You want to traverse the dictionary, building the current key and accumulating the flat dictionary. For example:
def flatten(current, key, result):
    if isinstance(current, dict):
        for k in current:
            new_key = "{0}.{1}".format(key, k) if len(key) > 0 else k
            flatten(current[k], new_key, result)
    else:
        result[key] = current
    return result
result = flatten(my_dict, '', {})
Using it:
print(flatten(_dict1, '', {}))
{'this.example.too': 3, 'example': 'fish', 'this.is.another.value': 4, 'this.is.an.example': 2}
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solved How to flatten a nested dictionary? [duplicate]