Wrap converts strings

docs/wrapping.rst

@@ -82,14 +82,16 @@ Or in the decorator format:
                 Use None to skip conversion of any given element.
     - **strict**: if `True` all convertible arguments must be a Quantity
                   and others will raise a ValueError (True by default)
+                  `strict` also enables implicit string conversion. If
+                  a string can be converted to a Quantity, it will be.
 
 
 
 Strict Mode
 -----------
 
 By default, the function is wrapped in `strict` mode. In this mode,
-the input arguments assigned to units must be a Quantities.
+the input arguments assigned to units must be Quantities.
 
 .. doctest::
 
@@ -100,6 +102,13 @@ the input arguments assigned to units must be a Quantities.
     ...
     ValueError: A wrapped function using strict=True requires quantity for all arguments with not None units. (error found for meter, 1.0)
 
+Strict mode also enables automatic conversion of strings into Quantities when possible.
+
+.. doctest::
+
+    >>> mypp('1 m')
+    <Quantity(2.0064092925890407, 'second')>
+
 To enable using non-Quantity numerical values, set strict to False`.
 
 .. doctest::

pint/registry_helpers.py

@@ -120,10 +120,19 @@ def _converter(ureg, values, strict):
                 new_values[ndx] = ureg._convert(values[ndx]._magnitude,
                                                 values[ndx]._units,
                                                 args_as_uc[ndx][0])
+
+            # If the input is a string and strict is active, convert it to a quantity.
+            elif string_types in type(values[ndx]).mro() and strict:
+                implicit_quantity = ureg.Quantity(values[ndx])
+                new_values[ndx] = ureg._convert(implicit_quantity._magnitude,
+                                                implicit_quantity._units,
+                                                args_as_uc[ndx][0])
+
+
             else:
                 if strict:
                     raise ValueError('A wrapped function using strict=True requires '
-                                     'quantity for all arguments with not None units. '
+                                     'quantity or string for all arguments with not None units. '
                                      '(error found for {}, {})'.format(args_as_uc[ndx][0], new_values[ndx]))
 
         return new_values, values_by_name
@@ -143,7 +152,7 @@ def _apply_defaults(func, args, kwargs):
         if param.name not in bound_arguments.arguments:
             bound_arguments.arguments[param.name] = param.default
     args = [bound_arguments.arguments[key] for key in sig.parameters.keys()]
-    return args, {} 
+    return args, {}
 
 def wraps(ureg, ret, args, strict=True):
     """Wraps a function to become pint-aware.
@@ -186,7 +195,7 @@ def decorator(func):
         def wrapper(*values, **kw):
 
             values, kw = _apply_defaults(func, values, kw)
-                
+
             # In principle, the values are used as is
             # When then extract the magnitudes when needed.
             new_values, values_by_name = converter(ureg, values, strict)

pint/testsuite/test_unit.py

@@ -343,6 +343,19 @@ def func(x):
         self.assertEqual(f3(3. * ureg.centimeter), 0.03 * ureg.centimeter)
         self.assertEqual(f3(3. * ureg.meter), 3. * ureg.centimeter)
 
+        # Test string conversion when strict=True.
+        f3 = ureg.wraps('centimeter', ['meter', ], strict=True)(func)
+        self.assertEqual(f3('3 cm'), .03 * ureg.centimeter)
+        self.assertEqual(f3('3 m'), 3. * ureg.centimeter)
+        # Test that string conversion also rejects incorrect units.
+        self.assertRaises(ValueError, f3, '3 s')
+
+        # Test that string conversion fails when strict=False
+        f3 = ureg.wraps('centimeter', ['meter', ], strict=False)(func)
+        # self.assertRaises(ValueError, f3, '3 cm')
+        self.assertEqual(f3('3 cm'), '3 cm' * ureg.centimeter)
+        # self.assertEqual(f3('3 m'), 3. * ureg.centimeter)
+
         def gfunc(x, y):
             return x + y