summing up python dictionary values: add all values, where type='+' should be added, type='-' should be subtracted and other type should be ignored

sum_dict_switch.py

# define entries
entries = [{'type': '+', 'value': 9},\
  {'type': '+', 'value': 12.3},\
  {'type': '-', 'value': 4},\
  {'type': '+', 'value': 0.89},\
  {'type': '-', 'value': 2.65},\
  {'type': '-', 'value': 14.3},\
  {'type': '+', 'value': 6.8},\
  {'type': 'unknown', 'value': 200}]

# use functional dictionary as a switch-case statement replacement

def add(arg):
  return arg

def sub(arg):
  return -arg

functions = {"+": add, "-": sub}

print sum([functions[x['type']](x['value']) for x in entries if functions.has_key(x['type'])])

sum_dict_ternary.py

# define entries
entries = [{'type': '+', 'value': 9},\
  {'type': '+', 'value': 12.3},\
  {'type': '-', 'value': 4},\
  {'type': '+', 'value': 0.89},\
  {'type': '-', 'value': 2.65},\
  {'type': '-', 'value': 14.3},\
  {'type': '+', 'value': 6.8},\
  {'type': 'unknown', 'value': 200}]

# use nested ternary operator (X if Y else Z)
print sum([x['value'] if x['type'] == '+' else (-x['value'] if x['type'] == '-' else 0) for x in entries])