A simple cron job parser...

cron.py

#!/usr/bin/env python

import sys
import datetime

class cronjob(object):
    def __init__(self, line):
        self.process_line(line)

    def process_line(self, line):
        m, h, dom, mon, dow, self.command = line.split(None, 5)

        self.minutes        = self.process_cronpart(m, 0, 59)
        self.hours          = self.process_cronpart(h, 0, 23)
        self.days_of_month  = self.process_cronpart(dom, 1, 31)
        self.months         = self.process_cronpart(mon, 1, 12)
        self.days_of_week   = self.process_cronpart(dow, 0, 6)

    def process_cronpart(self, spec, min, max):
        '''
        simple (broken) cronpart parser -- supports multiple ranges,
        modulo-style selectors, and the obvious * wildcard ...

        This recurses on itself to parse sub-parts after we've split off a
        selector as well.
        '''
        s = set()
        for part in spec.split(','):
            if '/' in part:
                # intentionally support things like */3/2 which selects */6 ...
                p, n = part.rsplit('/', 1)
                n = int(n)
                s.update(x for x in self.process_cronpart(p, min, max) if x % n == 0)
            elif '-' in part:
                a, b = part.split('-')
                s.update(range(int(a), int(b)+1, 1))
            elif part == '*':
                s.update(range(min, max+1, 1))
            else:
                s.add(int(part))
        return s

    def would_run(self, dt):
        if dt.minute in self.minutes and \
           dt.hour in self.hours and \
           dt.day in self.days_of_month and \
           dt.month in self.months and \
           dt.weekday() in self.days_of_week:
            return True
        return False

    @staticmethod
    def process_file(f):
        if isinstance(f, basestring):
            f = open(f)

        jobs = []
        for line in f:
            line = line.strip()
            if not line or line.startswith("#"):
                continue

            jobs.append(cronjob(line))
        return jobs

fname = sys.argv[1]
jobs = cronjob.process_file(fname)
dt = datetime.datetime.now()
end = dt + datetime.timedelta(days=7)
td = datetime.timedelta(minutes=1)

while dt < end:
    for job in jobs:
        if job.would_run(dt):
            print "Run:", dt, job.command
    dt += td