homepage

The tarfile module's gettarinfo callable insists on stat'ing the file in question, preventing one from dynamically generating file content by passing a file-like object for addfile's fileobj argument.
I believe the attached patch fixes this issue. I generated the patch against 2.7 and tested it with 2.7, but it applies cleanly against 3.1 and "feels innocuous". I've also included my test code at the bottom of this comment.
Why would you want to do this? Imagine you've stored a file in three smaller files (perhaps to save the pieces on small external media, or as part of a deduplication system), with the content divided up into thirds. To subsequently put this file as a whole into a tar archive, it'd be nice if you could just create a file-like object to emit the catenation, rather than having to create a temporary file holding that catenation.
It's occurred to me that this should be done in a more object oriented style, but that feels a bit inconsistent given that fstat is in the os module, and not provided as an attribute of a file(-like) object. Comments?
Here's the test code:
#!/usr/local/cpython-2.7/bin/python
import os
import sys
import copy
import array
import stat_tarfile
def my_stat(filename):
 class mutable_stat:
 pass
 readonly_statobj = os.lstat(filename)
 mutable_statobj = mutable_stat()
 for attribute in dir(readonly_statobj):
 if not attribute.startswith('_'):
 value = getattr(readonly_statobj, attribute)
 setattr(mutable_statobj, attribute, value)
 return mutable_statobj
class generate_file_content:
 def __init__(self, number):
 self._multiplier = 100
 self._multipleno = 0
 self._number = str(number)
 self._buffer = ''
 def read(self, length):
 while self._multipleno < self._multiplier and len(self._buffer) < length:
 self._buffer += self._number
 self._multipleno += 1
 if self._buffer == '':
 return ''
 else:
 result = self._buffer[:length]
 self._buffer = self._buffer[length:]
 return result
def main():
 with stat_tarfile.open(fileobj = sys.stdout, mode = "w|") as tar:
 for number in xrange(100):
 #string = str(number) * 100
 fileobj = generate_file_content(number)
 statobj = my_stat('/etc/passwd')
 statobj.st_size = len(str(number)) * 100
 filename = 'file-%d.txt' % number
 tarinfo = tar.gettarinfo(filename, statobj = statobj)
 tarinfo.uid = 1000
 tarinfo.gid = 1000
 tarinfo.uname = "dstromberg"
 tarinfo.gname = "dstromberg"
 tar.addfile(tarinfo, fileobj)
main()

Hm, why don't you just do this:
with stat_tarfile.open(fileobj = sys.stdout, mode = "w|") as tar:
 for number in xrange(100):
 fileobj = generate_file_content(number)
 tarinfo = tar.gettarinfo(fileobj=open("/etc/passwd")) 
 tarinfo.name = 'file-%d.txt' % number
 tarinfo.size = len(str(number)) * 100
 tarinfo.uid = 1000
 tarinfo.gid = 1000
 tarinfo.uname = "dstromberg"
 tarinfo.gname = "dstromberg"
 tar.addfile(tarinfo, fileobj)
Wouldn't that work, too? Or am I missing something?