Ugly JMESPath hack: How to access a parent property

.python-version

3.6.2

.venv

lambdascraper

fetchstore.py

import jmespath
from jmespath import functions


class CustomFunctions(functions.Functions):
    """
    JMESPath hack to retrieve the parent element if you need it.

    """


    def __init__(self,context=None):
        super().__init__()
        self.data={}


    @functions.signature({'types': ['string']},{'types': ['string']})
    def _func_store(self,s,var):
        """
            stores value s in the variable var. can later be retrieved using fetch
        """
        self.data[var]=s
        return s

    @functions.signature({'types': ['string']})
    def _func_fetch(self,var):
        """
            returns variable var or None
        """
        return self.data.get(var,None)


def test() :
    import json
    input=json.loads("""
        { "name" : "parent name",
        "data" : [
            { "x" : 1, "y" : 2 },
            { "x" : 3, "y" : 2 }
            ]
        }
    """)
    options = jmespath.Options(custom_functions=CustomFunctions())
    output = jmespath.search("{ name: store(name,'name'), data: data[][ fetch('name'),x, y] }",input,options=options)
    assert output==json.loads("""
			{
			 "name": "parent name",
			 "data": [
			   [ "parent name", 1, 2 ],
			   [ "parent name", 3, 2 ]
			 ]
			}
		""")


if __name__ == "__main__" :
          test()