Hej All,
I started developing for sage not so long ago and I wonder if there
are some good coding practices / conventions for dealing with global
functions and attributes which have the same name and also do the same
thing. An example of such a global function / atribute combination:
sage: sqrt(3)
sqrt(3)
sage: 3.sqrt()
sqrt(3)
I came up with this question because during the developing I ran into
two examples showing the relevance of the question. (And the relevance
is also backed by my experience in using sage as an enduser. Global
functions sometimes doing something else as atributes, or the global
funtion working just fine and not having the local function and all
sort of related unexpected or non-intuitive behaviour)
Example 1: the valuation function.
def valuation(m, p):
if hasattr(m, 'valuation'):
return m.valuation(p)
if is_FractionFieldElement(m):
return valuation(m.numerator()) - valuation(m.denominator())
if m == 0:
import sage.rings.all
return sage.rings.all.infinity
r = 0
power = p
while not (m % power): # m % power == 0
r += 1
power *= p
return r
The first point is that It has some implementation specific for
FractionFieldElements in here of which I think this should not be
there (especially since fraction fields have a valuation method).
I already made a small trac ticket for this now needing review:
http://trac.sagemath.org/sage_trac/ticket/9652
And the second point is that there is code after:
if hasattr(m, 'valuation'):
return m.valuation(p)
I think the code after that should be put in the apropriate ring
element class. The second example shows why.
Example 2: A similar thing goes wrong with the is_square() method of
which I recently broke a doctest during developement by adding a
is_square() method to RingElement which raises a "NotImplementedError"
in most cases since I expect others to overwrite it. Instead of the
hasattr they do it by the "try: except AtributeError:" construction.
In arith.py there are about 20 cases in which things like one of the
examples above happen. And also in some cases similar things happen
using isinstance.
If things like that happen that often then there should be a reason
for that right? Is this part of sage design and am I not getting a
convention/coding style or is it for historic reasons?
In both cases I would like to know some best practices for dealing
with the problems involved in the "global functions versus atributes"
story. And maybe there should be a small part discussing this in the
developerguide in the "Design" or "Conventions for Coding in Sage".
Kind Regards
Maarten Derickx
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