unexpected behavior with vim built-in completion used

[vitmy0000]

I have the following code which should follow the PEP8 guideline.

word = 'hello'
foo = long_function_name_oooooooooooooooooooooooooooooooooooooooooooooooooooo(
    var_one, var_two)

A very common scenario is that I want to append one more argument to the argument list.
And I'm trying to use vim built-in completion feature.
Here I'm using the command C-n to complete the variable name.

After I hit <CR>, the code goes to this. This is definitely not what I expect.

[vitmy0000]

I just found that this is caused by the conflict with "auto-pairs"