self.closed:
raise ValueError, "I/O operation on closed file"
if self.buflist:
self.buf += ''.join(self.buflist)
self.buflist = []
i = self.buf.find('\n', self.pos)
if i < 0:
newpos = self.len
else:
newpos = i+1
if length is not None:
if self.pos + length < newpos:
newpos = self.pos + length
r = self.buf[self.pos:newpos]
self.pos = newpos
return r
def readlines(self, sizehint = 0):
total = 0
lines = []
line = self.readline()
while line:
lines.append(line)
total += len(line)
if 0 < sizehint <= total:
break
line = self.readline()
return lines
def truncate(self, size=None):
if self.closed:
raise ValueError, "I/O operation on closed file"
if size is None:
size = self.pos
elif size < 0:
raise IOError(EINVAL, "Negative size not allowed")
elif size < self.pos:
self.pos = size
self.buf = self.getvalue()[:size]
def write(self, s):
if self.closed:
raise ValueError, "I/O operation on closed file"
if not s: return
# Force s to be a string or unicode
if not isinstance(s, types.StringTypes):
s = str(s)
if self.pos > self.len:
self.buflist.append('\0'*(self.pos - self.len))
self.len = self.pos
newpos = self.pos + len(s)
if self.pos < self.len:
if self.buflist:
self.buf += ''.join(self.buflist)
self.buflist = []
self.buflist = [self.buf[:self.pos], s, self.buf[newpos:]]
self.buf = ''
if newpos > self.len:
self.len = newpos
else:
self.buflist.append(s)
self.len = newpos
self.pos = newpos
def writelines(self, list):
self.write(''.join(list))
def flush(self):
if self.closed:
raise ValueError, "I/O operation on closed file"
def 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.
"""
if self.buflist:
self.buf += ''.join(self.buflist)
self.buflist = []
return self.buf
# A little test suite
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()`
print 'Position =', 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()
if __name__ == '__main__':
test()
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