yamledit.py

import yaml


class YamlEdit:
    def __init__(self, filename):
        self.filename = filename

    def __enter__(self):
        with open(self.filename) as f:
            self.yaml_obj = yaml.safe_load(f)
        return self.yaml_obj

    def __exit__(self, exc_type, exc_val, exc_tb):
        with open(self.filename, "w") as f:
            yaml.dump(self.yaml_obj, f, default_flow_style=False)

if __name__ == "__main__":
    with YamlEdit("file.yaml") as y:
        y["foo"] = "bar"