Intro to Python: Day 19 - Building a Dictionary

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Dictionaries are an essential building block in programming and a fundamental data type in most languages. In Python, we can build a dictionary simply by declaring an empty one.

state_population_dict = {}

We can then add to it by explicitly naming a key-value pair. Here we are adding states to our state_population_dict dictionary with their respective populations:

state_population_dict["WA"] = 7739000
state_population_dict["NY"] = 19840000

We can then check the value of a key in the dictionary simply by calling the dictionary with the key in brackets.

print(state_population_dict["WA"])
# prints 7739000

If we try to check the value of a key that does not exist on the dictionary, we will get a KeyError which states the key does not exist on the dictionary.

To check if a key exists on the dictionary before requesting to get its value, we can use the in keyword.

if ("TX" in state_population_dict):
    print(state_population_dict["TX"])
else:
    print("TX population not in dictionary")

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