filename = 'cano.txt'

print('Løsning 1')

file = open(filename)
count = 0
line = file.readline()
while line != '':
    count += 1

    if 'mathematic' in line.lower():
        print(line, end='')

    line = file.readline()
file.close()

print('Løsning 2')

file = open(filename)
lines = file.readlines()
file.close()

for line in lines:
    if 'mathematic' in line.lower():
        print(line, end='')

print('Løsning 3')

file = open(filename)

for line in file:
    if 'mathematic' in line.lower():
        print(line, end='')

file.close()

import os
print('Løsning 4')

filename = 'canon.txt'

try:
    if os.path.isfile(filename):
        file = open(filename)
        try:
            for line in file:
                if 'mathematic' in line.lower():
                    print(line, end='')

             #   print(7 / 0)
        except ZeroDivisionError:
            print('lad nu være at dividere med nul!')
        finally:
            file.close()
    else:
        print('filen findes ikke')
except FileNotFoundError:
    print('øv...')


print('Løsning 5')

filename = 'cano.txt'
savename = 'selected_lines.txt'

with open(filename) as readfile:
    with open(savename, 'a') as savefile:
        for line in readfile:
            if 'mathematic' in line.lower():
#                print(line, file=savefile, end='')
                savefile.write(line)