any better code to initalize a list of lists?

[John]

For my code of radix sort, I need to initialize 256 buckets. My code looks a
little clumsy:

radix=[[]]
for i in range(255):
radix.append([])

any better code to initalize this list?

 

[Paul Rubin]

For my code of radix sort, I need to initialize 256 buckets. My code looks a
little clumsy:

radix=[[]]
for i in range(255):
radix.append([])

any better code to initalize this list?

Typically you'd say
radix = [[] for i in xrange(256)]

but what are you really doing? This plan to implement radix sorting
sounds a little bit odd, unless it's just an exercise.

You could also consider using a dictionary instead of a list,
something like:

radix = defaultdict(list)

 

[John]

I want to radix sort non-negative integers that can fit into 32-bits. That
will take 4 passes, one for each byte. So, I will need 256 "buckets"
The list radix of 256 elements of list is good for this purpose.

Your code is much shorter, works and probably takes less time.

Thanks!

John

For my code of radix sort, I need to initialize 256 buckets. My code
looks a
little clumsy:

radix=[[]]
for i in range(255):
radix.append([])

any better code to initalize this list?

Typically you'd say
radix = [[] for i in xrange(256)]

but what are you really doing? This plan to implement radix sorting
sounds a little bit odd, unless it's just an exercise.

You could also consider using a dictionary instead of a list,
something like:

radix = defaultdict(list)

 

[Paul Rubin]

I want to radix sort non-negative integers that can fit into 32-bits.

But why do you want to do that? Why not just use Python's built-in
sorting operation?

 

[Terry Reedy]

| > I want to radix sort non-negative integers that can fit into 32-bits.
|
| But why do you want to do that? Why not just use Python's built-in
| sorting operation?

Perhaps to learn or teach about the algorithm. Python is good for that.

 

[Donald Fredkin]

For my code of radix sort, I need to initialize 256 buckets. My code
looks a little clumsy:

radix=[[]]
for i in range(255):
radix.append([])

any better code to initalize this list?

radix = [[[]]*256][0]

--

 

[Stargaming]

John wrote:

For my code of radix sort, I need to initialize 256 buckets. My code
looks a little clumsy:

radix=[[]]
for i in range(255):
radix.append([])

any better code to initalize this list?

radix = [[[]]*256][0]

>>> x = [[[]]*256][0]
>>> x

[[], [], [], [], [], [], [], [], [], [], [], [], [], [], [], [], [], [],
[], [], ...

>>> x[0].append(1)
>>> x

[[1], [1], [1], [1], [1], [1], [1], [1], [1], [1], [1], [1], [1], [1],
[1], [1], ...

Nice one.

 

[Bart Willems]

For my code of radix sort, I need to initialize 256 buckets. My code
looks a little clumsy:

radix=[[]]
for i in range(255):
radix.append([])

any better code to initalize this list?

radix = [[[]]*256][0]

No I fell for that one too - it's the same as 'radix = [[]] * 256. Try
radix[0].append('dead parrot')..