From 04adfe4155e1bb37609edfe78ae67b361f51e0cf Mon Sep 17 00:00:00 2001
From: Byron Ullauri <Ullauri.Byron@gmail.com>
Date: Thu, 3 Jan 2019 04:03:13 -0500
Subject: Provide basic math operations on bills (#413)

* allow basic math ops in amount field for bills form
* docs: changing compile-translations to build-translations
---
 ihatemoney/utils.py | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

(limited to 'ihatemoney/utils.py')

diff --git a/ihatemoney/utils.py b/ihatemoney/utils.py
index ec22834..2fac4ef 100644
--- a/ihatemoney/utils.py
+++ b/ihatemoney/utils.py
@@ -1,5 +1,8 @@
+from __future__ import division
 import base64
 import re
+import ast
+import operator
 
 from io import BytesIO, StringIO
 import jinja2
@@ -206,3 +209,33 @@ class IhmJSONEncoder(JSONEncoder):
             except ImportError:
                 pass
             return JSONEncoder.default(self, o)
+
+
+def eval_arithmetic_expression(expr):
+    def _eval(node):
+        # supported operators
+        operators = {
+            ast.Add: operator.add,
+            ast.Sub: operator.sub,
+            ast.Mult: operator.mul,
+            ast.Div: operator.truediv,
+            ast.USub: operator.neg,
+        }
+
+        if isinstance(node, ast.Num):  # <number>
+            return node.n
+        elif isinstance(node, ast.BinOp):  # <left> <operator> <right>
+            return operators[type(node.op)](_eval(node.left), _eval(node.right))
+        elif isinstance(node, ast.UnaryOp):  # <operator> <operand> e.g., -1
+            return operators[type(node.op)](_eval(node.operand))
+        else:
+            raise TypeError(node)
+
+    expr = str(expr)
+
+    try:
+        result = _eval(ast.parse(expr, mode='eval').body)
+    except (SyntaxError, TypeError, ZeroDivisionError, KeyError):
+        raise ValueError("Error evaluating expression: {}".format(expr))
+
+    return result
-- 
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