# change based on old/new vlaues

import platform

# creates user system variables
varRoot_old = nuke.getInput('Old File Root', 'E:/')
varRoot_new = nuke.getInput('New File Root', 'E:/someotherfolder/')

# make sure that the file paths end in a backslash (/)
if varRoot_old[ len(varRoot_old) - 1 ] != '/':
    varRoot_old += '/'
if varRoot_new[ len(varRoot_new) - 1 ] != '/':
    varRoot_new += '/'

# create a list of all of only the Read nodes in the Nuke script
a = nuke.allNodes('Read')

i = 0
for n in a:
    # set the working node from the list of nodes based on it's name
    b = nuke.toNode(a[i].name())

    # get the file path for the current node
    c = b['file'].getValue()

    # change from the old root path to the new root path
    d = c.replace(varRoot_old, varRoot_new)

    # replace the file path with the new file path
    b['file'].setValue(d)

    i += 1