# -*- python -*-

'''

Open a file with three re-tries.

ABSTRACT

    On some networked filesystems, when dealing with tens of thousands
    of data files quickly, the remote system may run out of file handles
    or experience some other temporary problem.  Generally, these
    problems will reset immediately, but only after a file access has
    failed.  Rather than completely stop the process in the middle, and
    try to resume the process later, this code will try to hide the
    temporary problem.

    It forms a drop-in replacement for the core open() function.  When
    in use, any call to this ropen() will transparently try to open the
    file three times, with a short delay between each retry.

SYNOPSIS

    >>> from ropen import ropen as open

    >>> for x in xrange(100000):
    ...     f = open( flaky_network_file, 'r' )
    ...     f.close()

AUTHOR

    Ed Halley (ed@halley.cc) 10 September 2007

'''

import time
import random

_RANDOM = random.Random()

def ropen(*args):
    '''Drop-in replacement for core open() function.

    Allows three transparent retries to mask some network problems.
    '''
    raised = None
    retries = 3
    while retries > 0:
        retries -= 1
        try:
            return open(*args)
        except Exception, ex:
            raised = ex
            time.sleep(_RANDOM.random() + 0.25)
    raise raised