Arrays/dictionaries in python

I was trying to create a method that does a loop and in the process it creates array with 2 levels.

In PHP it would look like this

for($a = 0; $a < 3; $a++) {
    $something[$a] = [1,2,3];
}

But the problem is with python. I can't seem to add the key "u" to the variable and the array under it in the same time. How would you do this properly?

My current code:

for u in range(3):
    something[u] = [1,2,3] #this line doesn't seem to work
    somethingElse = [1,2,3] #开发者_如何学运维this works properly

Please excuse me if this is a stupid question. I am a beginner and I already tried googling it, but didn't actually find anything useful.

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The best way to find information that you need is to use python tutorial. For example to answer your question yourself you can take a look at the following link: http://docs.python.org/tutorial/datastructures.html

You can use list comprehension:

something = [[1,2,3] for u in xrange(3)]

OR map:

something = map(lambda x: [1,2,3], xrange(3))

OR insert(if you need to insert into the exact index) or append to add item to the end of list:

something = [[1,2,3]]
something.append([1,2,3])# something == [[1,2,3],[1,2,3]]
something.insert(0, [2,3,1])# something == [[2,3,4],[1,2,3],[1,2,3]]

If you would like to use mappings(dictionary):

something = {}
for u in xrange(3):
   something[u] = [1,2,3]

---

It's easier when you forget all about PHP. You need to create an empty list first.

something = []
for u in range(3):
    something.append([1, 2, 3])

Note that something[u] won't work, because there is no u-th element in the list. Don't confuse lists (or arrays) with mappings.

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You can't use an index within a list that doesn't exist.

something = []
for u in range(3):
    something.append([1, 2, 3])

---

You haven't populated that initial list yet.

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It seems like what you actually want may be a dictionary, not a list.

something = {}
for u in range(3):
    something[u] = [1,2,3]

With a list, the list has to already have at least u elements before you can assign list[u], but with a dictionary you can add new items arbitrarily.