how to set global const variables in python

Question

I am building a solution with various classes and functions all of which need access to some global consants to be able to work appropriately. As there is no const in python, what would you consider best practice to set a kind of global consants.

global const g = 9.8 

So I am looking for a kind of the above

edit: How about:

class Const():
 @staticmethod
 def gravity():
 return 9.8
print 'gravity: ', Const.gravity()

?

• user2357112: Doesn't work. Anyone can change Const.gravity or just replace the Const class entirely. The lack of anything like const is a deliberate design decision; Python makes it very difficult to enforce that code won't touch something it shouldn't. Instead, if you're not supposed to touch something, standard practice is to just not touch it.

Answer 1

You cannot define constants in Python. If you find some sort of hack to do it, you would just confuse everyone.

To do that sort of thing, usually you should just have a module - globals.py for example that you import everywhere that you need it

• gen: I suspected "As there is no const in python" :/
• gen: how do you name your consts? all caps? or something like c_gravitation?
• kindall: PEP 8 says all caps with underscores.

Answer 2

General convention is to define variables with capital and underscores and not change it. Like,

GRAVITY = 9.8

However, it is possible to create constants in Python using namedtuple

import collections
Const = collections.namedtuple('Const', 'gravity pi')
const = Const(9.8, 3.14)
print(const.gravity) # => 9.8
# try to change, it gives error
const.gravity = 9.0 # => AttributeError: can't set attribute

For namedtuple, refer to docs here

• nehem: This is the closest implementation of const..