iterate through an irregular nested list in Python

Use a recursive iterator/generator:
It becomes a bit peculiar because you want special treatment for empty lists inside,
but otherwise it is quite standard Python:

aList = [[2,'jkj'],[],[],['kite',88,'ooo','pop','push','pull'],['hello']]

def reclist(aList):
for item in aList:
if isinstance(item, list):
if item == []:
yield ''
else:
yield from reclist(item)
else:
yield item

for i in reclist(aList):
print(i, end=',')

This gives you an extra comma at the end, unfortunately.
But it is the pattern for other types of processing.

Or use it like this:

print (','.join(str(i) for i in reclist(aList)))

--
Pieter van Oostrum
www: http://pieter.vanoostrum.org/
PGP key: [8DAE142BE17999C4]

Dan Stromberg

2020-03-06 18:00:50 UTC

It becomes a bit peculiar because you want special treatment for empty lists inside,
aList = [[2,'jkj'],[],[],['kite',88,'ooo','pop','push','pull'],['hello']]
yield ''
yield from reclist(item)
yield item
print(i, end=',')
This gives you an extra comma at the end, unfortunately.
But it is the pattern for other types of processing.
print (','.join(str(i) for i in reclist(aList)))

If your lists are nested to inconsistent depth, and you're on a modern
version of Python (3.3 and up), recursion with yield from (as above) is the
way to go.

If your lists are nested to a consistent depth (as your example seems to
suggest), you can just:

for sublist in aList:
for element in sublist:
yield element

If you need inconsistent depth and you're on an old version of python,
yield from is unavailable. In that case, it's best to write it out
recursively (even though that won't work really), and modify that to be
nonrecursive using an explicit stack or stacks. There's an example of this
at:
http://stromberg.dnsalias.org/svn/treap/trunk/m4_treap.m4
See iterator_macro.
Don't let the m4 throw you - it's just a way of deriving pure python and
cython from the same file.
You can generate the pure python form the .m4 file with simply: m4 -Dpy=1 <
m4_treap.m4 > py_treap.py
...if you install an m4 binary.

HTH.

Souvik Dutta

2020-03-06 16:18:13 UTC

A better way would be to just do
nestedl = [[2], [], [], [l, b, n]] #nested list
for a in nestedl: #taking all the sublist

for b in a: #iterating through the sub
print(b)

Though it is easy the only limitation is that it works only if the elements
are lists. Which we can be easily overcome by using an if statement to
check the elements type.

Post by s***@gmail.com
Hi All,
I am new to python.
I have a irregular nested lists in a list.
Please help me to iterate through each element.
Thanks much in advance.
Sample Ex
aList = [[2,'jkj'],[],[],['kite',88,'ooo','pop','push','pull'],['hello']]
2,jkj,,,kite,88,ooo,pop,push,pull,hello
--
https://mail.python.org/mailman/listinfo/python-list
Hi All,
I am new to python.
I have a irregular nested lists in a list.
Please help me to iterate through each element.
Thanks much in advance.
Sample Ex
aList = [[2,'jkj'],[],[],['kite',88,'ooo','pop','push','pull'],['hello']]
2,jkj,,,kite,88,ooo,pop,push,pull,hello
--
https://mail.python.org/mailman/listinfo/python-list

Souvik Dutta

2020-03-07 02:48:12 UTC

A better way would be to just do
nestedl = [[2], [], [], [l, b, n]] #nested list
for a in nestedl: #taking all the sublist

for b in a: #iterating through the sub
print(b)

Though it is easy the only limitation is that it works only if the elements are lists. Which we can be easily overcome by using an if statement to check the elements type.

Dan Stromberg

2020-03-06 15:00:50 UTC

It becomes a bit peculiar because you want special treatment for empty
lists inside,
aList = [[2,'jkj'],[],[],['kite',88,'ooo','pop','push','pull'],['hello']]
yield ''
yield from reclist(item)
yield item
print(i, end=',')
This gives you an extra comma at the end, unfortunately.
But it is the pattern for other types of processing.
print (','.join(str(i) for i in reclist(aList)))

If your lists are nested to inconsistent depth, and you're on a modern version of Python (3.3 and up), recursion with yield from (as above) is the way to go.

