$ echo "print('hello from PYTHONSTARTUP')" > /tmp/foo.py
$ PYTHON_BASIC_REPL=1 PYTHONSTARTUP=/tmp/foo.py ./python
Python 3.15.0a0 (heads/basic_repl_error_reporting:3d46e8feed, Aug 10 2025, 21:12:17) [GCC 12.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
hello from PYTHONSTARTUP
>>> 1/0
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
    1/0
    ~^~
ZeroDivisionError: division by zero

$ echo "def foo(x):  return 1/x" > /tmp/foo.py
$ PYTHON_BASIC_REPL=1 PYTHONSTARTUP=/tmp/foo.py ./python
Python 3.15.0a0 (heads/basic_repl_error_reporting:3d46e8feed, Aug 10 2025, 21:12:17) [GCC 12.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> def bar(x):
...     return foo(x)
... 
>>> bar(0)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
    bar(0)
    ~~~^^^
  File "<stdin>", line 2, in bar
    return foo(x)
  File "/tmp/foo.py", line 1, in foo
    def foo(x):  return 1/x
                        ~^~
ZeroDivisionError: division by zero