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Python Technical Interview Prep: Python Basics Basic Python Down The Rabbit Hole

Noor Hafiza Binti Ibrahim
Noor Hafiza Binti Ibrahim
11,712 Points
Posted by Noor Hafiza Binti Ibrahim
Noor Hafiza Binti Ibrahim
11,712 Points

i'm absolutely lost on this one. how do i use the filter lambda() here? another solution?

Bummer: TypeError: filter expected 2 arguments, got 1

nested.py 
# {
#     'name': 'Javier Hernandez',
#     'pets': [
#         {
#             'name': 'Kitty',
#             'breed': 'American Shorthair'
#         },
#         {
#             'name': 'Buzz',
#             'breed': 'Pitbull'
#         }
#     ],
#     'classes': ('Math', 'Science', 'Art')
# }
# enter your code below
def breeds(data):
    return list(filter(lambda item: item.get('breed')))

1 Answer

Chris Freeman
MOD
Chris Freeman
Treehouse Moderator 68,457 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,457 Points

Hey Noor Hafiza Binti Ibrahim, That's a really neat question. I haven't see a solution using filter, so let's dig into it!

Let's fix the first error. The builtin filter function takes two arguments, the second (missing) argument is the iterable object.

Let's try data:

    filter(lambda item: item.get('breed'), data)

If we use the data object passed in, it will fail because. using data in a interable context will just return the keys of the dictionary. This causes an error because the first key "name" is a string which does not have the get() method:

AttributeError: 'str' object has no attribute 'get'

Let's go deeper and try the list found at data["pets"]

    filter(lambda item: item.get('breed'), data["pets"]))

This also fails since filter is simply looking for a "true" result. Since "breed" is a valid key to each dictionary in data["pets"], the entire dictionary is returned. This is equivalent to:

for item in data["pets"]:
    if item.get('breed'):
        print(item)  # entire item

# results:
# {'name': 'Kitty', 'breed': 'American Shorthair'}
# {'name': 'Buzz', 'breed': 'Pitbull'}

What will work is to use map instead of filter. This will return the result of the lambda and not the whole object.

    map(lambda item: item.get('breed'), data["pets"]))

This works because it returns the result of each get. This is equivalent to:

for item in data["pets"]:
    if item.get('breed'):
        print(item.get('breed')) # the breed value


# results:
American Shorthair
Pitbull

Post back if you need more help. Good luck!!