Create a function that takes a string containing integers as well as other characters and return the sum of the negative integers only.

Sure, here is a Python function that does exactly that:

import re

def sum_of_negatives(s):
    # Use regex to find all negative integers in the string
    negatives = re.findall(r'-\d+', s)
    # Convert the strings to integers and sum them
    return sum(int(i) for i in negatives)

This function works by first using a regular expression to find all instances of negative integers in the input string. The regular expression -\d+ matches a hyphen followed by one or more digits. The findall function returns a list of all matches as strings.

Then, it uses a generator expression to convert each string in the list to an integer and sum them. The sum function returns the sum of all numbers in an iterable.

You can use this function like this:

s = "abc-123def-456ghi789"
print(sum_of_negatives(s))  # Outputs: -579

This will find the negative integers -123 and -456 in the string and return their sum, -579.