On one the many mini-reports we use, we have a bunch of counts that are
frequently zero; because the other counts can also be low, it becomes
easy to miss the non-zero counts. For example:
Code Description
Conv Errors : 6
31,N DPV Failure : 4
10: Invalid Address : 0
11: Invalid C/S/Z : 0
12: Invalid State : 0
13: Invalid City : 0
17: Insufficient Information : 0
33: Non-Deliverable : 0
98: Non-USPS zip : 0
21: Address Not Found : 0
22: Multiple Responses : 3
23: Error in Primary : 0
24: Error in Secondary : 0
So I thought I would print '-' instead...
Code Description
Conv Errors : 6
31,N DPV Failure : 4
10: Invalid Address : -
11: Invalid C/S/Z : -
12: Invalid State : -
13: Invalid City : -
17: Insufficient Information : -
33: Non-Deliverable : -
98: Non-USPS zip : -
21: Address Not Found : -
22: Multiple Responses : 3
23: Error in Primary : -
24: Error in Secondary : -
Much easier to pick out the numbers now. To support this, the code
changed slightly -- it went from
'%-25s: %7d' % ('DPV Failure', counts['D'])
to
'%-25s: %7s' % ('DPV Failure', counts['D'] if counts['D'] else '-'))
This became a pain after a dozen lines, prompting my previous question
about the difference between %s and %d when printing integers. With the
excellent replies I received I coded a short class:
class DashInt(int):
def __str__(x):
if x:
return str(x)
return '-'
and my line printing code shrunk back to it's previous size. Well, it
wasn't long before I realized that when a DashInt was added to an int,
an int came back... and so did the '0's. So I added some more lines to
the class.
def __add__(x, other):
result = super(DashInt, x).__add__(other)
return result
and then I tried to do a floating type operation, so added yet more lines...
def __add__(x, other):
result = super(DashInt, x).__add__(other)
if result == NotImplemented:
return NotImplemented
return result
and so on and so on for the basic math functions that I will be using...
what a pain! And then I had a thought... metaclasses! If DashInt used
a metaclass that would automatically check the result, and if it was
base class wrap it up in the new subclass, my DashInt class could go
back to being five simple lines, plus one more for the metaclass specifier.
So DashInt currently looks like this:
class TempInt(int):
__metaclass__ = Perpetuate
def __str__(x):
if x == 0:
return '-'
return int.__str__(x)
and Perpetuate looks like this:
class Perpetuate(type):
def __init__(yo, *args, **kwargs):
super(type, yo).__init__(*args)
def __new__(metacls, cls_name, cls_bases, cls_dict):
if len(cls_bases) > 1:
raise TypeError("multiple bases not allowed")
result_class = type.__new__( \
metacls, cls_name, cls_bases, cls_dict)
base_class = cls_bases[0]
known_methods = set()
for method in cls_dict.keys():
if callable(getattr(result_class, method)):
known_methods.add(method)
base_methods = set()
for method in base_class.__dict__.keys():
if callable(getattr(base_class, method, None)) and \
method not in ('__new__'):
base_methods.add(method)
for method in base_methods:
if method not in known_methods:
setattr(result_class, method, \
_wrap(base_class, getattr(base_class, method)))
return result_class
def _wrap(base, code):
def wrapper(self, *args, **kwargs):
result = code(self, *args, **kwargs)
if type(result) == base:
return self.__class__(result)
return result
wrapper.__name__ = code.__name__
wrapper.__doc__ = code.__doc__
return wrapper
It seems to work fine for normal operations. I had to exclude __new__
because it was a classmethod, and I suspect I would have similar issues
with staticmethods.
Any comments appreciated, especially ideas on how to better handle
class- and staticmethods
~Ethan~
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