Python方式遍历对象属性并分配新属性

Question

I am working with a large object a in Python. The object has two other iterable objects b and c passed to it as attributes one and two .

I want to consolidate the important data in the object prior to passing it to the templating engine. I am trying to take an attribute from one and assign it to two .

My first thought was to parse the two objects with two stacked for loops like this..

for c in a.two:
    for a in a.one:
        if a.id == c.id:
            setattr(c, 'title', a.title)

However, I am not sure if this is the most pythonic way of doing this.

Answer 1

You can improve your code from a time complexity of O(nxm) to O(n + m) (quadratic to linear) by building a dict for each list that maps the id s of objects in the list to the objects, and using set intersection between the dict keys to find the common id s between the two lists instead. Also, you don't need to use the setattr function if the attribute name you're setting is fixed; you can assign to the object's attribute directly instead:

one = {obj.id: obj for obj in a.one}
two = {obj.id: obj for obj in a.two}
for id in set(one).intersection(two):
    two[id].title = one[id].title