Python: How to remove the last element in each tuple in a list

Question

Hey, I've got a list like

alist = [[a,b,(1,2)], [a,b,(1,2)], [a,b,(1,2)]]

I want to remove the third element from all the elements in alist, or it means the last one in the elements of a list

So the result will be

alist = [[a,b], [a,b], [a,b]]

Do we have any fast way to do this? Thanks!

Your script works in python shell, but does not work in my program, don't know why is that

happens.

I done the reading of Python quick book, heh~

rows = [[1,2,(1,2)],[1,2,(1,2)],[1,2,(1,2)]]
print rows
rows = [x[:-1] for x in rows] 
print rows

Answer 1

You could use list comprehension to create a new list that removes the last element.

>>> alist = [[1,2,(3,4)],[5,6,(7,8)],[9,10,(11,12)]]
>>> [x[:-1] for x in alist]       # <-------------
[[1, 2], [5, 6], [9, 10]]

However, if you want efficiency you could modify the list in-place:

>>> alist = [[1,2,(3,4)],[5,6,(7,8)],[9,10,(11,12)]]
>>> for x in alist: del x[-1]       # <-------------
... 
>>> alist
[[1, 2], [5, 6], [9, 10]]

Answer 2

This is basic Python stuff. You should be able to do it after reading the Python tutorial

>>> alist = [[1,2,(3,4)],[5,6,(7,8)],[9,10,(11,12)]]
>>> for li in alist:
...     print li[0:2]
...
[1, 2]
[5, 6]
[9, 10]
>>>

Later on, you can go to intermediate stuff like list comprehension etc