redirect standard output problem

[iMath]

redirect standard output problem

why the result only print A but leave out 888 ?

import sys
class RedirectStdoutTo:

    def __init__(self, out_new):
        self.out_new = out_new
    def __enter__(self):
        sys.stdout = self.out_new
    def __exit__(self, *args):
        sys.stdout = sys.__stdout__


print('A')
with open('out.log', mode='w', encoding='utf-8') as a_file, RedirectStdoutTo(a_file):

    print('B')
    print('C')

print(888)