I want to find all 5-digit strings, for which

• the first three digits are in my first list,
• the second trough fourth are in my second and
• the third to fifth are in my last list:

l0=["123","567","451"]
l1=["234","239","881"]
l2=["348","551","399"]

should thus yield: ['12348', '12399'].

I have therefore written a funciton is_successor(a,b) that tests if a and b overlap:

def is_successor(a:str,b:str)->bool:
    """tests if strings a and b overlap"""
    return a[1:]==b[:2]

I can then achieve my goal by writing this nested loop/check structure, that basically appends back to front strings and resulting in all valid strings:

pres=[]
for c in l2:
    for b in l1:
        if is_successor(b,c):
            for a in l0:
                if is_successor(a,b):
                    pres.append(a[0]+b[0]+c)

pres

• I know I could write it as a list comprehension, but for my original data i have more nested lists and i loose readability even in a list comprehension.
• I start from l2 -> l0 because in my original data the lists become longer, the lower the index and thus I can filter out more cases early this way.
• A single loop trough all combinations of l0,l1,l2 and checking the succession of all items a,b,c simultaneously would work but it test way more unnecessary combinations than my current construct does.

Question:

How can this nested loop and conditional checking call be astracted? Is there a pythonic way to capture the repetition of for -> is_successor()?