File27. Дан файл целых чисел с элементами \(A_1, A_2, ..., A_N\) (N — количество элементов в файле). Заменить исходное расположение его элементов на следующее:
\(A_1, A_N, A_2, A_{N-1}, A_3, ...\) .

Решение на Python 3:

# -*- coding: utf-8 -*-
import random
import string
import os
import sys
import math

def GenerateReals(fname):
#generate random real numbers and save them to file
    N = random.randint(2,15)
    N = 9
    print("N = ",N)
    L = []
    x = round(random.uniform(0, 10),1)
    L.append(x)
    for i in range(1,N):
        lst_rnd = [round(random.uniform(0, 10),1) for _ in range(0,10)]
        try:
            lst_rnd.remove(x)
        except:
            pass
        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

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

file1 = "file27.txt"
GenerateReals(file1)
print("Read from:",file1)

try:
    #file for temporary data
    N = random.randrange(5,8)
    S = ''.join(random.choice(string.ascii_lowercase + string.ascii_uppercase \
        + string.digits) for _ in range(N))
    temp_file_1 = "temp_" + S + "_1.txt"
    temp_file_2 = "temp_" + S + "_2.txt"
    #print()
    print("Temp file 1:",temp_file_1)
    print("Temp file 2:",temp_file_2)

    N = CountFile(file1)
    N1 = int(math.ceil(N/2))
    N2 = N - int(N/2)

    with open(file1, 'r') as f_in, open(temp_file_1, 'w') as f_out:
        for i in range(1,N1+1):
            line = f_in.readline()
            print(i,":",line,end="")
            f_out.write(line)

    with open(temp_file_2, 'w') as f_out:
        for i in range(N,N2,-1):
            #print(i)
            line = GetLineK(file1,i)
            print(i,":",line,end="")
            f_out.write(line)

    with open(file1, 'w') as f_out, open(temp_file_1, 'r') as f_in1, \
         open(temp_file_2, 'r') as f_in2:
        for i in range(0,N2):
            line = f_in1.readline()
            f_out.write(line)
            line = f_in2.readline()
            f_out.write(line)
                
    #sys.exit()

    try:
        os.remove(temp_file_1)
        os.remove(temp_file_2)
    except OSError as e:
        print("\nError:", e)

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

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