Adding docstrings to namedtuples?

Question

Is it possible to add a documentation string to a namedtuple in an easy manner?

I tried

from collections import namedtuple

Point = namedtuple("Point", ["x", "y"])
"""
A point in 2D space
"""

# Yet another test

"""
A(nother) point in 2D space
"""
Point2 = namedtuple("Point2", ["x", "y"])

print Point.__doc__ # -> "Point(x, y)"
print Point2.__doc__ # -> "Point2(x, y)"

but that doesn't cut it. Is it possible to do in some other way?

Answer 1

Came across this old question via Google while wondering the same thing.

Just wanted to point out that you can tidy it up even more by calling namedtuple() right from the class declaration:

from collections import namedtuple

class Point(namedtuple('Point', 'x y')):
    """Here is the docstring."""

Answer 2

You can achieve this by creating a simple, empty wrapper class around the returned value from namedtuple. Contents of a file I created (nt.py):

from collections import namedtuple

Point_ = namedtuple("Point", ["x", "y"])

class Point(Point_):
    """ A point in 2d space """
    pass

Then in the Python REPL:

>>> print nt.Point.__doc__
 A point in 2d space 

Or you could do:

>>> help(nt.Point)  # which outputs...

Help on class Point in module nt:

class Point(Point)
 |  A point in 2d space
 |  
 |  Method resolution order:
 |      Point
 |      Point
 |      __builtin__.tuple
 |      __builtin__.object
 ...

If you don't like doing that by hand every time, it's trivial to write a sort-of factory function to do this:

def NamedTupleWithDocstring(docstring, *ntargs):
    nt = namedtuple(*ntargs)
    class NT(nt):
        __doc__ = docstring
    return NT

Point3D = NamedTupleWithDocstring("A point in 3d space", "Point3d", ["x", "y", "z"])

p3 = Point3D(1,2,3)

print p3.__doc__

which outputs:

A point in 3d space

Answer 3

You could concoct your own version of the namedtuple factory function by Raymond Hettinger and add an optional docstring argument.  However it would be easier -- and arguably better -- to just define your own factory function using the same basic technique as in the recipe.  Either way, you'll end up with something reusable.

from collections import namedtuple

def my_namedtuple(typename, field_names, verbose=False,
                 rename=False, docstring=''):
    '''Returns a new subclass of namedtuple with the supplied
       docstring appended to the default one.

    >>> Point = my_namedtuple('Point', 'x, y', docstring='A point in 2D space')
    >>> print Point.__doc__
    Point(x, y):  A point in 2D space
    '''
    # create a base class and concatenate its docstring and the one passed
    _base = namedtuple(typename, field_names, verbose, rename)
    _docstring = ''.join([_base.__doc__, ':  ', docstring])

    # fill in template to create a no-op subclass with the combined docstring
    template = '''class subclass(_base):
        %(_docstring)r
        pass\n''' % locals()

    # execute code string in a temporary namespace
    namespace = dict(_base=_base, _docstring=_docstring)
    try:
        exec template in namespace
    except SyntaxError, e:
        raise SyntaxError(e.message + ':\n' + template)

    return namespace['subclass']  # subclass object created

Answer 4

I created this function to quickly create a named tuple and document the tuple along with each of its parameters:

from collections import namedtuple


def named_tuple(name, description='', **kwargs):
    """
    A named tuple with docstring documentation of each of its parameters
    :param str name: The named tuple's name
    :param str description: The named tuple's description
    :param kwargs: This named tuple's parameters' data with two different ways to describe said parameters. Format:
        <pre>{
            str: ( # The parameter's name
                str, # The parameter's type
                str # The parameter's description
            ),
            str: str, # The parameter's name: the parameter's description
            ... # Any other parameters
        }</pre>
    :return: collections.namedtuple
    """
    parameter_names = list(kwargs.keys())

    result = namedtuple(name, ' '.join(parameter_names))

    # If there are any parameters provided (such that this is not an empty named tuple)
    if len(parameter_names):
        # Add line spacing before describing this named tuple's parameters
        if description is not '':
            description += "\n"

        # Go through each parameter provided and add it to the named tuple's docstring description
        for parameter_name in parameter_names:
            parameter_data = kwargs[parameter_name]

