How do you create constants?

[Dale Strickland-Clark]

"Tom wright" <thomas.wright1 at ntlworld.REMOVETHIS.com> wrote:

>Hi All,
>
>I am a newbie to python, and I have the following question,
>
>in c++ I can create a constant through something like an enum, or a const
>variable or a static.  How do I go about doing something similar to this in
>python, e.g.
>
>I want to create a python file/class which contains all my constants for
>ease of use/maintenance.  I then wish to use these from various other
>files/classes.  Now I understand that due to the scoping of python
>variables, I can not simply reference variables in a separate module, but
>how can I achieve something similar to my global defines file as in c++, by
>the way, the defines would be constant strings and integers.
>
>I am sure there is an easy way to do this, but I havnt found it yet !!
>
>TIA for pointers
>
>Regards
>
>Tom
>
>PS I have RTFM, but if its there I have missed it
>

AFAIK, Python doesn't do constants, as such.

If you want to use 'set once' values, you could write a simple class
for that. Something like this:

class SetOnce:
	def __setattr__(self, key, value):
		if key in dir(self):
			raise ValueError(key)
		self.__dict__[key] = value
	

If you want sequential flag bits, I have found this handy:

# This class allocates flag bits sequentially.
class Flagbit:
	def __init__(self):
		self.bit = 1

	def flag(self):
		if self.bit == 0:
			raise Hell(12, 'FlagBit: Too many flag bits')
		rv = self.bit
		self.bit = self.bit << 1
		return rv


Hope that helps.
--
Dale Strickland-Clark
Out-Think Ltd
Business Technology Consultants