In python create a list with a variable in the name

Question

I'm trying to generate a series of (empty) lists using a for loop in python, and I want the name of the list to include a variable. e.g. y0, y1, y2 etc. Ideally looking something like this:

for a in range (0,16777216):
global y(a)=[]

Solution 1

why wouldn't you do a dictionary of lists?

y = {}
for a in range (0,16777216):
    y[a] = []

also for brevity: https://stackoverflow.com/a/1747827/884453

y = {a : [] for a in range(0,16777216)}

Solution 2

Not sure if this is quite what you want but couldn't you emulate the same behavior by simply creating a list of lists? So your_list[0] would correspond to y0.

Solution 3

The answer is: don't. Instead create a list so that you access the variables with y[0], y[1], etc. See the accepted answer here for info.

Solution 4

Maybe you should check out defaultdict

form collection import defaultdict

# This will lazily create lists on demand
y = defaultdict(list)

Also if you want a constraint on the key override the default __getitem__ function like the following...

def __getitem__(self, item):
    if isintance(item, int) and 0 < item < 16777216:
         return defaultdict.__getitem__(self, item)
    else:
         raise KeyError

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Comments

[kojiro]

Except all the keys are integers, so perhaps a list of lists or sparse array?

[Francis Yaconiello]

i typo'd that a, it wasn't supposed to be a string. fixed.

[Burhan Khalid]

You should mark this question as a duplicate to the one you linked.

[Francis Yaconiello]

added dict comprehension