您可以尝试使用多个if条件来检查特定列中的值：

col = ['q1', 'q2', 'q3', 'q4']

for i in col:
    count = 0
    if 'a' in df[i].unique():
        count += df[i].value_counts()['a']
    if 'b' in df[i].unique():
        count += df[i].value_counts()['b']
    if 'c' in df[i].unique():
        count += df[i].value_counts()['c']
    if 'd' in df[i].unique():
        count += df[i].value_counts()['d']
    print(count)

您可以尝试在for（）中声明这些值：

col = ['q1', 'q2', 'q3', 'q4']
values = ['a', 'b', 'c', 'd']
for i in col:
    count = 0
    for v in values:
        if v in df[i].values:
            count += df[i].value_counts()[v]
    print(count)

您可以使用、创建列表和附加：

list_C = []
for i in cols:
    a = df[i].str.count("A").sum()
    list_C.append(a)
    b = df[i].str.count("B").sum()
    list_C.append(b)
    c = df[i].str.count("C").sum()
    list_C.append(c)
    d = df[i].str.count("D").sum()
    list_C.append(d)

print(list_C)
print(sum(list_C))