Comments are used to annotate, describe, or explain code that is complex or difficult to understand. Python will intentionally ignore comments when it compiles to bytecode by the interpreter. PEP 8 has a section dealing with comments.

Block and inline comments start with a #, followed by a space before the comment:

# This is a block comment.
print('Hello world!') # This is an inline commment.

Python does not include a formal way to write multiline comments. Each line of a comment spanning multiple lines should start with # and a space:

# This is the first line of a multiline comment.
# This is the second line.

Another type of comment is the docstring, documented in PEP 257. Docstrings are a specific type of comment that becomes the __doc__ attribute.

For a string literal to be a docstring, it must start and end with \"\"\" and be the first statement of the module, function, class, or method definition it is documenting:

class SomeClass():
    """Summary line for SomeClass.

    More elaborate descriptions may require using a
    a multiline docstring.
    """

    def method_a(self):
        """Single line summary of method_a."""
        pass

String literals that start and end with """ that are not docstrings (not the first statement), can be used for multiline strings. They will not become __doc__ attributes. If they are not assigned to a variable, they will not generate bytecode. There is some discussion about using them as multiline comments found here.

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