What is a Docstring?

  • A docstring is a string literal that occurs as the first statement in a module, function, class, or method definition. Such a docstring becomes the __doc__ special attribute of that object.


  • All modules should normally have docstrings.

  • All functions and classes exported by a module should have docstrings.

  • Public methods (including the __init__ constructor) should also have docstrings.

  • A package may be documented in the module docstring of the file in the package directory.

  • For consistency, always use """``*triple double quotes*”””`` around docstrings. Use r"""``*raw triple double quotes*”””`` if you use any backslashes in your docstrings. For Unicode docstrings, use u"""Unicode triple-quoted strings""".

One-line Docstrings

One-liners are for really obvious cases. They should really fit on one line. For example:

def kos_root(self):
    """Return the pathname of the KOS root directory."""
    return self._kos_root


  • Triple quotes are used even though the string fits on one line. This makes it easy to later expand it.

  • The closing quotes are on the same line as the opening quotes. This looks better for one-liners.

  • There’s no blank line either before or after the docstring.

  • The docstring is a phrase ending in a period. It prescribes the function or method’s effect as a command (”Do this”, “Return that”), not as a description; e.g. don’t write “Returns the pathname …”.

  • The one-line docstring should NOT be a “signature” reiterating the function/method parameters (which can be obtained by introspection). Don’t do:

    def function(a, b):
        """function(a, b) -> list"""

    However, the nature of the return value cannot be determined by introspection, so it should be mentioned. The preferred form for such a docstring would be something like:

    def function(a, b):
        """Do X and return a list."""

Multi-line Docstrings

  • Multi-line docstrings consist of a summary line just like a one-line docstring, followed by a blank line, followed by a more elaborate description.

  • The summary line may be used by automatic indexing tools; it is important that it fits on one line and is separated from the rest of the docstring by a blank line.

  • The summary line may be on the same line as the opening quotes or on the next line (17/02/2011, I like it on the next line).

  • The entire docstring is indented the same as the quotes at its first line (see example below).

    def complex(real=0.0, imag=0.0):
        Form a complex number.
        Keyword arguments:
        real -- the real part (default 0.0)
        imag -- the imaginary part (default 0.0)
        if imag == 0.0 and real == 0.0: return complex_zero


  • Insert a blank line before and after all docstrings (one-line or multi-line) that document a class - generally speaking, the class’s methods are separated from each other by a single blank line, and the docstring needs to be offset from the first method by a blank line; for symmetry, put a blank line between the class header and the docstring.

  • The docstring for a class should summarize its behavior and list the public methods and instance variables.

  • If the class is intended to be subclassed, and has an additional interface for subclasses, this interface should be listed separately (in the docstring).

  • The class constructor should be documented in the docstring for its __init__ method.

  • Individual methods should be documented by their own docstring.

  • If a class subclasses another class and its behavior is mostly inherited from that class, its docstring should mention this and summarize the differences.

    Use the verb “override” to indicate that a subclass method replaces a superclass method and does not call the superclass method; use the verb “extend” to indicate that a subclass method calls the superclass method (in addition to its own behavior).

Functions and Methods

  • Docstrings documenting functions or methods generally don’t have the requirement to insert a blank line before and after, unless the function or method’s body is written as a number of blank-line separated sections - in this case, treat the docstring as another section, and precede it with a blank line.

  • The docstring for a function or method should summarize its behavior and document its arguments, return value(s), side effects, exceptions raised, and restrictions on when it can be called (all if applicable).

  • Optional arguments should be indicated.

  • It should be documented whether keyword arguments are part of the interface.

  • The docstring should document the argument names. It is best to list each argument on a separate line (see example above).

Modules and Packages

  • The docstring for a module should generally list the classes, exceptions and functions (and any other objects) that are exported by the module, with a one-line summary of each (these summaries generally give less detail than the summary line in the object’s docstring.)

  • The docstring for a package (i.e., the docstring of the package’s module) should also list the modules and subpackages exported by the package.


  • The docstring of a script (a stand-alone program) should be usable as its “usage” message, printed when the script is invoked with incorrect or missing arguments (or perhaps with a “-h” option, for “help”).

    Such a docstring should document the script’s function and command line syntax, environment variables, and files.

    Usage messages can be fairly elaborate (several screens full) and should be sufficient for a new user to use the command properly, as well as a complete quick reference to all options and arguments for the sophisticated user.


Use the help method to view the docstring comments for a class:

>>> from trac.ticket import Ticket
>>> help(Ticket)