Python函数使用return后调用无输出问题排查求助

核心问题分析 #

• print语句永远不会执行
  函数里的return cities是函数的出口，一旦执行到这一行，函数会立刻返回结果并终止运行，后面的print(cities)根本没机会被执行。

• 调用函数时未处理返回值
  你执行countCities(cities1, cities2, cities3)时，函数确实会返回统计好的字典，但你没有把这个返回值打印出来，所以控制台不会有任何输出。和全局变量无关，是你没主动输出返回结果。

解决办法 #

方法一：调整print和return的顺序 #

如果想在函数内部直接打印结果，把print移到return前面：

def countCities(c1, c2, c3):
  cities = {"eu": 0, 
  "as": 0,
  "am": 0,
  "sa": 0,
  "af": 0}
  for x in c1 + c2 + c3:
    code = x.split("-")[-1]
    if code in cities:
      cities[code] += 1
  print(cities)  # 先打印再返回结果
  return cities

cities1 = ["london-eu","bangkok-as", "madrid-eu"]
cities2 = ["paris-eu","milan-eu", "madrid-eu", "budapest-eu"]
cities3 = ["houston-am","milan-eu", "bogota-sa", "nairobi-af"]

countCities(cities1, cities2, cities3)

方法二：调用函数时打印返回值 #

保持函数的return逻辑不变，在调用时主动打印函数的返回结果：

def countCities(c1, c2, c3):
  cities = {"eu": 0, 
  "as": 0,
  "am": 0,
  "sa": 0,
  "af": 0}
  for x in c1 + c2 + c3:
    code = x.split("-")[-1]
    if code in cities:
      cities[code] += 1
  return cities

cities1 = ["london-eu","bangkok-as", "madrid-eu"]
cities2 = ["paris-eu","milan-eu", "madrid-eu", "budapest-eu"]
cities3 = ["houston-am","milan-eu", "bogota-sa", "nairobi-af"]

# 调用函数并打印返回的统计结果
print(countCities(cities1, cities2, cities3))

内容的提问来源于stack exchange，提问作者kei