Nested lists, simple though

[Zethex]

Im a bit new to python. Anyway working on a little project of mine and i
have nested lists

ie

Answer = [['computer', 'radeon', 'nvidia'], ['motherboard', 'asus']]

and so forth..,
Anyway the amount of [[]] do increase over time. Im just wondering is there
a simple way to add these together so they become 1 simple list, so it would
be ['computer'....'asus'] etc without the nested list. Its random the
amount each time so i cant just go a[0]+a[1].
Thank you if you can help

 

[sturlamolden]

Anyway the amount of [[]] do increase over time. Im just wondering is there
a simple way to add these together so they become 1 simple list, so it would
be ['computer'....'asus'] etc without the nested list. Its random the
amount each time so i cant just go a[0]+a[1].
Thank you if you can help

Does this answer your question?

a = [1,2,3]
a.extend([4,5,6])
a

[1, 2, 3, 4, 5, 6]

 

[Jason Scheirer]

Im a bit new to python.  Anyway working on a little project of mine and i
have nested lists

ie

Answer = [['computer', 'radeon', 'nvidia'], ['motherboard', 'asus']]

and so forth..,
Anyway the amount of [[]] do increase over time.  Im just wondering is there
a simple way to add these together so they become 1 simple list, so it would
be ['computer'....'asus'] etc without the nested list.  Its random the
amount each time so i cant just go a[0]+a[1].
Thank you if you can help

The first idea that comes to mind is reduce(lambda x, y: x + y,
list_of_lists, [])

 

[George Sakkis]

Im a bit new to python.  Anyway working on a little project of mine and i
have nested lists

ie

Answer = [['computer', 'radeon', 'nvidia'], ['motherboard', 'asus']]

and so forth..,
Anyway the amount of [[]] do increase over time.  Im just wondering is there
a simple way to add these together so they become 1 simple list, so it would
be ['computer'....'asus'] etc without the nested list.  Its random the
amount each time so i cant just go a[0]+a[1].
Thank you if you can help
--

The first idea that comes to mind is reduce(lambda x, y: x + y,
list_of_lists, [])

s/first/worst/

There, I fixed it for you.

 

[sturlamolden]

Anyway the amount of [[]] do increase over time.

You can flatten a nested list using a closure and recursion:

def flatten(lst):
tmp = []
def _flatten(lst):
for elem in lst:
if type(elem) != list:
tmp.append(elem)
else:
_flatten(elem)
_flatten(lst)
return tmp


However, CPython does not recurse very fast, but Cython and Pyrex do.
First, get rid of the closure, it is not supported in Cython or Pyrex
(at least not yet). Then change the recursive function to a cdef, i.e.
a normal C function which is called without the overhead of Python's
attribute lookup:

cdef _flatten(lst, tmp):
for elem in lst:
if type(elem) != list:
tmp.append(elem)
else:
_flatten(elem, tmp)

def flatten(lst):
tmp = []
_flatten(lst, tmp)
return tmp

Compile this with Cython or Pyrex, and you get a very fast nested list
flattener.

This also shows how easy it is to boost the performance of Python code
using Cython.

 

[sturlamolden]

This also shows how easy it is to boost the performance of Python code
using Cython.

We can improve this further by getting rid of the tmp.append attribue
lookup:

cdef _flatten(lst, append):
for elem in lst:
if type(elem) != list:
append(elem)
else:
_flatten(elem, append)

def flatten(lst):
tmp = []
_flatten(lst, tmp.append)
return tmp

 

[Diez B. Roggisch]

The first idea that comes to mind is reduce(lambda x, y: x + y,

list_of_lists, [])

Which is not helping for arbitrary nested lists, as the OP wanted.

Diez