This program runs through a preprocessed makefile (make --print-data-base | python make_graph.py [options]) to assemble a directed graph of its variables. I originally put together the program to visualize assignment redundancies in a particularly messy build, but I haven’t used it much since. I’ve used it on fairly large builds and haven’t experienced any particular performance issues, although I’m sure it can be improved in that regard.

I’d love to know what I can do to improve the program. In particular I’d like to make sure it’s somewhat pythonic.

import argparse import graphviz import re import subprocess import sys import unittest  def all_assignments(database):     assignments = {}      # accept target-specific variables     re_assignment = re.compile(r'.*?([^:#= ]+) :?= .*$  ')     re_variable = re.compile(r'$  \(([^:#= ]+?)\)')     for line in database:         if not any(assign in line for assign in (' = ', ' := ')):             continue          match_assignee = re_assignment.match(line)         if not match_assignee:             continue          assignee = match_assignee.group(1)         assignments.setdefault(assignee, set())         for match_variable in re.finditer(re_variable, line):             assignments[assignee].add(match_variable.group(1))      return assignments  def without_edges(assignments):    # not assigned other variables     singles = {assignee for (assignee, variables) in                assignments.iteritems() if len(variables) == 0}     # and not assigned to another variables     for (_, variables) in assignments.iteritems():         singles.difference_update(variables)      return singles  def trim(assignments, vars_to_trim):     for var in vars_to_trim:         assignments.pop(var, None)     return assignments  # Alternatively, can be acquired using make --print-data-base -f /dev/null echo_internal = """ echo:     @echo $  (subst <,\<,$  (.VARIABLES)) """  # on my system, <D is the first variable  def internal_variables():     variables = subprocess.check_output(['make', '--eval', echo_internal])     return set(variables.split())  def graph_assignments(assignments, include_internal):     qualifying_assignments = trim(assignments,                                   set(without_edges(assignments)))     return (qualifying_assignments if include_internal else             trim(qualifying_assignments, internal_variables()))  def nodes(assignments):     nodes = {assignee for (assignee, _) in assignments.iteritems()}     for (_, variables) in assignments.iteritems():         nodes.update(variables)     return nodes  class TestAssignments(unittest.TestCase):     # This particular edge wouldn't appear from --print-data-base     # output, since GNU Make would expand the variable immediately     def test_immediate(self):         s = ('A := a\n'              'B := $  (A)\n')         self.assertEqual(all_assignments(s.splitlines()),                          {'A' : set(),                           'B' : {'A'}})      def test_deferred(self):         s = ('A = a\n'              'B = $  (A)\n')         self.assertEqual(all_assignments(s.splitlines()),                          {'A' : set(),                           'B' : {'A'}})      def test_empty(self):         self.assertEqual(all_assignments('B = $  (A)\n'.splitlines()),                          {'B' : {'A'}})      def test_multiple(self):         self.assertEqual(all_assignments('A = $  (B)$  (C) $  (D)\n'.splitlines()),                          {'A' : {'B', 'C', 'D'}})      def test_without_edges(self):         self.assertEqual(without_edges({'A' : set(),                                         'B' : {'A'},                                         'C' : set()}), {'C'})      def test_nodes(self):         self.assertEqual(nodes({'A' : set(),                                 'B' : {'A'},                                 'C' : set()}), {'A', 'B', 'C'})  def add_nodes(dot, nodes):     for node in nodes:         dot.node(node)  def add_edges(dot, assignments):     for (assignee, variables) in assignments.iteritems():         for variable in variables:             dot.edge(assignee, variable)  def output_graph(assignments, graph_name, view):     dot = graphviz.Digraph(comment = 'GNU Make Variable Directional Graph')      add_nodes(dot, nodes(assignments))     add_edges(dot, assignments)      dot.render(graph_name, view = view)  def output_text(assignments):     for (assignee, variables) in sorted(assignments.iteritems()):         sys.stdout.write('%s = %s\n' % (assignee, ' '.join(sorted(variables))))  def make_graph(database, graph_name, as_text, include_internal, view):     assignments = graph_assignments(all_assignments(database), include_internal)     if as_text:         output_text(assignments)     else:         output_graph(assignments, graph_name, view)  if __name__ == "__main__":     parser = argparse.ArgumentParser(__file__)     parser.add_argument('--database', type = argparse.FileType('r'),                         help = ("GNU Make database filename; if no filename is"                                 " provided the database is expected on the"                                 " standard input stream"))     parser.add_argument('--graph-name', default = 'graph', dest = 'graph_name',                         help = ("Graph name; defaults to 'graph'"))     parser.add_argument('--include-internal', action = 'store_true',                         help = "Include internal and implicit variables")     parser.add_argument('--list', dest = 'as_text', action = 'store_true',                         help = "Output as text to the standard output stream")     parser.add_argument('--no-view', dest = 'view', action = 'store_false',                         help = "Don't open the assembled graph")      args = vars(parser.parse_args())     database = args['database'] if args['database'] else sys.stdin     make_graph(database,args['graph_name'], args['as_text'],                args['include_internal'], args['view'])      if database != sys.stdin:         database.close()