Add option of returning None on failure

pylintrc

@@ -61,7 +61,7 @@ evaluation=10.0 - ((float(5 * error + warning + refactor + convention) / stateme
 # --enable=similarities". If you want to run only the classes checker, but have
 # no Warning level messages displayed, use"--disable=all --enable=classes
 # --disable=W"
-disable=invalid-name,bad-continuation,too-many-arguments,too-many-locals,too-many-statements,redefined-builtin
+disable=invalid-name,bad-continuation,too-many-arguments,too-many-locals,too-many-statements,redefined-builtin,no-else-return
 
 
 [SIMILARITIES]

stringtopy/__init__.py

@@ -19,30 +19,42 @@
 BOOLEAN_FALSE = {'0', 'no', 'false', 'off', }
 
 
-def str_to_float_converter():
+def str_to_float_converter(use_none_on_fail=False):
     """
-    Returns a human friendly float converter, currently takes no arguments.
+    Returns a human friendly float converter, can use use_none_on_fail to
+    return None if value cannot be converted.
     """
     def str_to_float(s):
         """
         Convert a string to a float
         """
-        return float(Fraction(s))
+        try:
+            return float(Fraction(s))
+        except ValueError:
+            if use_none_on_fail:
+                return None
+            raise
     return str_to_float
 
 
-def str_to_int_converter():
+def str_to_int_converter(use_none_on_fail=False):
     """
-    Returns a human friendly int converter, currently takes no arguments.
+    Returns a human friendly int converter, can use use_none_on_fail to return
+    None if value cannot be converted.
     """
     def str_to_int(s):
         """
         Convert a string to a int
         """
-        frac = Fraction(s)
-        if frac.denominator == 1:
-            return int(frac)
-        raise ValueError("{} is not an integer".format(frac))
+        try:
+            frac = Fraction(s)
+            if frac.denominator == 1:
+                return int(frac)
+            raise ValueError("{} is not an integer".format(frac))
+        except ValueError:
+            if use_none_on_fail:
+                return None
+            raise
     return str_to_int
 
 
@@ -79,6 +91,9 @@ def str_to_bool_converter(
         )
 
     def str_to_bool(s):
+        """
+        Convert a string to a bool, based on settings
+        """
         s = s.strip().lower()
         if s in boolean_true:
             return True

tests/test_float.py

@@ -1,12 +1,17 @@
 from __future__ import division
 import pytest
 
+from stringtopy import str_to_float_converter
 
 
 def test_not_float(default_str_to_float):
     with pytest.raises(ValueError):
         default_str_to_float("this is not a float")
 
+def test_not_float_with_none():
+    str_to_float = str_to_float_converter(use_none_on_fail=True)
+    assert str_to_float("this is not a float") is None
+
 def test_decimal(default_str_to_float):
     assert 1.234 == default_str_to_float("1.234")