Content Addressable Python! (work in progress)

cap.py

import dill


x = 1


def print_globals(max_value_len=79):
    """
    >>> print_globals(40)  # doctest: +ELLIPSIS
    globals: {
      ...
      '__doc__': ...
      '__package__': ...
      '__loader__': <_frozen_importlib_e…ject at 0x...>
      '__spec__': ModuleSpec(name='...')
      '__file__': '...'
      '__cached__': '...'
      '__builtins__': {'__name__': 'builti… object., '_': None}
      ...
      'print_globals': <function print_globals at 0x...>
      ...
    }
    """
    print('globals: {')
    for k, v in globals().items():
        r = repr(v)
        if len(r) > max_value_len:
            half = int(max_value_len / 2)
            r = r[:half] + '…' + r[-half:]
        print(f"  {k!r}: {r}")
    print('}')


def stuff():
    global x
    x += 1
    print(f"x is now {x}")


if __name__ == '__main__':
    import os
    from hashlib import sha256

    # with open(__file__) as f:
    #     code = f.read()
    # bytecode = compile(code, '__main__', 'exec')
    # bytecode_hash = sha256(bytecode.co_code).hexdigest()

    with open(__file__, 'rb') as f:
        code = f.read()
    code_hash = sha256(code).hexdigest()

    import sys
    _, *args = sys.argv
    try:
        start_from, = args
    except ValueError:
        start_from = None

    if start_from is None:
        print(f"Starting fresh session for {code_hash}")
        try:
            os.makedirs(f'sessions/{code_hash}')
        except FileExistsError:
            pass
        else:
            with open(f'sessions/{code_hash}/code.py', 'wb') as f:
                f.write(code)
    else:
        print(f"Loading session {start_from!r}")
        dill.load_session(f'sessions/{code_hash}/{start_from}.pkl')

    print_globals()
    print(f"Doing stuff")
    stuff()
    print(f"Done doing stuff")
    print_globals()

    temp_path = f'sessions/{code_hash}/tmp.pkl'
    dill.dump_session(temp_path)
    with open(temp_path, 'rb') as f:
        state_hash = sha256(f.read()).hexdigest()
    new_path = f'sessions/{code_hash}/{state_hash}.pkl'
    os.rename(temp_path, new_path)

    prev_path = f'sessions/{code_hash}/prev.pkl'
    try:
        os.remove(prev_path)
    except FileNotFoundError:
        pass
    os.link(new_path, prev_path)

    print(f"Saved state {state_hash}")