Python Strings as Comments

The question was:

In Python we can emulate multiline comments using triple-quoted strings, but conceptually strings and comments are very different. I.e. strings are objects, comments are auxillary text discarded at compile time. Strings are objects created at runtime, comments are not.

The answer from Steven D'Aprano:

Guido's time-machine strikes again.

>>> import dis
>>> def test():
...     x = 1
...     """
...     This is a triple-quote comment.
...     """
...     return x
...
>>> dis.dis(test)
  2           0 LOAD_CONST               1 (1)
              3 STORE_FAST               0 (x)

  6           6 LOAD_FAST                0 (x)
              9 RETURN_VALUE

String literals -- not just triple-quoted strings, but any string literal -- that don't go anywhere are discarded by the Python compiler, precisely so they can be used as comments.

But docstrings are something else

You would need to add specific options to python to stop it from byte-compiling docstrings though.

Anonymous

Re: But docstrings are something else

Sorry, for the late reply, I myself had do some experimentations to understand this stuff. In the above snippet as you saw, the compiler discards any string which is not referenced. But it is still available as a doc attribute of the test object.

>>> def test():

>>> import dis

>>> dis.dis(test)

3 0 LOAD_CONST 1 (1)

3 STORE_FAST 0 (x)

4 6 LOAD_FAST 0 (x)

9 RETURN_VALUE

>>> print test.doc

This is string

>>>

But create a python snippet 'foo.py' like this:

def test():

"""This is a docstring"""

print test.doc

return True

test()

and do python foo.py vs python -OO foo.py you will see the .doc attribute itself is discarded while doing optimization using -OO.

Senthil