Q:

How to add a number to a concatenative pair of coordinates within a sublist consecutively?

I have the following list of coordinates:
coords=[[(1,2),(3,4),(5,6)], [(7,8),(9,10)], [(11,12),(13,14),(15,16),(17,18)]]

Now I to converted it to a following list using the 
[m for n in coords for m in zip(n, n[1:])]

coords=[((1,2),(3,4)), ((3,4),(5,6)), ((7,8),(9,10)), ((11,12),(13,14)), ((13,14),(15,16)), ((15,16),(17,18))]

so now I like to add a constant value (does not matter the value) to the first set (x+a,y+a) coordinates from previous list such as the following:
coords=[((1,2),(3,4)), ((3+a,4+a),(5,6)), ((7,8),(9,10)), ((11,12),(13,14)), ((13+a,14+a),(15,16)), ((15+a,16+a),(17,18))]

My intention is make the shared coordinates slightly different so that they have not intersected.

A:

This code will do it:
x = [m if i == 0 else ((m[0][0] + a, m[0][1] + a), m[1]) for n in coords for i, m in enumerate(zip(n, n[1:]))]

Explanation:
in coords you have items like ((1,2),(3,4)), ((3+a,4+a),(5,6)), you should add a to all first tuples in item except first group
for i, m in enumerate(zip(n, n[1:])) returns item in format index_of_item, item
m if i == 0 else ((m[0][0] + a, m[0][1] + a), m[1])
Don't modify tuple for first element, else add a to first tuple of 2

