[Python] How can I get a list of all nested keys from JSON?

My JSON:

{
"Name1": {
"NNum": "11",
"Node1": {
"SubNodeA": "Thomas",
"SubNodeB": "27"
},
"Node2": {
"SubNodeA": "ZZZ",
"SubNodeD": "XXX",
"SubNodeE": "yy"
},
"Node3": {
"child1": 11,
"child2": {
"grandchild": {
"greatgrandchild1": "Rita",
"greatgrandchild2": "US"
}
}
}
}
}


The format or keys are not defined and can go to any depth. I want a list of keys:

keyList= ["Name1.NNum","Name1.Node1.SubNodeA",""Name1.Node1.SubNodeB","Name1.Node2.SubNodeA","Name1.Node2.SubNodeD","Name1.Node2.SubNodeE","Name1.Node3.child1","Name1.Node3.child2.grandchild.greatgrandchild1","Name1.Node3.child2.grandchild.greatgrandchild2"]


My code:

def extract_values(obj):
"""Pull all values of specified key from nested JSON."""
arr = []
key_list = []
parent = ""
def extract(obj, arr,parent):
"""Recursively search for values of key in JSON tree."""
if isinstance(obj, dict):
grandparent = ""
for k, v in obj.items():
print ("k ............",k)
parent = grandparent
temp_parent = k
print ("parent >>>>> ",parent)

if isinstance(v, (dict, list)):
parent = temp_parent
print ("IF VALUE DICT .. parent ", parent)
extract(v, arr,parent)
else:
grandparent = parent
parent = parent + "_" + temp_parent
print ("!!!! NOT DICT .... **** parent ... ", parent)
arr.append(parent)

elif isinstance(obj, list):
for item in obj:
extract(item, arr)
#print ("arr >>>>>>>>>> ", arr)
time.sleep(5)
return arr

results = extract(obj, arr,parent)
return results


But this does not give the expected output.

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