python subprocess Errno 24

'''Problems with file descriptors remaining open when making a LOT of 
subprocess calls can occasionally be solved by calling os.close() on
the file descriptor (returned by os.open() or pipe).'''


stdout, self.stderr = subprocess.Popen('primer3_core %s' % self.tf[1],\
shell=True, stdout=subprocess.PIPE, stdin=None, \
stderr=subprocess.PIPE, universal_newlines=True).communicate()

# make sure that we close the stupid ass input file or we're going
# to get the damn ValueError: filedescriptor out of range in select()
# or OSError: [Errno 24] Too many open files
os.close(self.tf[0]) 

you can add a new parameter "close_fds=True" in "Popen" to have a try.