Python update a key in dict if it doesn't exist

Question

I want to insert a key-value pair into dict if key not in dict.keys(). Basically I could do it with:

if key not in d.keys():
    d[key] = value

Answer 1

With the following you can insert multiple values and also have default values but you're creating a new dictionary.

d = {**{ key: value }, **default_values}

I've tested it with the most voted answer and on average this is faster as it can be seen in the following example, .

Speed test comparing a for loop based method with a dict comprehension with unpack operator method.

if no copy (d = default_vals.copy()) is made on the first case then the most voted answer would be faster once we reach orders of magnitude of 10**5 and greater. Memory footprint of both methods are the same.