1 files changed, 196 insertions, 0 deletions
diff --git a/grc/core/expr_utils.py b/grc/core/expr_utils.py
new file mode 100644
index 0000000000..66911757d6
--- /dev/null
+++ b/grc/core/expr_utils.py
@@ -0,0 +1,196 @@
+"""
+Copyright 2008-2011 Free Software Foundation, Inc.
+This file is part of GNU Radio
+
+GNU Radio Companion is free software; you can redistribute it and/or
+modify it under the terms of the GNU General Public License
+as published by the Free Software Foundation; either version 2
+of the License, or (at your option) any later version.
+
+GNU Radio Companion is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
+"""
+
+import string
+VAR_CHARS = string.letters + string.digits + '_'
+
+
+class graph(object):
+    """
+    Simple graph structure held in a dictionary.
+    """
+
+    def __init__(self): self._graph = dict()
+
+    def __str__(self): return str(self._graph)
+
+    def add_node(self, node_key):
+        if node_key in self._graph:
+            return
+        self._graph[node_key] = set()
+
+    def remove_node(self, node_key):
+        if node_key not in self._graph:
+            return
+        for edges in self._graph.values():
+            if node_key in edges:
+                edges.remove(node_key)
+        self._graph.pop(node_key)
+
+    def add_edge(self, src_node_key, dest_node_key):
+        self._graph[src_node_key].add(dest_node_key)
+
+    def remove_edge(self, src_node_key, dest_node_key):
+        self._graph[src_node_key].remove(dest_node_key)
+
+    def get_nodes(self):
+        return self._graph.keys()
+
+    def get_edges(self, node_key):
+        return self._graph[node_key]
+
+
+def expr_split(expr):
+    """
+    Split up an expression by non alphanumeric characters, including underscore.
+    Leave strings in-tact.
+    #TODO ignore escaped quotes, use raw strings.
+
+    Args:
+        expr: an expression string
+
+    Returns:
+        a list of string tokens that form expr
+    """
+    toks = list()
+    tok = ''
+    quote = ''
+    for char in expr:
+        if quote or char in VAR_CHARS:
+            if char == quote:
+                quote = ''
+            tok += char
+        elif char in ("'", '"'):
+            toks.append(tok)
+            tok = char
+            quote = char
+        else:
+            toks.append(tok)
+            toks.append(char)
+            tok = ''
+    toks.append(tok)
+    return filter(lambda t: t, toks)
+
+
+def expr_replace(expr, replace_dict):
+    """
+    Search for vars in the expression and add the prepend.
+
+    Args:
+        expr: an expression string
+        replace_dict: a dict of find:replace
+
+    Returns:
+        a new expression with the prepend
+    """
+    expr_splits = expr_split(expr)
+    for i, es in enumerate(expr_splits):
+        if es in replace_dict.keys():
+            expr_splits[i] = replace_dict[es]
+    return ''.join(expr_splits)
+
+
+def get_variable_dependencies(expr, vars):
+    """
+    Return a set of variables used in this expression.
+
+    Args:
+        expr: an expression string
+        vars: a list of variable names
+
+    Returns:
+        a subset of vars used in the expression
+    """
+    expr_toks = expr_split(expr)
+    return set(filter(lambda v: v in expr_toks, vars))
+
+
+def get_graph(exprs):
+    """
+    Get a graph representing the variable dependencies
+
+    Args:
+        exprs: a mapping of variable name to expression
+
+    Returns:
+        a graph of variable deps
+    """
+    vars = exprs.keys()
+    # Get dependencies for each expression, load into graph
+    var_graph = graph()
+    for var in vars:
+        var_graph.add_node(var)
+    for var, expr in exprs.iteritems():
+        for dep in get_variable_dependencies(expr, vars):
+            if dep != var:
+                var_graph.add_edge(dep, var)
+    return var_graph
+
+
+def sort_variables(exprs):
+    """
+    Get a list of variables in order of dependencies.
+
+    Args:
+        exprs: a mapping of variable name to expression
+
+    Returns:
+        a list of variable names
+    @throws Exception circular dependencies
+    """
+    var_graph = get_graph(exprs)
+    sorted_vars = list()
+    # Determine dependency order
+    while var_graph.get_nodes():
+        # Get a list of nodes with no edges
+        indep_vars = filter(lambda var: not var_graph.get_edges(var), var_graph.get_nodes())
+        if not indep_vars:
+            raise Exception('circular dependency caught in sort_variables')
+        # Add the indep vars to the end of the list
+        sorted_vars.extend(sorted(indep_vars))
+        # Remove each edge-less node from the graph
+        for var in indep_vars:
+            var_graph.remove_node(var)
+    return reversed(sorted_vars)
+
+
+def sort_objects(objects, get_id, get_expr):
+    """
+    Sort a list of objects according to their expressions.
+
+    Args:
+        objects: the list of objects to sort
+        get_id: the function to extract an id from the object
+        get_expr: the function to extract an expression from the object
+
+    Returns:
+        a list of sorted objects
+    """
+    id2obj = dict([(get_id(obj), obj) for obj in objects])
+    # Map obj id to expression code
+    id2expr = dict([(get_id(obj), get_expr(obj)) for obj in objects])
+    # Sort according to dependency
+    sorted_ids = sort_variables(id2expr)
+    # Return list of sorted objects
+    return [id2obj[id] for id in sorted_ids]
+
+
+if __name__ == '__main__':
+    for i in sort_variables({'x': '1', 'y': 'x+1', 'a': 'x+y', 'b': 'y+1', 'c': 'a+b+x+y'}):
+        print i