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Chapter 4: Dictionaries

Retrieving from dictionaries

face Josiah Wang

As you would expect, you can retrieve the value of a dict given a key.

>>> student_dict = {"00-01-30": "Ali", "00-02-11": "Simon", 
...                 "00-05-67": "Francesca", "00-09-88": "Cho"
...                }
>>> best_student = student_dict["00-02-11"]
>>> print(best_student)
Simon

But what if the key cannot be found? What happens? (Try this!)

>>> student_dict["00-11-22"]    # What error message do you get? 

So you should check whether the key exists before trying to use the key to retrieve a value.

>>> if "00-11-22" in student_dict:
...    active_student = student_dict["00-11-22"]
...
>>> 

Alternatively, you can use dict‘s get() method to retrieve a value. You can conveniently assign a default value if the key does not exist.

>>> real_student = student_dict.get("00-09-88", "John Doe")
>>> print(real_student)
Cho
>>> imaginary_student = student_dict.get("11-22-33", "John Doe")
>>> print(imaginary_student)
John Doe