[Python-Dev] Best way to specify docstrings for member objects

[Raymond Hettinger]

I'm working on ways to make improve help() by giving docstrings to member objects.

One way to do it is to wait until after the class definition and then make individual, direct assignments to __doc__ attributes.This way widely the separates docstrings from their initial __slots__ definition.   Working downstream from the class definition feels awkward and doesn't look pretty.  

There's another way I would like to propose¹.  The __slots__ definition already works with any iterable including a dictionary (the dict values are ignored), so we could use the values for the  docstrings.   

This keeps all the relevant information in one place (much like we already do with property() objects).  This way already works, we just need a few lines in pydoc to check to see if a dict if present.  This way also looks pretty and doesn't feel awkward.

I've included worked out examples below.  What do you all think about the proposal?


Raymond


¹ https://bugs.python.org/issue36326


====== Desired help() output ======

>>> help(NormalDist)
Help on class NormalDist in module __main__:

class NormalDist(builtins.object)
 |  NormalDist(mu=0.0, sigma=1.0)
 |  
 |  Normal distribution of a random variable
 |  
 |  Methods defined here:
 |  
 |  __init__(self, mu=0.0, sigma=1.0)
 |      NormalDist where mu is the mean and sigma is the standard deviation.
 |  
 |  cdf(self, x)
 |      Cumulative distribution function.  P(X <= x)
 |  
 |  pdf(self, x)
 |      Probability density function.  P(x <= X < x+dx) / dx
 |  
 |  ----------------------------------------------------------------------
 |  Data descriptors defined here:
 |  
 |  mu
 |      Arithmetic mean.
 |  
 |  sigma
 |      Standard deviation.
 |  
 |  variance
 |      Square of the standard deviation.



====== Example of assigning docstrings after the class definition ======

class NormalDist:
    'Normal distribution of a random variable'

    __slots__ = ('mu', 'sigma')

    def __init__(self, mu=0.0, sigma=1.0):
        'NormalDist where mu is the mean and sigma is the standard deviation.'
        self.mu = mu
        self.sigma = sigma

    @property
    def variance(self):
        'Square of the standard deviation.'
        return self.sigma ** 2.

    def pdf(self, x):
        'Probability density function.  P(x <= X < x+dx) / dx'
        variance = self.variance
        return exp((x - self.mu)**2.0 / (-2.0*variance)) / sqrt(tau * variance)

    def cdf(self, x):
        'Cumulative distribution function.  P(X <= x)'
        return 0.5 * (1.0 + erf((x - self.mu) / (self.sigma * sqrt(2.0))))

NormalDist.mu.__doc__ = 'Arithmetic mean'
NormalDist.sigma.__doc__ = 'Standard deviation'



====== Example of assigning docstrings with a dict =====

class NormalDist:
    'Normal distribution of a random variable'

    __slots__ = {'mu' : 'Arithmetic mean.', 'sigma': 'Standard deviation.'}

    def __init__(self, mu=0.0, sigma=1.0):
        'NormalDist where mu is the mean and sigma is the standard deviation.'
        self.mu = mu
        self.sigma = sigma

    @property
    def variance(self):
        'Square of the standard deviation.'
        return self.sigma ** 2.

    def pdf(self, x):
        'Probability density function.  P(x <= X < x+dx) / dx'
        variance = self.variance
        return exp((x - self.mu)**2.0 / (-2.0*variance)) / sqrt(tau * variance)

    def cdf(self, x):
        'Cumulative distribution function.  P(X <= x)'
        return 0.5 * (1.0 + erf((x - self.mu) / (self.sigma * sqrt(2.0))))