flatten_arbitrary_inner_arrays.py

def main():
    from sys import stdin
    from ast import literal_eval
    
    def flatten(l):
        i = 0
        nao_muda = False
        while i<len(l):
            nao_muda = False
            try:
                if isinstance(l[i],list):
                    l.extend(l[i])
                    del l[i] 
                    nao_muda = True                
            except TypeError:
                pass
            if not nao_muda: i+=1
        return l
    
    def innerList(l,r=[]):
        for e in l:
            try:
                if isinstance(e,list):
                    r = flatten(e)
                    l.remove(e)
                    return innerList(l,r)                
            except TypeError:
                r.append(e)
                continue   
        l.extend(r)         
        return sorted(l)
    a = literal_eval(stdin.readline())
    
    print(innerList(a))

if __name__=='__main__':
    main()

This implementation is for:
Write some code, that will flatten an array of arbitrarily nested arrays of integers into a flat array of integers. e.g. [[1,2,[3]],4] -> [1,2,3,4].