Relation module has SQL-like delete

git-svn-id: http://galileo.dmi.unict.it/svn/relational/trunk@75 014f5005-505e-4b48-8d0a-63407b615a7c

CHANGELOG

@@ -51,3 +51,4 @@
 - New default relation's format is csv, as defined in RFC4180
 - Converted sample's relations to csv
 - Deb postinstall generates optimized files, this will increase loading speed
+- Relation module has SQL-like delete

relation.py

@@ -418,6 +418,27 @@ class relation (object):
             
         return res
 
+    def delete(self,expr):
+        '''Delete, expr must be a valid boolean expression, can contain field names,
+        constant, math operations and boolean ones.
+        This operation will change the relation itself instead of generating a new one,
+        deleting all the touples that make expr true.'''
+        attributes={}
+        new_content=[] #New content of the relation
+        for i in self.content:
+            for j in range(len(self.header.attributes)):
+                if i[j].isdigit():
+                    attributes[self.header.attributes[j]]=int(i[j])
+                elif rstring(i[j]).isFloat():
+                    attributes[self.header.attributes[j]]=float(i[j])
+                elif isDate(i[j]):
+                    attributes[self.header.attributes[j]]=rdate(i[j])
+                else:
+                    attributes[self.header.attributes[j]]=i[j]
+            if not eval(expr,attributes):
+                new_content.append(i)
+        self.content=new_content
+    
 class header (object):
     '''This class defines the header of a relation.
     It is used within relations to know if requested operations are accepted'''