what does 'in' do for dictionaries in python code example

Example: python make a dictionary

#title			: Dictionary Example
#author         : Joyiscold
#date           : 2020-02-01
#====================================================

thisdict = {
	"brand": "Ford",
 	"model": "Mustang",
 	"year": 1964
}

#Assigning a value
thisdict["year"] = 2018