If your lists are nested to a consistent depth (as your example seems to suggest), you can just:

for sublist in aList:
for element in sublist:
yield element

If you need inconsistent depth and you're on an old version of python, yield from is unavailable. In that case, it's best to write it out recursively (even though that won't work really), and modify that to be nonrecursive using an explicit stack or stacks. There's an example of this at:
http://stromberg.dnsalias.org/svn/treap/trunk/m4_treap.m4
See iterator_macro.
Don't let the m4 throw you - it's just a way of deriving pure python and cython from the same file.
You can generate the pure python form the .m4 file with simply: m4 -Dpy=1 < m4_treap.m4 > py_treap.py
...if you install an m4 binary.

HTH.

Souvik Dutta

2020-03-07 02:48:12 UTC

A better way would be to just do
nestedl = [[2], [], [], [l, b, n]] #nested list
for a in nestedl: #taking all the sublist

for b in a: #iterating through the sub
print(b)

Though it is easy the only limitation is that it works only if the elements are lists. Which we can be easily overcome by using an if statement to check the elements type.

Dan Stromberg

2020-03-06 15:00:50 UTC

It becomes a bit peculiar because you want special treatment for empty
lists inside,
aList = [[2,'jkj'],[],[],['kite',88,'ooo','pop','push','pull'],['hello']]
yield ''
yield from reclist(item)
yield item
print(i, end=',')
This gives you an extra comma at the end, unfortunately.
But it is the pattern for other types of processing.
print (','.join(str(i) for i in reclist(aList)))

If your lists are nested to inconsistent depth, and you're on a modern version of Python (3.3 and up), recursion with yield from (as above) is the way to go.

If your lists are nested to a consistent depth (as your example seems to suggest), you can just:

for sublist in aList:
for element in sublist:
yield element

If you need inconsistent depth and you're on an old version of python, yield from is unavailable. In that case, it's best to write it out recursively (even though that won't work really), and modify that to be nonrecursive using an explicit stack or stacks. There's an example of this at: http://stromberg.dnsalias.org/svn/treap/trunk/m4_treap.m4
See iterator_macro.
Don't let the m4 throw you - it's just a way of deriving pure python and cython from the same file.
You can generate the pure python form the .m4 file with simply: m4 -Dpy=1 < m4_treap.m4 > py_treap.py
...if you install an m4 binary.

HTH.

Pieter van Oostrum

2020-03-06 20:54:40 UTC

Use a recursive iterator/generator: It becomes a bit peculiar because you want special treatment for empty lists inside, but otherwise it is quite standard Python:

aList = [[2,'jkj'],[],[],['kite',88,'ooo','pop','push','pull'],['hello']]

def reclist(aList):
for item in aList:
if isinstance(item, list):
if item == []:
yield ''
else:
yield from reclist(item)
else:
yield item

for i in reclist(aList):
print(i, end=',')

This gives you an extra comma at the end, unfortunately. But it is the pattern for other types of processing.

Or use it like this:

print (','.join(str(i) for i in reclist(aList)))

--
Pieter van Oostrum
www: http://pieter.vanoostrum.org/
PGP key: [8DAE142BE17999C4]

Souvik Dutta

2020-03-07 02:48:12 UTC

A better way would be to just do
nestedl = [[2], [], [], [l, b, n]] #nested list
for a in nestedl: #taking all the sublist

for b in a: #iterating through the sub
print(b)

Though it is easy the only limitation is that it works only if the elements are lists. Which we can be easily overcome by using an if statement to check the elements type.

Dan Stromberg

2020-03-06 15:00:50 UTC

It becomes a bit peculiar because you want special treatment for empty
lists inside,
aList = [[2,'jkj'],[],[],['kite',88,'ooo','pop','push','pull'],['hello']]
yield ''
yield from reclist(item)
yield item
print(i, end=',')
This gives you an extra comma at the end, unfortunately.
But it is the pattern for other types of processing.
print (','.join(str(i) for i in reclist(aList)))

If your lists are nested to inconsistent depth, and you're on a modern version of Python (3.3 and up), recursion with yield from (as above) is the way to go.

If your lists are nested to a consistent depth (as your example seems to suggest), you can just:

for sublist in aList:
for element in sublist:
yield element

If you need inconsistent depth and you're on an old version of python, yield from is unavailable. In that case, it's best to write it out recursively (even though that won't work really), and modify that to be nonrecursive using an explicit stack or stacks. There's an example of this at: http://stromberg.dnsalias.org/svn/treap/trunk/m4_treap.m4
See iterator_macro.
Don't let the m4 throw you - it's just a way of deriving pure python and cython from the same file.
You can generate the pure python form the .m4 file with simply: m4 -Dpy=1 < m4_treap.m4 > py_treap.py
...if you install an m4 binary.

