Nested Lists & Dictionaries

[Hudjefa]

So I'm learning about nested dictionaries and loops.
I wrote the following short program:

a_morning = {"Sara": ["dressed", "breakfasted"], 
             "Alex": ["breakfasted", "dressed"]}

for name in a_morning:
        print(name + " " + a_morning[name][0] + " and " + a_morning[name][1])

The lesson talks about how lists can keep track of sequence or order . The code piece above shows how Alex and Sara begin their morning. I use a dictionary and inside it I nest a list.

Is the format for the for loop the only one I can apply to a dictionary? I can't seem to use a numerical/integer index (returns an error I think) like:

for i in range(len(a_morning))

[menator01]

When working with dicts I prefer doing one of the following. There are other ways.
Dicts work with key, value pairs

a_morning = {"Sara": ["dressed", "breakfasted"], 
             "Alex": ["breakfasted", "dressed"]}

for key, val in a_morning.items():
    print(key , ', '.join(val))
    print(key , val[0])
    print(key , val[1])
    print()

Output:
Sara dressed, breakfasted
Sara dressed
Sara breakfasted

Alex breakfasted, dressed
Alex breakfasted
Alex dressed

[ndc85430]

Dictionaries don't support indexing; you only access their values by key. So, it doesn't make sense what you're trying to do.

[Pedroski55]

You may certainly use integers as the names of the array keys, and almost anything as the value under that name.

Nesting can be complex. You may lose the track of what is where.

madrugada = {1:{"who": "Sara", "what": ["dressed", "breakfasted"]},
             2: {"who": "Alex", "what": ["breakfasted", "dressed"]}}

madrugada[1]

Output:
{'who': 'Sara', 'what': ['dressed', 'breakfasted']}

[python]madrugada[2][/python]
             
{'who': 'Alex', 'what': ['breakfasted', 'dressed']}

for key in madrugada.keys():
             print(key, madrugada[key])

Output:
1 {'who': 'Sara', 'what': ['dressed', 'breakfasted']}
2 {'who': 'Alex', 'what': ['breakfasted', 'dressed']}

madrugada[1]["who"]

Output:
'Sara'

madrugada[1]["what"]

Output:
['dressed', 'breakfasted']

[deanhystad]

Since python 3.6 the only real difference between dictionaries and lists is that index keys for lists have to be int while dictionary keys only have to be hashable. Prior to 3.6, dictionaries were unordered. You could iterate through a dictionary, but the order of items was unpredictable.

Unless a dictionary is huge, it is easy to index a dictionary as you would a list, by position. All you need is a list of the dictionary keys.

a_morning = {
    "Sara": ["dressed", "breakfasted"], 
    "Alex": ["breakfasted", "dressed"]
}
names = list(a_morning)  # makes list of dictionary keys
name = names[0]
print(name + " " + a_morning[name][0] + " and " + a_morning[name][1])

If you only want to know the "first" item in a dictionary it is safer to use an iterator. This works quickly for small or giant dictionaries.

a_morning = {
    "Sara": ["dressed", "breakfasted"], 
    "Alex": ["breakfasted", "dressed"]
}

name = next(iter(a_morning))
print(name + " " + a_morning[name][0] + " and " + a_morning[name][1])

But you really shouldn't ever care about the order of items in a dictionary. If you want something that acts like a list, make a list. If you want something that acts like a dictionary, make a dictionary.

[DeaD_EyE]

The name as key for a "database" is a problem, if you have two or more persons with the same name.

You could use an easier data structure:

a_morning = [
    ["Sara", "dressed", "breakfasted"],
    ["Alex", "breakfasted", "dressed"],
]

name, word1, word2 = a_morning[0]

With star-assignment.

a_morning = [
    ["Sara", "dressed", "breakfasted"],
    ["Alex", "breakfasted", "dressed"],
]

name, *words = a_morning[0]
# name is the first element of a_morning[0]
# words is a list with variable length

Or you put dicts in a list:

a_morning = [
    {"name": "Sara", "color": "red"},
    {"name": "Alex", "color": "blue"},
]

player0 = a_morning[0]

Iterating over the list by filtering by name:

a_morning = [
    {"name": "Sara", "color": "red"},
    {"name": "Alex", "color": "blue"},
]


only_saras = []
for player in a_morning:
    if player.get("name", "").lower() == "sara":
        only_saras.append(player)