Are Python docstrings and comments stored in memory when a module is loaded?

Question

Are Python docstrings and comments stored in memory when a module is loaded?

I've wondered if this is true, because I usually document my code well; may this affect memory usage?

Usually every Python object has a __doc__ method. Are those docstrings read from the file, or processed otherwise?

I've done searches here in the forums, Google and Mailing-Lists, but I haven't found any relevant information.

Do you know better?

Answer 1

As other answers mentioned, comments are discarded in compilation process but docstrings are stored in .pyc file and are loaded into the memory.

In .pyc files, there are code objects that are serialized with marshal. Although it's not supposed to be readable but you can still find something. So why not just see that it is indeed in .pyc file?

import marshal

text = '''def fn():
    """ZZZZZZZZZZZZZZZZZZ"""
    # GGGGGGGGGGGGGGGGGGG'''

code_object = compile(text, '<string>', 'exec')
serialized = marshal.dumps(code_object)
print(serialized)
print(b"ZZZZZZZZZZZZZZZZZZ" in serialized)
print(b"GGGGGGGGGGGGGGGGGGG" in serialized)

output:

b'\xe3\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00@\x00\x00\x00s\x0c\x00\x00\x00d\x00d\x01\x84\x00Z\x00d\x02S\x00)\x03c\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00C\x00\x00\x00s\x04\x00\x00\x00d\x01S\x00)\x02Z\x12ZZZZZZZZZZZZZZZZZZN\xa9\x00r\x01\x00\x00\x00r\x01\x00\x00\x00r\x01\x00\x00\x00\xfa\x08<string>\xda\x02fn\x01\x00\x00\x00s\x02\x00\x00\x00\x00\x01r\x03\x00\x00\x00N)\x01r\x03\x00\x00\x00r\x01\x00\x00\x00r\x01\x00\x00\x00r\x01\x00\x00\x00r\x02\x00\x00\x00\xda\x08<module>\x01\x00\x00\x00\xf3\x00\x00\x00\x00'
True
False

where is it referenced in the function's code object? in .co_consts

new_code_object = marshal.loads(serialized)
print(new_code_object.co_consts[0].co_consts[0])

output:

ZZZZZZZZZZZZZZZZZZ

---

def fn():
    """ZZZZZZZZZZZZZZZZZZ"""
    # GGGGGGGGGGGGGGGGGGG

print(fn.__code__.co_consts[0] is fn.__doc__) # True

Answer 2

Yes the docstrings are read from the file, but that shouldn't stop you writing them. Never ever compromise readability of code for performance until you have done a performance test and found that the thing you are worried about is in fact the bottleneck in your program that is causing a problem. I would think that it is extremely unlikely that a docstring will cause any measurable performance impact in any real world situation.