Склейка нескольких текстовых файлов в один

import fileinput
 
first = True
with open("5.txt", "wt", encoding="cp1251") as out, fileinput.input(
        files=["{}.txt".format(i) for i in range(1, 5)]) as f:
    for line in f:
        if "next" in line:
            if not first:
                line = line.replace("next", "")
            else:
                first = False
        out.write(line)

lstr = []
for path in ['1.txt', '2.txt', '3.txt', '4.txt' ]:
    with open(path) as f:
         lstr.append(f.read())
         lstr.append('\n') #вроде это символ перевода строки, если нет то поправь
 
for idx, s in enumerate(lstr):
    a =  s.find('next')
    if a:
         lstr[idx] = s[:a] + s[(a+4):]
         break
 
with open('5.txt', 'a') as f:
     for s in lstr:
         f.write(s)

fileinput.input(
        files=["{}.txt".format(i) for i in range(1, 5)]), openhook=fileinput.hook_encoded("utf8"))

first = True
with open('5.txt', 'wt', encoding='utf8') as out:
    all_data = ''.join(
        [open('{}.txt'.format(i), encoding='utf8').read() for i in range(1, 5)]
    )
    for line in all_data.split('\n'):
        print(line)
        if 'next' in line:
            if not first:
                line = line.replace('next', '')
            else:
                first = False
        out.write(line + '\n')

TabError: inconsistent use of tabs and spaces in indentation?

import os
os.remove(filename)

import os
first = True
with open('5.txt', 'wt', encoding='utf8') as out:
* * all_data = ''.join(
* * * * [open('{}.txt'.format(i), encoding='utf8').read() for i in range(1, 5)]
* * )
* * for line in all_data.split('\n'):
* * * * print(line)
* * * * if 'next' in line:
* * * * * * if not first:
* * * * * * * * line = line.replace('next', '')
* * * * * * else:
* * * * * * * * first = False
* * * * out.write(line + '\n')
os.remove(1.txt)

os.remove('1.txt')