import arcpy
arcpy.env.workspace = "Path\Geodatabase.gdb"
inTable = "Table"

# Update data
with arcpy.da.UpdateCursor(inTable, ['field1']) as cursor:
for row in cursor:
# set value to field1
row[0] = 0
cursor.updateRow(row)

# Update view if necessary
# arcpy.RefreshActiveView()

 

# mind the Greek as unicode
with arcpy.da.UpdateCursor(inTable, ['munname', 'Sel1']) as cursor:
for row in cursor:
if row[0] == u'Δ. ΘΕΣΣΑΛΟΝΙΚΗΣ':
print(row[0])
# if munname = 'Δ. ΘΕΣΣΑΛΟΝΙΚΗΣ' then field Sel1 to 1
row[1] = 1
cursor.updateRow(row)

# Update view if necessary
arcpy.RefreshActiveView()