# Copyright 2013, Rick "rantingrick" Johnson
#
# Permission to use, copy, modify, and distribute this software for
# any purpose and without fee is hereby granted, provided that the above
# copyright notice appear in all copies.
#
# THIS SOFTWARE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR
# IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
#-----------------------------------------------------------------------------
#
# This script needs to be loaded when Python starts. But since i'm
# not supplying an installer, you'll have to tell Python how to load
# it yourself. Which is not very difficult really.
#
# The easiest method to "auto-load" this script is to create a .pth
# file and save it somewhere that python can find it. If your a noob
# and don't know what that means, then just throw the .pth file in
# your PythonXY folder.
#
# The contents of the .pth file MUST include the following line:
#
# import C
#
# Noob Note: You can name the .pth file anything you want, but this
# module must be named C.py. Yes, with a capital C!
#
# Enjoy.
import sys as _sys
class ConstantDeletionError(Exception):
pass
class ConstantSyntaxError(Exception):
pass
class ConstantMutationError(Exception):
pass
class _Constants(object):
"""
DESIGN NOTES:
This object is meant to provide a namespace for true constant
variables in Python -- with no need to import anything!
A toplevel "constants" object is injected at runtime, and always
available within ANY Python module via the name "C". Note the
capital letter, it's significant!
I like constant variables to be qualified, but not behind a
long name, and only a single letter can fulfill both wishes.
I also wanted constants access to be noticeable in the source,
but not overwhelming! Hence the choice of capital "C" over
lowercase "c".
Those of you withJava background should be comfortable
with "C" due to your experiences with the "R" object.
PUBLIC METHODS:
add_namespace(str name)
get_path()
USAGE:
Assignment:
C.name = value
Query:
C.name
Expansion:
C.add_namespace(name)
"""
MUTATE_MSG = "Constants cannot be mutated once intitalized!"
DELETE_MSG = 'WARNING: The constant variable {0!r} was deleted!'
ACCESS_MSG = 'Access to private variable {0!r} is denied!'
def __init__(self, name):
self.__dict__["__private"] = {
"dirlst":[],
"name":name,
}
def __str__(self):
fmtstr1 = "{0}(\n{1}\n )"
fmtstr2 = "{0}(<empty>)"
lst = []
pDict = self.__dict__["__private"]
for name in pDict["dirlst"]:
value = self.__dict__[name]
lst.append( " {0} = {1!r}".format(name, value))
values = '\n'.join(lst)
if not values:
fmtstr1 = fmtstr2
return fmtstr1.format(pDict["name"], values)
def __dir__(self):
return self.__dict__["__private"]["dirlst"]
def __getattribute__(self, name):
## print "_Constants.__getattribute__({0!r})".format(name)
if name == "__private" :
# This only stops direct access!
raise Exception(self.ACCESS_MSG.format(name))
return object.__getattribute__(self, name)
def __setattr__(self, name, value):
## print "_Constants.__setattr__({0!r}, {1!r})".format(name, value)
if name in self.__dict__ and name != "__private":
# This only stops direct access!
raise ConstantMutationError(self.MUTATE_MSG.format(name))
else:
self.__dict__["__private"]["dirlst"].append(name.upper())
self.__dict__[name.upper()] = value
def __delattr__(self, name):
## print "_Constants.__delattr__({0!r})".format(name)
pDict = self.__dict__["__private"]
path = "{0}.{1}".format(pDict["name"], name)
if name == "__private":
raise Exception(self.ACCESS_MSG.format(path))
elif name in self.__dict__:
raise ConstantDeletionError()
def get_path(self):
return self.__dict__["__private"]["name"]
def add_namespace(self, name):
"""Add a new constants namespace named <name>"""
name = name.upper()
pDict = self.__dict__["__private"]
pDict["dirlst"].append(name)
newname = pDict["name"] + ".{0}".format(name)
self.__dict__[name] = _Constants(newname)
#
# Inject a toplevel instance of _Constants (named "C") into the
# builtins module namespace.
_sys.modules['__builtin__'].__dict__['C'] = _Constants("C")
if __name__ == '__main__':
print C
print '\nAdding constants to "C"'
C.str = ""
C.int = 1
C.float = 1.333
print C
print '\nMutating constants of "C"'
try:
C.STR = "XXX"
except ConstantMutationError:
pass
try:
C.INT = 10
except ConstantMutationError:
pass
try:
C.FLOAT = 5.333
except ConstantMutationError:
pass
print C
# Test for case sensitivity.
try:
C.int
except Exception:
pass
# Test for correct members.
for name in ("INT", "STR", "FLOAT"):
getattr(C, name)
assert len(dir(C)) == 3
print '\nDeleting constants of "C"'
try:
del C.INT
except ConstantDeletionError:
pass
try:
del C.STR
except ConstantDeletionError:
pass
try:
del C.FLOAT
except ConstantDeletionError:
pass
print C
print '\nAdding new space "C.math"'
C.add_namespace("math")
C.MATH.PI = 3.14
print C.MATH
--
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