Re-forecasts: 1 param, 1 date 

#!/usr/bin/env python
from ecmwfapi import ECMWFDataServer
server = ECMWFDataServer()
server.retrieve({
    "class": "s2",
    "dataset": "s2s",
    "hdate": "1993-01-01",
    "date": "2014-12-01", 
    "expver": "prod",
    "levtype": "sfc",
    "origin": "lfpw",
    "param": "tp",
    "step": "24/to/1464/by/24",
    "stream": "enfh",
    "target": "CHANGEME",
    "time": "00",
    "type": "cf",
})
#!/usr/bin/env python
from ecmwfapi import ECMWFDataServer
server = ECMWFDataServer()
server.retrieve({
    "class": "s2",
    "dataset": "s2s",
    "hdate": "1993-01-01",
    "date": "2014-12-01", 
    "expver": "prod",
    "levtype": "sfc",
    "origin": "lfpw",
    "param": "tp",
    "step": "24/to/1464/by/24",
    "stream": "enfh",
    "target": "CHANGEME",
    "time": "00",
    "type": "pf",
    "number": "1/to/14",
})

Re- forecasts used to calibrate a  real-time forecast:

Retrieving one field (total precipitation here) for all time steps and  for all the re-forecasts used to calibrate the real-time forecast starting on 1 May 2015. For this request, all the re-forecasts starting on 1 May 1993-2014  are retrieved

#!/usr/bin/env python
from ecmwfapi import ECMWFDataServer
server = ECMWFDataServer()
server.retrieve({
 "class": "s2",
 "dataset": "s2s",
"hdate": "19930501/19940501/19950501/19960501/19970501/19980501/19990501/20000501/20010501/20020501/20030501/20040501/20050501/20060501/20070501/20080501/20090501/20100501/20110501/20120501/20130501/20140501",
 "expver": "prod",
 "levtype": "sfc",
 "origin": "lfpw",
 "param": "tp",
 "step": "24/to/1488/by/24",
 "stream": "enfh",
 "target": "CHANGEME",
 "time": "00",
 "type": "cf",
" date": "20141201",
})
#!/usr/bin/env python
from ecmwfapi import ECMWFDataServer
server = ECMWFDataServer()
server.retrieve({
 "class": "s2",
 "dataset": "s2s",
 "hdate": "19930501/19940501/19950501/19960501/19970501/19980501/19990501/20000501/20010501/20020501/20030501/20040501/20050501/20060501/20070501/20080501/20090501/20100501/20110501/20120501/20130501/20140501",
 "expver": "prod",
 "levtype": "sfc",
 "origin": "lfpw",
 "param": "tp",
 "step": "24/to/1464/by/24",
 "stream": "enfh",
 "target": "CHANGEME",
 "time": "00",
 "type": "pf",
 "number": "1/to/14",
" date": "20141201",
})