On 25/11/2010 09:34, Glenn Linderman wrote:
So the following code defines constants with associated names that get
put in the repr.
I'm still a Python newbie in some areas, particularly classes and
metaclasses, maybe more.
But this Python 3 code seems to create constants with names ... works
for int and str at least.
Special case for int defines a special __or__ operator to OR both the
values and the names, which some might like.
Dunno why it doesn't work for dict, and it is too late to research
that today. That's the last test case in the code below, so you can
see how it works for int and string before it bombs.
There's some obvious cleanup work to be done, and it would be nice to
make the names actually be constant... but they do lose their .name if
you ignorantly assign the base type, so at least it is hard to change
the value and keep the associated .name that gets reported by repr,
which might reduce some confusion at debug time.
An idea I had, but have no idea how to implement, is that it might be
nice to say:
with imported_constants_from_module:
do_stuff
where do_stuff could reference the constants without qualifying them
by module. Of course, if you knew it was just a module of constants,
you could "import * from module" :) But the idea of with is that
they'd go away at the end of that scope.
Some techniques here came from Raymond's namedtuple code.
def constant( name, val ):
typ = str( type( val ))
if typ.startswith("<class '") and typ[ -2: ] == "'>":
typ = typ[ 8:-2 ]
ev = '''
class constant_%s( %s ):
def __new__( cls, val, name ):
self = %s.__new__( cls, val )
self.name = name
return self
def __repr__( self ):
return self.name + ': ' + str( self )
'''
if typ == 'int':
ev += '''
def __or__( self, other ):
if isinstance( other, constant_int ):
return constant_int( int( self ) | int( other ),
self.name + ' | ' + other.name )
'''
Not quite correct. If you or a value you with itself you should get back
just the value not something with "name|name" as the repr.
We can hold off on implementations until we have general agreement that
some kind of named constant *should* be added, and what the feature set
should look like.
All the best,
Michael
ev += '''
%s = constant_%s( %s, '%s' )
'''
ev = ev % ( typ, typ, typ, name, typ, repr( val ), name )
print( ev )
exec( ev, globals())
constant('O_RANDOM', val=16 )
constant('O_SEQUENTIAL', val=32 )
constant("O_STRING", val="string")
def foo( x ):
print( str( x ))
print( repr( x ))
print( type( x ))
foo( O_RANDOM )
foo( O_SEQUENTIAL )
foo( O_STRING )
zz = O_RANDOM | O_SEQUENTIAL
foo( zz )
y = {'ab': 2, 'yz': 3 }
constant('O_DICT', y )
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