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I know in c++ it already exist
#include <list>
Now I am curious to know if it exist in python also.
You can also take a look at llist python package, which provides some useful features that deque does not. There are not only doubly linked lists, but also single linked lists data structure in that package. IMHO, one of the biggest advantages of this package is the ability to store a reference to the llist elements.
It appears that collections.deque is a doubly-linked-list library in Python. According to the documentation, it should have approximately O(1) cost when appending or popping from the head or the tail, as well as O(n) for regular inserts (which matches what we'd expect from a linked list).
API: http://docs.python.org/2/library/collections.html#collections.deque
Source: https://stackoverflow.com/a/282238/2441252
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I would like to get some understanding on how the data types in python - list, tuple, dict and set - are implemented
How are they implemented, importantly the data structure used.
Any place/ url to precisely get this understanding?
The best place to look is the CPython implementation source code:
dict - Hash map targeting fast resolution of keys
list - Looks like an array of PyObjects
tuple - Same as list but with optimisations that a tuple can allow (fixed size, objects)
set - Hash map with optimisations for cache locality
The source code is heavily commented and well written C. This would be the best place to understand the data structures used in detail.
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I have a large sparse matrix (lil) implemented in Python with scipy, which comprises of Users on one axis, and songs they played on the other. So each row is a linked list of the songs that user has played.
I need to split each row ( user's songs ) so i have training and test data, but I'm unsure of how to do this. Sorry, im new to python, any help would be greatly appreciated.
I think you need sklearn.cross_validation.train_test_split
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I have started learning Python and was wondering how to make a loop, I cant find a website that has it so if you knew it would be great!
I assume you mean a for loop. You do it like so:
for i in range(10):
print i
This is the simplest way. You can use xrange rather than range for very long loops to help with memory management.
Also there are ways to iterate through iterable objects (like lists, arrays, strings etc.):
a=[1,2,3]
for something in a:
print something
You could also use comprehension to make the code shorter, but that's a bit more advanced and you probably don't need it just yet. Should you so wish to learn what it's about this looks OK for a start.
There are many ways.
while True:
That loops until you put break on a line.
The two Aleksander Lidtke mentioned.
for x in range(10): #Loops through the following code 10 times
And:
x = [1,2,3,4]
for items in x: #the variable items is assigned to
#each variable as it iterates through
To learn more about python, read this book.
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I would like to know whether it is possible to carry out such an operation, that one picture is placed into another one at exact coordinates, automatedly.
I have a set consisting of 20 pairs of images of fixed size. I need to merge the pairs by placing first image of a pair to a fixed position on the second image.
I might need to do this mergers several times in future, so I am interested if there is a chance to write a scrypt in Python/Perl or any other simple language to handle this task. I am now using GIMP scripts, but most of the work still needs to be carried out manually...
Anyway, if this is not an option, I am asking someone to be so kind and briefly explain why is it so.
Thanks!
a lot of recepies ImageMagick v6 Examples -- Compositing Images. And you need perl-magick.
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Are there any python libraries for data trees?
I mean a tree as a general data structure, not just an xml tree.
(Like in this question, but in python.)
I'm happy with treelib. It addresses my problem. Could use a bit more documentation though. But the code is clear.
pypi, the Python Package Index, suggests tinytree, treedict, caxes, pyavl... these are just the top few after filtering away the many accidental hits (which point to specific tree such as XML ones, AST ones, etc, etc;-). If you clarify what you want to do with your trees it may be easier to suggest a specific package.
Although the ETE library seems to be originally developed to work with Phylogenetic trees, it implements many general features to work with any type of hierarchical tree structures, including programmatic tree drawing and visualization.
There is a comprehensive tutorial and a reference guide, in case you want to explore it.
python-graph seems to be a fairly thorough and complete package, and can export DOT graphs for use with Graphviz.
You probably want to look at cElementTree.