replacing eval with ast parse

ihatemoney/forms.py

@@ -14,7 +14,7 @@ from jinja2 import Markup
 import email_validator
 
 from ihatemoney.models import Project, Person
-from ihatemoney.utils import slugify
+from ihatemoney.utils import slugify, eval_arithmetic_expression
 
 
 def get_billform_for(project, set_default=True, **kwargs):
@@ -54,15 +54,12 @@ class CalculatorStringField(StringField):
     def process_formdata(self, valuelist):
         if valuelist:
             error_msg = "Not a valid amount or expression"
-            value = str(valuelist[0]).replace(" ", "").replace(",", ".")
+            value = str(valuelist[0]).replace(",", ".")
 
             if not match(r'^[ 0-9\.\+\-\*/\(\)]{0,50}$', value) or "**" in value:
                 raise ValueError(error_msg)
 
-            try:
-                valuelist[0] = str(eval(value, {"__builtins__": None}, {}))
-            except (SyntaxError, NameError, TypeError, ZeroDivisionError):
-                raise ValueError(error_msg)
+            valuelist[0] = str(eval_arithmetic_expression(value))
 
         return super(CalculatorStringField, self).process_formdata(valuelist)
 

ihatemoney/tests/tests.py

@@ -1399,7 +1399,7 @@ class APITestCase(IhatemoneyTestCase):
             "(20 + 2",  # invalid expression
             "20/0",  # invalid calc
             "9999**99999999999999999",  # exponents
-            "2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2"  # greater than 50 chars
+            "2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2*2",  # greater than 50 chars,
         ]
 
         for amount in erroneous_amounts:

ihatemoney/utils.py

@@ -1,5 +1,7 @@
 import base64
 import re
+import ast
+import operator
 
 from io import BytesIO, StringIO
 import jinja2
@@ -206,3 +208,33 @@ 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