FAQ: Collections - Counter

This community-built FAQ covers the “Counter” exercise from the lesson “Collections”.

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This exercise can be found in the following Codecademy content:

Learn Intermediate Python 3

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I went to the last exercise and it didn’t pass. Here is the code:

opening_inventory = ['shoes', 'shoes', 'skirt', 'jeans', 'blouse', 'shoes', 't-shirt', 'dress', 'jeans', 'blouse', 'skirt', 'skirt', 'shorts', 'jeans', 'dress', 't-shirt', 'dress', 'blouse', 't-shirt', 'dress', 'dress', 'dress', 'jeans', 'dress', 'blouse']

closing_inventory = ['shoes', 'skirt', 'jeans', 'blouse', 'dress', 'skirt', 'shorts', 'jeans', 'dress', 'dress', 'jeans', 'dress', 'blouse']

# Write your code below!
from collections import Counter

def find_amount_sold(opening, closing, item):
  opening_count = Counter(opening)
  closing_count = Counter(closing)
  return opening_count[item]

tshirts_sold = find_amount_sold(opening_inventory, closing_inventory, "t-shirt")

I knew that there was nothing wrong. I tried to switch the "t-shirt" with 't-shirt' and it passed. How did Codecademy check that I used single quotes? It must be because it didn’t let me pass with double quotes. It might not be checking for equality because in Python "t-shirt" and 't-shirt' are equal. How do you check if a string is in single quotes and double quotes? Do most Python Learning Platforms suggest using double quotes or single quotes? Maybe I should get used to using single quotes also because I’m so used to double quotes.

Python translates double quotes to single quotes. It’s not an issue which we prefer to use. The occasional SCT might be matching literal expressions and not have a pattern match for the variations.


Such is the case in an environment with hundreds of authors and virtually nothing for a style guide. They write according to their individual styles and comprehension level. That leads to the diverse lesson checks that are the one irritant most common. It’s a MOOC, warts and all. Make the most of it.

Normally this doesn’t happen, the exercises don’t care if you use single quotes or double quotes.

What do those acronyms mean?

Submission Correctness Test

Massive Open Online Course

The latter should be followed up for accuracy. It might be ‘online open’.

I understand MOOC which means that the course in a course that is open to many people and is online which means that a lot of people with different abilities contribute to this course. But I don’t quite understand the S in SCT.

When we click Save or Run in an exercise (in the LE) it invokes the Submission Correctness Test. Our code in the editor is the submission to be tested.

Sometimes I view the test files of exercises. Like in this exercise which is the last one of the lesson: https://www.codecademy.com/courses/learn-intermediate-python-3/lessons/collections-python/exercises/review-of-specialized-containers-python.
The _test.py file:


  if len(promoted_bundles) != 2:
    fail_tests("`promoted_bundles` did not have the correct number of elements. Expected 2 but got " + str(len(promoted_bundles)))

except NameError:
  fail_tests("`Did you create a `list` called `promoted_bundles`?")
  if round(promoted_bundles[0].bundle_price, 2) != 106.95:
    fail_tests("`promoted_bundles` did not contain the correct data. Make sure that the sum of each bundle is calculated correctly and that only bundles with a price of over 100 dollars are included.")
  if round(promoted_bundles[1].bundle_price, 2) != 103.95:
    fail_tests("`promoted_bundles` did not contain the correct data. Make sure that the sum of each bundle is calculated correctly and that only bundles with a price of over 100 dollars are included.")

except NameError:
  fail_tests("Did you create a `list` called `promoted_bundles`?")

Where is load_file_in_context(), pass_tests() and fail_tests() defined?

Is the _test.py file a protected file like in a encapsulation exercise in the course? It taught me that to signal to other people that an attribute is protected you use one _ before the attribute.

An underscore in the name implies that the attribute is only ever accessed from a method.

What attribute? :thinking: :thinking: :thinking:

The one with the underscore in the name.

That’s the _test.py file, that’s not an attribute in the the _test.py file.

So the lesson allowed single quotes instead of double quotes thus Python didn’t recognize the difference between single quotes and double?

These last exercises are a nightmare for learners. The directions are unclear and badly written.