为什么变量替换在 Python 嵌套循环中不起作用

Question

我有以下代码：

lower_threshold = 6.33
upper_threshold = 1e+30
threshold_dict_by_patient_and_visit = {
    "k2-01-003|15" : [15.007, 1e+30]
}
mylist = ['k2-01-003|18', 'k2-01-003|13','k2-01-003|15']

for i in range(3):
    for patient_visit in mylist:
        if (patient_visit in threshold_dict_by_patient_and_visit):
            lower_threshold, upper_threshold = threshold_dict_by_patient_and_visit[patient_visit]
        print(i, patient_visit, lower_threshold, upper_threshold)

我要完成的任务是这样的：

1. 在range(3)循环中，循环遍历mylist 。
2. 当我的列表内容存在于threshold_dict_by_patient_and_visit字典（在本例中为k2-01-003|15 ）时，用该字典中的值替换lower_threshold和upper_threshold 。 否则使用默认值： 6.33和1e+30

我期望的结果是这样的：

0 k2-01-003|18 6.33 1e+30
0 k2-01-003|13 6.33 1e+30
0 k2-01-003|15 15.007 1e+30
1 k2-01-003|18 6.33 1e+30
1 k2-01-003|13 6.33 1e+30
1 k2-01-003|15 15.007 1e+30
2 k2-01-003|18 6.33 1e+30
2 k2-01-003|13 6.33 1e+30
2 k2-01-003|15 15.007 1e+30

为什么它会给出这个：

0 k2-01-003|18 6.33 1e+30
0 k2-01-003|13 6.33 1e+30
0 k2-01-003|15 15.007 1e+30
1 k2-01-003|18 15.007 1e+30
1 k2-01-003|13 15.007 1e+30
1 k2-01-003|15 15.007 1e+30
2 k2-01-003|18 15.007 1e+30
2 k2-01-003|13 15.007 1e+30
2 k2-01-003|15 15.007 1e+30

正确的做法是什么？

我正在使用 Python 3.8.5。

---

更新

我尝试添加else但仍然不起作用：

for i in range(3):
    for patient_visit in mylist:
        if (patient_visit in threshold_dict_by_patient_and_visit):
            lower_threshold, upper_threshold = threshold_dict_by_patient_and_visit[patient_visit]
        else:
            lower_threshold, upper_threshold = lower_threshold, upper_threshold
        print(i, patient_visit, lower_threshold, upper_threshold)

Answer 1

threshold_dict_by_patient_and_visit = {
    "k2-01-003|15" : (15.007, 1e+30) # using tuple instead of list because you don't need to mutate them; this is not mandatory
}
default_thresholds = (6.33, 1e+30)
mylist = ['k2-01-003|18', 'k2-01-003|13','k2-01-003|15']

for i in range(3):
    for patient_visit in mylist:
        #dict.get: get an item if it exists, otherwise return a default value
        lower_threshold, upper_threshold = threshold_dict_by_patient_and_visit.get(patient_visit, default_thresholds)
        print(i, patient_visit, lower_threshold, upper_threshold)

Answer 2

这是一个干净且有效的解决方案：

threshold_dict_by_patient_and_visit = {
    "k2-01-003|15" : [15.007, 1e+30]
}
mylist = ['k2-01-003|18', 'k2-01-003|13','k2-01-003|15']

for i in range(3):
    lower_threshold = 6.33
    upper_threshold = 1e+30
    
    for patient_visit in mylist:
        if patient_visit in list(threshold_dict_by_patient_and_visit.keys()):
            lower_threshold, upper_threshold = threshold_dict_by_patient_and_visit[patient_visit]
        print(i, patient_visit, lower_threshold, upper_threshold)