将名称与嵌套列表相关联

Question

I'm stuck on how I can append additional information to the lowest level of a list leaf. I'm currently using:

fruits = ['tomato', 'apple', 'watermelon']

fruit_detail = []

for fruit in fruits:
    fruit_detail.append([[fruit, [fruit + ' is delicious']]])

Which gives me:

[[['tomato', ['tomato is delicious']]], [['apple', ['apple is delicious']]], [['watermelon', ['watermelon is delicious']]]]

Later on, I'm attempting to append more details to the list:

fruit_detail[tomato].append('red')

And I receive the error

NameError: name 'tomato' is not defined

Is it possible to achieve what I'm trying?

Answer 1

You should use a dictionary instead:

fruit_detail = {}

for fruit in fruits:
    fruit_detail[fruit] = [fruit + ' is delicious']

Now you can address each list by the fruit name:

>>> fruits = ['tomato', 'apple', 'watermelon']
>>> fruit_detail = {}
>>> for fruit in fruits:
...     fruit_detail[fruit] = [fruit + ' is delicious']
... 
>>> fruit_detail['tomato']
['tomato is delicious']
>>> fruit_detail['tomato'].append('red')
>>> fruit_detail['tomato']
['tomato is delicious', 'red']

Your code was using unnecessary extra lists, but to do the same with just a simple list:

fruit_detail = []

for fruit in fruits:
    fruit_detail.append([fruit, [fruit + ' is delicious']])

you'd have to scan through the whole list first to even find the matching list:

for fruit_name, fruit_info in fruit_detail:
    if fruit_name == 'tomato':
        fruit_info.append('red')

which is not nearly as efficient or easy to work with. The more items you add, the longer it takes to search. Dictionaries on the other hand are much, much more efficient in finding values you associated with a key.

For more information, see the Dictionaries section of the Python tutorial .