pyyaml-include

abc.yaml

a: 1
b: 2

load.py

import yaml

def include_constructor(loader, node):
    """Include content at node."""
    v = open(node.value).read()
    return yaml.load(v, Loader=loader.__class__)

yaml.add_constructor("!include", include_constructor, Loader=yaml.SafeLoader)
string = """
x: &x !include "abc.yaml"
y: *x
"""
data = yaml.safe_load(string)
print(data)

output.txt

{'x': {'a': 1, 'b': 2}, 'y': {'a': 1, 'b': 2}}