run_if_dst_is

#!/usr/bin/env python2.7
"""
Run all following args iff DST for the Eastern Timezone
is in the position passed in as the first argument
called in the form
        run_if_dist_is on command args
        XOR
        run_if_dist_is off command args

"""
import subprocess
import sys

def is_dst(timezone="US/Eastern", date_override=None):
    """Determine whether or not Daylight Savings Time (DST)
    is currently in effect"""
    cmd = 'date'
    if date_override:
        cmd += ' --date="{0}"'.format(date_override)
    cmd += ' +%Z'
    out = subprocess.check_output(cmd,
        env={'TZ': timezone},
        stderr=subprocess.STDOUT,
        shell=True)
    # strip trailing newline
    # ending with DT is probably good enough for Central CDT and Eastern EDT
    return out.strip().endswith('DT')


def main(dst_flag, command_line_args):
    should_be_dst = None
    if dst_flag == "on":
        should_be_dst = True
    elif dst_flag == "off":
        should_be_dst = False
    else:
        raise Exception("Invalid call to run_if_dst_is, first arg must be 'on' or 'off'")

    if is_dst() == should_be_dst:
        return subprocess.call(command_line_args)

if __name__ == "__main__":
    sys.exit(main(sys.argv[1], sys.argv[2:]))