Python Introducing Dictionaries Iterating and Packing with Dictionaries Iterate over Dictionaries

Why does the beginning of Ashley's "for" loop end with "course.items():" as opposed to just "course:" ?

Here is the code:

course = {'teacher':'Ashley', 'title':'Introducing Dictionaries', 'level':'Beginner'}

for key, value in course.items(): 
    print(key, value)

What is the reason the code needs to be course.items(): instead of course:? Thanks in advance 😁

1 Answer

Jeff Muday
MOD
Jeff Muday
Treehouse Moderator 26,279 Points

Good question-- at first dictionaries don't seem like something you would use much, but they are an amazing way to structure data!

To answer your question: You want to use course.items() is because course is a dictionary. If you iterate through a dictionary, 99 % of the time you will want both the KEY and the VALUE from the course dictionary iterable.

But there are ways to just loop through the keys or just the values... see below.

Python 3.6.9 (default, Nov  7 2019, 10:44:02)
[GCC 8.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> course = {'teacher':'Ashley', 'title':'Introducing Dictionaries', 'level':'Beginner'}
>>>
>>> for key, value in course.items():
...     print(key, value)
...
teacher Ashley
title Introducing Dictionaries
level Beginner

If we only loop through course, we will get a syntax error:

>>> for key, value in course:
...     print(key, value)
...
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: too many values to unpack (expected 2)

We can loop through just the keys like this:

>>> for key in course:
...     print(key)
...
teacher
title
level

We can also loop through the keys this way:

>>> for key in course.keys():
...     print(key)
...
teacher
title
level

We can also loop through ONLY the values like this:

>>> for value in course.values():
...     print(value)
...
Ashley
Introducing Dictionaries
Beginner

Great, thanks for the in depth explanation Jeff! Much appreciated 😁