Extract all keys from a list of dictionaries

Question

I\'m trying to get a list of all keys in a list of dictionaries in order to fill out the fieldnames argument for csv.DictWriter.

previously, I had something like thi

Answer 1

from itertools import chain

lis = [
    {"name": "Tom", "age": 10},
    {"name": "Mark", "age": 5, "height":4},
    {"name": "Pam", "age": 7, "weight":90}
]

# without qualification a dict iterates over its keys
# and set takes any iterable in its constructor
headers_as_set = set(chain.from_iterable(lis))

# you asked for a list
headers = list(
    set(chain.from_iterable(lis))
)