Krendelev

w2 = "космодром"

with open("base.txt") as bh:
    lines = [line for line in bh]
    
with open("base.txt", "w") as bh, open("deleted.txt", "w") as dh:
    handler = {True: dh, False: bh}
    for line in lines:
        handler[w2 in line].write(line)
    w3 = None if dh.tell() else w2