import arcpy
import os
in_data = r"R:\natura 2000\8847.04 MaP\7517-341_Horber_Neckarhaenge\Daten_Offenland\2014-11-12_PE_Maßnahmenentwurf\Reperatur\Reperatur.gdb\data\massnahmen_anm56_141117"
field_list = []
numeric_fields = ["Double", "Integer", "SmallInteger"]
fields = arcpy.ListFields(in_data)
for field in fields:
# if (field.type in numeric_fields):
field_list.append(field.name)
# convert the list of fields to a semicolor delimited string
fields = ";".join(field_list)
rows = arcpy.UpdateCursor(in_data, '', '', fields)
count = len(field_list)
for row in rows:
for k in range(count):
if row.isNull(field_list):
row.setValue(field_list, 0)
rows.updateRow(row)