Changeset 1919 for inundation/pyvolution/util.py

Timestamp:

Oct 14, 2005, 11:26:21 AM (19 years ago)

Author:

ole

Message:

Implemented arbitrary expressions for sww2dem using code from changeset:1916

File:

• inundation/pyvolution/util.py (modified) (1 diff)

inundation/pyvolution/util.py

@@ -457 +457 @@
     sww.store_timestep('stage')
 
+
+
+
+
+
+
+def apply_expression_to_dictionary(expression, _):
+    """Apply arbitrary expression to values of dictionary _
+
+    expression: Arbitrary, e.g. arithmetric, expression relating keys
+                from dictionary _. A key must not be the single character '_'
+
+    _: Dictionary of variable names used in expression and their
+       corresponding values. The dictinary name is chosen as the
+       inconspicuous symbol _ in order to avoid single letter variable
+       to inabvertently substitute parts of the dictionary name
+    
+
+    Given an expression in terms of the keys, replace key by the
+    corresponding values and evaluate.
+
+    Values in dictionary must support operators given in expression
+    e.g. by overloading
+    """
+
+    #FIXME: Varibles may substitute into other variables e.g. x into xmomentum.
+    
+    import types
+
+    assert isinstance(expression, basestring)
+    assert type(_) == types.DictType
+
+    #Replace key names with values
+    for key in _.keys():
+        msg = 'Key must not be the single character "_"'
+        assert key != '_', msg
+        expression = expression.replace(key,
+                                        '_["%s"]' %key)
+
+
+    #Evaluate and return
+    try:
+        return eval(expression)
+    except NameError, e:
+        msg = 'Expression "%s" could not be evaluated: %s' %(expression, e)
+        raise NameError, msg
+    
+
+
+
+
+
+
+
 ####################################################################
 #Python versions of function that are also implemented in util_gateway.c