Python：如何在if语句中使用类型函数？

Question

我正在编写一个从文件加载数据列表的程序，我需要该程序区分行中的数据是字符串还是整数。 但是，在我完成的代码中，程序无法区分数字和字符串。

我拥有的数据列表示例：

HAJOS
ALFRED
1896
1

我的代码：

def medalsYear():
  times = 1
  totalGold = 0
  totalSilver = 0
  totalBronze = 0
  while times <= 5:
    alpha = fob.readline() #reads file line by line#
    print(alpha)
    times = times + 1
    if type(alpha) == int:
        if alpha == 1:
            totalGold = totalGold + 1
            print("gold medal won")
        elif alpha == 2:
            totalSilver = totalSilver + 1
            print("silver medal won")
        elif alpha == 3:
            totalBronze = totalBronze + 1
            print("bronze medal won")
        else:
            pass
    else:
        print('is a string')
  print(totalGold, "Gold medals won")
  print(totalSilver, "Silver medals won")
  print(totalBronze, "Bronze medals won")

我的问题是，当程序读取包含整数的行时，它无法正确确定该行是否包含整数，并从那里开始执行相应的if语句。 目前，我的输出如下所示。

HAJOS
is a string
ALFRED
is a string
1896
is a string
1
is a string

is a string
0 Gold medals won
0 Silver medals won
0 Bronze medals won
done

Answer 1

从文件读取的数据将始终是字符串。 您需要尝试转换这些行，而不是测试它们的类型：

try:
    alpha = int(alpha)
    if alpha == 1:
        totalGold = totalGold + 1
        print("gold medal won")
    elif alpha == 2:
        totalSilver = totalSilver + 1
        print("silver medal won")
    elif alpha == 3:
        totalBronze = totalBronze + 1
        print("bronze medal won")
except ValueError:
    print('is a string')

当alpha无法解释为整数时， int()将引发ValueError 。 如果引发此异常，则会导致Python跳至except ValueError:块except ValueError:块，而不是执行try:套件的其余部分。

Answer 2

您可以创建一个dict，其中键为"1","2" and "3"以对应于金，银，青铜，然后使用dict.get。

with open(infile) as f:
    times = 1
    medal_dict = {"1": 0, "2": 0, "3": 0}
    while times <= 5:
        alpha = f.readline().rstrip()  #reads file line by line#
        times += 1
        if medal_dict.get(alpha) is not None:
            medal_dict[alpha] += 1
        else:
            print("is a string")
    print(medal_dict["1"], "Gold medals won")
    print(medal_dict["2"], "Silver medals won")
    print(medal_dict["3"], "Bronze medals won")

哪个输出：

(1, 'Gold medals won')
(0, 'Silver medals won')
(0, 'Bronze medals won')

如果要在循环中赢得奖牌时打印：

with open(infile) as f:
    times = 1
    medal_dict = {"1": [0,"gold"], "2": [0,"silver"], "3": [0,"bronze"]}
    while times <= 5:
        alpha = f.readline().rstrip()  #reads file line by line#
        print(alpha)
        times += 1#
        check = medal_dict.get(alpha)
        if check is not None:
            medal_dict[alpha][0] += 1
            print("{} medal won".format(check[1]))
        else:
            print("is a string")
    print(medal_dict["1"][0], "Gold medals won")
    print(medal_dict["2"][0], "Silver medals won")
    print(medal_dict["3"][0], "Bronze medals won")