naming of physical quantities in python

问题

I would like to establish a good naming scheme for physical/mathematical quantities used in my simulation code. Consider the following example:

from math import *

class GaussianBeamIntensity(object):
    """
    Optical intensity profile of a Gaussian laser beam.
    """

    def __init__(self, intensity_at_waist_center, waist_radius, wavelength):
        """
        Arguments:

        *intensity_at_waist_center*: The optical intensity of the beam at the
            center of its waist in W/m^2 units.

        *waist_radius*: The radius of the beam waist in meters.

        *wavelength*: The wavelength of the laser beam in meters.

        """

        self.intensity_at_waist_center = intensity_at_waist_center
        self.waist_radius = waist_radius
        self.wavelength = wavelength
        self._calculate_auxiliary_quantities()

    def _calculate_auxiliary_quantities(self):
        # Shorthand notation
        w_0, lambda_ = self.waist_radius, self.wavelength

        self.rayleigh_range = pi * w_0**2 / lambda_
        # Generally some more quantities could follow

    def __call__(self, rho, z):
        """
        Arguments:

        *rho*, *z*: Cylindrical coordinates of a spatial point.
        """
        # Shorthand notation
        I_0, w_0 = self.intensity_at_waist_center, self.waist_radius
        z_R = self.rayleigh_range

        w_z = w_0 * sqrt(1.0 + (z / z_R)**2)
        I = I_0 * (w_0 / w_z)**2 * exp(-2.0 * rho**2 / w_z**2)
        return I

What consistent naming scheme would you propose for the physical properties (properties, function arguments etc.) in order to balance between readability and concise notation (that formulae remain relatively short)? Could you please refine the example above? Or perhaps propose a better scheme?

It would be nice to follow the guidelines of PEP8, remembering that "A Foolish Consistency is the Hobgoblin of Little Minds". It seems difficult to stick to descriptive names while obeying the traditional 80-character limit for line lengths.

Thank you in advance!

回答1:

I think you've already found the good balance. Expressive names are important, so I totally agree with the use of wavelenght instead of lambda as a class attribute. This way the interface remains clear and expressive.

In a long formula, though, lambda_ is good choice as shorthand notation, because this is a commonly accepted and widely used notation for the wavelength in optics. I think when you implement a formula, what you want to do is staying as close as possible to the form of the equations you'd write on a piece of paper (or as they appear in an article etc).

In short: keep the interfaces expressive, the formulae short.

回答2:

Use Python3 and you can use the actual symbol λ for a variable name.

I look forward to writing code like:

from math import pi as π

sphere_volume = lambda r : 4/3 * π * r**3

来源：https://stackoverflow.com/questions/4227503/naming-of-physical-quantities-in-python