How to create a list of tuples with adjacent list elements if a condition is true ?

The best way of approach:

[(x,y) for x,y in zip(myList, myList[1:]) if y == 9]

[(8, 9), (4, 9), (7, 9)]

The above code is explained here:

• zip(some_list, some_list[1:]) would generate a list of pairs of adjacent elements.
• Now with that tuple, filter on the condition that the second element is equal to 9.

we can also do it without slicing by creating iterators:

l = myList = [1,8,9,2,4,9,6,7,9,8]
 
it1, it2 = iter(l), iter(l)
# consume first element from it2 -> leaving 8,9,2,4,9,6,7,9,8
next(it2, "")
# then pair up, (1,8), (8,9) ...
print([(i, j) for i,j in zip(it1, it2) if j == 9])

Or use the pairwise recipe to create your pairs

from itertools import tee, izip
 
def pairwise(iterable):
    "s -> (s0,s1), (s1,s2), (s2, s3), ..."
    a, b = tee(iterable)
    next(b, None)
    return izip(a, b)

 Just import tee and use the regular zip for python3,

The code can be used to make Tuples with adjacent list elements

myList = [9, 1, 8, 9, 2, 4, 9, 6, 7, 9, 8]
 
[(myList[i-1], x) for i, x in enumerate(myList) if x==9 and i!=0]
 
# [(8, 9), (4, 9), (7, 9)]