historial-lineas.py

from collections import deque

def buscar(lineas, patron, historial=5):
    lineas_anteriores = deque(maxlength=historial)

    for linea in lineas:
        if pattern in linea:
            yield linea, lineas_anteriores

        lineas_anteriores.append(linea)

if __name__ == "__main__":
    with open ('libro_python.txt') as f:
        for linea, lineas_anteriores in buscar(f, 'python', 5):
            for linea_anterior in lineas_anteriores:
                print(linea_anterior, end='')

            print(linea, end='')
            print('-' * 20)