            # Determine whether parameter type is included along with the description or
            # if only a description was provided
            parameter_type = ''
            if isinstance(parameter_data, str):
                parameter_description = parameter_data
            else:
                parameter_type, parameter_description = parameter_data

            description += "\n:param {type}{name}: {description}".format(
                type=parameter_type + ' ' if parameter_type else '',
                name=parameter_name,
                description=parameter_description
            )

            # Change the docstring specific to this parameter
            getattr(result, parameter_name).__doc__ = parameter_description

    # Set the docstring description for the resulting named tuple
    result.__doc__ = description

    return result

You can then create a new named tuple:

MyTuple = named_tuple(
    "MyTuple",
    "My named tuple for x,y coordinates",
    x="The x value",
    y="The y value"
)

Then instantiate the described named tuple with your own data, ie.

t = MyTuple(4, 8)
print(t) # prints: MyTuple(x=4, y=8)

When executing help(MyTuple) via the python3 command line the following is shown:

Help on class MyTuple:

class MyTuple(builtins.tuple)
 |  MyTuple(x, y)
 |
 |  My named tuple for x,y coordinates
 |
 |  :param x: The x value
 |  :param y: The y value
 |
 |  Method resolution order:
 |      MyTuple
 |      builtins.tuple
 |      builtins.object
 |
 |  Methods defined here:
 |
 |  __getnewargs__(self)
 |      Return self as a plain tuple.  Used by copy and pickle.
 |
 |  __repr__(self)
 |      Return a nicely formatted representation string
 |
 |  _asdict(self)
 |      Return a new OrderedDict which maps field names to their values.
 |
 |  _replace(_self, **kwds)
 |      Return a new MyTuple object replacing specified fields with new values
 |
 |  ----------------------------------------------------------------------
 |  Class methods defined here:
 |
 |  _make(iterable) from builtins.type
 |      Make a new MyTuple object from a sequence or iterable
 |
 |  ----------------------------------------------------------------------
 |  Static methods defined here:
 |
 |  __new__(_cls, x, y)
 |      Create new instance of MyTuple(x, y)
 |
 |  ----------------------------------------------------------------------
 |  Data descriptors defined here:
 |
 |  x
 |      The x value
 |
 |  y
 |      The y value
 |
 |  ----------------------------------------------------------------------
 |  Data and other attributes defined here:
 |  
 |  _fields = ('x', 'y')
 |  
 |  _fields_defaults = {}
 |  
 |  ----------------------------------------------------------------------
 |  Methods inherited from builtins.tuple:
 |  
 |  __add__(self, value, /)
 |      Return self+value.
 |  
 |  __contains__(self, key, /)
 |      Return key in self.
 |  
 |  __eq__(self, value, /)
 |      Return self==value.
 |  
 |  __ge__(self, value, /)
 |      Return self>=value.
 |  
 |  __getattribute__(self, name, /)
 |      Return getattr(self, name).
 |  
 |  __getitem__(self, key, /)
 |      Return self[key].
 |  
 |  __gt__(self, value, /)
 |      Return self>value.
 |  
 |  __hash__(self, /)
 |      Return hash(self).
 |  
 |  __iter__(self, /)
 |      Implement iter(self).
 |  
 |  __le__(self, value, /)
 |      Return self<=value.
 |  
 |  __len__(self, /)
 |      Return len(self).
 |  
 |  __lt__(self, value, /)
 |      Return self<value.
 |  
 |  __mul__(self, value, /)
 |      Return self*value.
 |  
 |  __ne__(self, value, /)
 |      Return self!=value.
 |  
 |  __rmul__(self, value, /)
 |      Return value*self.
 |  
 |  count(self, value, /)
 |      Return number of occurrences of value.
 |  
 |  index(self, value, start=0, stop=9223372036854775807, /)
 |      Return first index of value.
 |      
 |      Raises ValueError if the value is not present.

Alternatively, you can also specify the parameter's type via:

MyTuple = named_tuple(
    "MyTuple",
    "My named tuple for x,y coordinates",
    x=("int", "The x value"),
    y=("int", "The y value")
)

Answer 5

No, you can only add doc strings to modules, classes and function (including methods)

Answer 6

No need to use a wrapper class as suggested by the accepted answer. Simply literally add a docstring:

from collections import namedtuple

Point = namedtuple("Point", ["x", "y"])
Point.__doc__="A point in 2D space"

This results in: (example using ipython3):

In [1]: Point?
Type:       type
String Form:<class '__main__.Point'>
Docstring:  A point in 2D space

In [2]: 

Voilà!