I came across a complaint that PEP 0042 had become a graveyard of
neglected ideas, and decided to have a look through and implement
something. Creating a smarter temporary file object seemed simple
enough.
Oddly, even after GvR re-opened it, I can't post an attachment to that
tracker item (it's under "Feature Requests" -- does it need to get moved
to "Patches" first?), but the implementation is short, so it's included
below. This is intended to be appended to Lib/tempfile.py (and thus
assumes that module's globals are present).
I would appreciate it if the gurus of python-dev could take a peek and
let me know if this is unsuitable or incorrect for any reason. It's not
the most straightforward implementatio -- I used the optimization
techniques I found in TemporaryFile.
If this looks good, I'll prepare a patch against trunk, including an
additional chunk of documentation and a unit test.
Dustin
-----cut-here-----
try:
from cStringIO import StringIO
except:
from StringIO import StringIO
class SpooledTemporaryFile:
"""Temporary file wrapper, specialized to switch from
StringIO to a real file when it exceeds a certain size or
when a fileno is needed.
"""
_rolled = False
def __init__(self, max_size=0, mode='w+b', bufsize=-1,
suffix="", prefix=template, dir=None):
self._file = StringIO()
self._max_size = max_size
self._TemporaryFileArgs = (mode, bufsize, suffix, prefix, dir)
def _check(self, file):
if self._rolled: return
if file.tell() > self.__dict__['_max_size']:
self._rollover(file)
def _rollover(self, file):
args = self.__dict__['_TemporaryFileArgs']
self.__dict__.clear() # clear attributes cached by __getattr__
newfile = self._file = TemporaryFile(*args)
newfile.write(file.getvalue())
newfile.seek(file.tell(), 0)
self._rolled = True
# replace patched functions with the new file's methods
self.write = newfile.write
self.writelines = newfile.writelines
self.fileno = newfile.fileno
def write(self, s):
file = self.__dict__['_file']
rv = file.write(s)
self._check(file)
return rv
def writelines(self, iterable):
file = self.__dict__['_file']
rv = file.writelines(iterable)
self._check(file)
return rv
def fileno(self):
self._rollover(self.__dict__['_file'])
return self.fileno()
def __getattr__(self, name):
file = self.__dict__['_file']
a = getattr(file, name)
if type(a) != type(0):
setattr(self, name, a)
return a
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