Importing a long list of constants to a Python file

Question

In Python  is there an analogue of the C preprocessor statement such as     define MY CONSTANT 50  Also  I have a large list of constants I d like to import to several classes  Is there an analogue of declaring the constants as a long sequence of statements like the above in a  py file and importing it to another  py file   Edit   The file Constants py reads      usr bin env python   encoding  utf-8     Constants py      MY CONSTANT ONE   50 MY CONSTANT TWO   51   And myExample py reads      usr bin env python   encoding  utf-8     myExample py      import sys import os  import Constants  class myExample      def   init   self           self someValueOne   Constants MY CONSTANT ONE   1         self someValueTwo   Constants MY CONSTANT TWO   1  if   name         main         x   MyClass     Edit   From the compiler      NameError   global name    MY CONSTANT ONE  is not defined       function init in myExample at line   13 self someValueOne     Constants MY CONSTANT ONE   1 copy   output Program exited with code  1   after 0 06 seconds

User · Answer

Sure  you can put your constants into a separate module  For example   const py   A   12 B    abc  C   1 2   main py   import const  print const A  const B  const C   Note that as declared above  A  B and C are variables  i e  can be changed at run time

User · Answer

If you really want constants  not just variables looking like constants  the standard way to do it is to use immutable dictionaries  Unfortunately it s not built-in yet  so you have to use third party recipes  like this one or that one

User · Answer

create constant file with any name like my constants py declare constant like that  CONSTANT NAME    SOME VALUE    For accessing constant in your code import file like that  import my constants as constant   and access the constant value as -  constant CONSTANT NAME

User · Answer

And ofcourse you can do     a py MY CONSTANT          b py from a import   print MY CONSTANT

User · Answer

Python isn t preprocessed  You can just create a file myconstants py   MY CONSTANT   50   And importing them will just work   import myconstants print myconstants MY CONSTANT   2

User · Answer

As an alternative to using the import approach described in several answers  have a look a the configparser module   The ConfigParser class implements a basic configuration file parser language which provides a structure similar to what you would find on Microsoft Windows INI files  You can use this to write Python programs which can be customized by end users easily

User · Answer

Try to look Create constants using a  quot settings quot  module  and Can I prevent modifying an object in Python   Another one useful link  http   code activestate com recipes 65207-constants-in-python  tells us about the following option   from copy import deepcopy  class const object        def   setattr   self  name  value           if self   dict   has key name               print  NO WAY this is a const    put here anything you want throw exc and etc              return deepcopy self   dict   name           self   dict   name    value      def   getattr   self  name  value           if self   dict   has key name               return deepcopy self   dict   name        def   delattr   self  item           if self   dict   has key item               print  NOOOOO    throw exception if needed  CONST   const   CONST Constant1   111 CONST Constant1   12 print a Constant1   111 CONST Constant2    tst  CONST Constant2    tst1  print a Constant2    tst    So you could create a class like this and then import it from you contants py module  This will allow you to be sure that value would not be changed  deleted

User · Answer

Python doesn t have a preprocessor  nor does it have constants in the sense that they can t be changed - you can always change  nearly  you can emulate constant object properties  but doing this for the sake of constant-ness is rarely done and not considered useful  everything  When defining a constant  we define a name that s upper-case-with-underscores and call it a day -  We re all consenting adults here   no sane man would change a constant  Unless of course he has very good reasons and knows exactly what he s doing  in which case you can t  and propably shouldn t  stop him either way   But of course you can define a module-level name with a value and use it in another module  This isn t specific to constants or anything  read up on the module system     a py MY CONSTANT          b py import a print a MY CONSTANT

[python] Importing a long list of constants to a Python file

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