Why variable replacement does not work in Python nested loop

Question

I have the following code:


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)

The task I want to achieve is this:

Within the range(3) loop, loop through mylist.
When the content of my list exist in threshold_dict_by_patient_and_visit dictionary (in this case k2-01-003|15) replace the lower_threshold and upper_threshold with the value in that dictionary. Otherwise use default value: 6.33 and 1e+30

The result I expect is this:

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

Why it gives this instead:

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

What's the right way to go about it?

I'm using Python 3.8.5.

Update

I tried to add else but still doesn't work:

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)

Add an else where you reset to the default values for the threshold variables? — Some programmer dude
– Some programmer dude, Commented Oct 19, 2020 at 7:39
@Someprogrammerdude I tried. It doesn't work. see my update above. — littleworth
– littleworth, Commented Oct 19, 2020 at 7:40
With lower_threshold, upper_threshold = lower_threshold, upper_threshold you just assign the same values as the variables already have. You need to assign the default value, explicitly. — Some programmer dude
– Some programmer dude, Commented Oct 19, 2020 at 7:42

Jasmijn · Accepted Answer · 2020-10-19 07:42:55Z

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)

answered Oct 19, 2020 at 7:42

Jasmijn

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Glatinis · Accepted Answer · 2020-10-19 07:44:30Z

0

Here is a clean and working solution:

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)

answered Oct 19, 2020 at 7:44

Glatinis

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