File30. Дан файл целых чисел, содержащий четное количество элементов. Удалить из данного файла вторую половину элементов.

Решение на Python 3:

# -*- coding: utf-8 -*-
import random

def GenerateNumbers(fname):
    N = random.randint(1,10) * 2
    print("N = ",N)
    L = []
    x = random.randrange(1,10)
    L.append(x)
    for i in range(1,N):
        lst_rnd = list(range(1,10))
        lst_rnd.remove(x)
        x = random.choice(lst_rnd)
        L.append(x)
    print(L)
    try:
        f = open(fname, "w")
        try:
            for x in L:
                line = str(x)+"\n"
                f.write(line)
        finally:
            f.close()
    except IOError:
        print('Write error: ',fname)

def CountFile(fname):
#count number of rows in given text-file 
    N = 0
    try:
        with open(fname,'r') as f:
            for line in f:
                N += 1
                #print(N,":",line)
    except IOError:
        print("Open error:",fname)
        return -1
    finally:
        return N

f_input = "file30_in.txt"
f_output = "file30_out.txt"
GenerateNumbers(f_input)
print("Read from:",f_input)
print("Write to:",f_output)

N = CountFile(f_input)
N = int(round(N/2.0))

try:
    with open(f_input, 'r') as f_in, open(f_output, 'w') as f_out:
        for i in range(N):
            line = f_in.readline()
            f_out.write(line)

except IOError:
    print('Open error: ',file1)