Bash command with pipe('|') alway return exit code of 0, even in error case

Question

Code

a.py

import sys
import errno


def main():
    try:
        raise Exception("asdf")
        sys.stdout.write('{"v1": "kk"}')
        sys.stdout.flush()
    except IOError as e:
        # This catching exception is for preventing 'Broken Pipe' error
        # ref: https://www.geeksforgeeks.org/broken-pipe-error-in-python/
        if e.errno == errno.EPIPE:
          pass 

if __name__ == "__main__":
    main()

b.py

import io
import sys


def main():
    # Getting input from the previous process's std output
    input_messages = io.TextIOWrapper(sys.stdin.buffer, encoding='utf-8')
    for message in input_messages:
        print(message)


if __name__ == '__main__':
    main()

1. Experiment 1

1.1 a.sh

echo $?   # print 'exit code'
python a.py   
echo $?

1.2 Execution result

$ sh a.sh
>> 
0
Traceback (most recent call last):
  File "/Users/chois/Dropbox/Programming/Workspace/chois_workflow/data_ingestor/a.py", line 67, in <module>
    main()
  File "/Users/chois/Dropbox/Programming/Workspace/chois_workflow/data_ingestor/a.py", line 57, in main
    raise Exception("asdf")
Exception: asdf
1

--> Exit code is 1 due to the exception

2. Experiment 2

2.1 a.sh

echo $?   # print 'exit code'
python a.py | python b.py
echo $?

2.2 Execution result

$ sh a.sh
>> 
0
Traceback (most recent call last):
  File "a.py", line 67, in <module>
    main()
  File "a.py", line 57, in main
    raise Exception("asdf")
Exception: asdf
0

--> Exit code is still 0, even process has an error.

How can I make the command with pipe have exit code of 1?