Set Decimal precision of default context from environment variable

This is placed in the trytond __init__.py because the default context must be
set prior to any start of thread. And thus it can only be set via environment.

Closes #13572

trytond/CHANGELOG

@@ -1,3 +1,4 @@
+* Set Decimal precision of default context from TRYTOND_DECIMAL_PREC
 * Replace usage of docstring of Model by __string__ attribute
 * Rename ir.model.field 'field_description' into 'string'
 * Replace docstring of models by __string__

trytond/trytond/__init__.py

@@ -1,5 +1,7 @@
 # This file is part of Tryton.  The COPYRIGHT file at the top level of
 # this repository contains the full copyright notices and license terms.
+
+import decimal
 import os
 import time
 import warnings
@@ -40,3 +42,5 @@ def default_user_agent(name="Tryton"):
 
 if requests_utils:
     requests_utils.default_user_agent = default_user_agent
+
+decimal.DefaultContext.prec = int(os.environ.get('TRYTOND_DECIMAL_PREC', 28))

trytond/trytond/commandline.py

@@ -65,6 +65,9 @@ def get_parser():
     parser.add_argument(
         "--logconf", dest="logconf", default=logging_config, metavar='FILE',
         help="set logging configuration file (ConfigParser format)")
+    parser.epilog = (
+        "The default Decimal precision can be specified in the "
+        "TRYTOND_DECIMAL_PREC environment variable.")
 
     return parser