HTH.

Dan Stromberg

2020-03-06 15:00:50 UTC

It becomes a bit peculiar because you want special treatment for empty
lists inside,
aList = [[2,'jkj'],[],[],['kite',88,'ooo','pop','push','pull'],['hello']]
yield ''
yield from reclist(item)
yield item
print(i, end=',')
This gives you an extra comma at the end, unfortunately.
But it is the pattern for other types of processing.
print (','.join(str(i) for i in reclist(aList)))

If your lists are nested to inconsistent depth, and you're on a modern version of Python (3.3 and up), recursion with yield from (as above) is the way to go.

If your lists are nested to a consistent depth (as your example seems to suggest), you can just:

for sublist in aList:
for element in sublist:
yield element

If you need inconsistent depth and you're on an old version of python, yield from is unavailable. In that case, it's best to write it out recursively (even though that won't work really), and modify that to be nonrecursive using an explicit stack or stacks. There's an example of this at: http://stromberg.dnsalias.org/svn/treap/trunk/m4_treap.m4
See iterator_macro.
Don't let the m4 throw you - it's just a way of deriving pure python and cython from the same file.
You can generate the pure python form the .m4 file with simply: m4 -Dpy=1 < m4_treap.m4 > py_treap.py
...if you install an m4 binary.

HTH.

Pieter van Oostrum

2020-03-06 20:54:40 UTC

Use a recursive iterator/generator: It becomes a bit peculiar because you want special treatment for empty lists inside, but otherwise it is quite standard Python:

aList = [[2,'jkj'],[],[],['kite',88,'ooo','pop','push','pull'],['hello']]

def reclist(aList):
for item in aList:
if isinstance(item, list):
if item == []:
yield ''
else:
yield from reclist(item)
else:
yield item

for i in reclist(aList):
print(i, end=',')

This gives you an extra comma at the end, unfortunately. But it is the pattern for other types of processing.

Or use it like this:

print (','.join(str(i) for i in reclist(aList)))

--
Pieter van Oostrum
www: http://pieter.vanoostrum.org/
PGP key: [8DAE142BE17999C4]

Dan Stromberg

2020-03-06 15:00:50 UTC

It becomes a bit peculiar because you want special treatment for empty
lists inside,
aList = [[2,'jkj'],[],[],['kite',88,'ooo','pop','push','pull'],['hello']]
yield ''
yield from reclist(item)
yield item
print(i, end=',')
This gives you an extra comma at the end, unfortunately.
But it is the pattern for other types of processing.
print (','.join(str(i) for i in reclist(aList)))

If your lists are nested to inconsistent depth, and you're on a modern version of Python (3.3 and up), recursion with yield from (as above) is the way to go.

If your lists are nested to a consistent depth (as your example seems to suggest), you can just:

for sublist in aList:
for element in sublist:
yield element

If you need inconsistent depth and you're on an old version of python, yield from is unavailable. In that case, it's best to write it out recursively (even though that won't work really), and modify that to be nonrecursive using an explicit stack or stacks. There's an example of this at: http://stromberg.dnsalias.org/svn/treap/trunk/m4_treap.m4
See iterator_macro.
Don't let the m4 throw you - it's just a way of deriving pure python and cython from the same file.
You can generate the pure python form the .m4 file with simply: m4 -Dpy=1 < m4_treap.m4 > py_treap.py
...if you install an m4 binary.

HTH.

Souvik Dutta

2020-03-07 02:48:12 UTC

s***@gmail.com 2020-03-06 12:59:26 UTC

A better way would be to just do
nestedl = [[2], [], [], [l, b, n]] #nested list
for a in nestedl: #taking all the sublist

for b in a: #iterating through the sub
print(b)

Though it is easy the only limitation is that it works only if the elements are lists. Which we can be easily overcome by using an if statement to check the elements type.

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Pieter van Oostrum 2020-03-06 14:54:40 UTC

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Pieter van Oostrum 2020-03-06 20:54:40 UTC

Pieter van Oostrum 2020-03-06 20:54:40 UTC