Use different dictionary in separate for-loops

Question

I want my for loop to change the variable if there is a KeyError,

numlist1 = {"one": 1}

numlist2 = {"two": 3}

numlist3 = {"three": 3}

userinputfix = ["two", "five"]

newlist = []
for x in userinputfix:
    newlist.append(numlist1[x])

So if there is no "two" in numlist1, it should repeat the loop replacing numlist1 with numlist2, numlist3,...

I tried to use handling exceptions method:

numlist1 = {"one": 1}

numlist2 = {"two": 3}

numlist3 = {"three": 3}

userinputfix = ["two", "five"]

y = 1
newlist = []
for x in userinputfix:
    try:
        newlist.append(numlist{y}[x])
    except KeyError:
        y += 1

Something like the above but my code is not correct.

Does this answer your question? [What is the purpose of collections.ChainMap?](https://stackoverflow.com/questions/23392976/what-is-the-purpose-of-collections-chainmap) — Mechanic Pig, Dec 30 '22 at 15:22
You should NOT rely on variable names like that. You could use `walrus` operator and some hacky code to achieve that, but it's just a bad approach. You should group your `numlistX` stuff into another data structure and use regular looping for your usecase... — Gameplay, Dec 30 '22 at 15:24

score 0 · Answer 1 · answered Dec 30 '22 at 15:29

So, I 'think' you want to produce an output of [2] for the above? I.e. taking a list of matching values from each of the lists ignoring those that don't have a matching key?

You can't access 'numlist2' by using 'numlist{2}' as you're attempting there. If there is a short, fixed number of lists, you need to iterate them specifically:

newlist = []
for x in userinputfix:
    for d in (numlist1, numlist2, numlist3):
        try:
            newlist.append(d[x])
        except KeyError:
            pass

If you want to use any dictionary that starts "numbest", then it'll be something horrible like...

dicts = [globals()[x] for x in globals() if x.startswith("numlist") and type(globals()[x]) == dict]
newlist = []
for x in userinputfix:
    for d in dicts:
        try:
            newlist.append(d[x])
        except KeyError:
            pass

This makes a list of all global variables that start 'newlist' and are dictionaries, then those are iterated.

score -1 · Answer 2 · answered Dec 30 '22 at 19:22

Here is using dict.get and while loop with try except and eval

numlist1 = {"one": 1}
numlist2 = {"two": 3}
numlist3 = {"three": 3}
numlist4 = {"four": 4}

userinputfix = ["four", "two", "five", "one"]

newlist = []
i = 1
for x in userinputfix:
    while True:
        try:
            val = eval(f'numlist{i}').get(x)
            if val != None:
                newlist.append(val)
            i += 1
        except NameError:
            break
    i = 1

print(newlist)

# [4, 3, 1]

For each x in userinputfix, it will try to find x in every dictionaries variable by increasing i by 1 until it found NameError and resetting i back to 1 to continue to the next x. If the value is None or x not found, it'll not get appended to newlist.

Use different dictionary in separate for-loops

2 Answers2