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      1 """Parser for future statements
      2 
      3 """
      4 
      5 from compiler import ast, walk
      6 
      7 def is_future(stmt):
      8     """Return true if statement is a well-formed future statement"""
      9     if not isinstance(stmt, ast.From):
     10         return 0
     11     if stmt.modname == "__future__":
     12         return 1
     13     else:
     14         return 0
     15 
     16 class FutureParser:
     17 
     18     features = ("nested_scopes", "generators", "division",
     19                 "absolute_import", "with_statement", "print_function",
     20                 "unicode_literals")
     21 
     22     def __init__(self):
     23         self.found = {} # set

     24 
     25     def visitModule(self, node):
     26         stmt = node.node
     27         for s in stmt.nodes:
     28             if not self.check_stmt(s):
     29                 break
     30 
     31     def check_stmt(self, stmt):
     32         if is_future(stmt):
     33             for name, asname in stmt.names:
     34                 if name in self.features:
     35                     self.found[name] = 1
     36                 else:
     37                     raise SyntaxError, \
     38                           "future feature %s is not defined" % name
     39             stmt.valid_future = 1
     40             return 1
     41         return 0
     42 
     43     def get_features(self):
     44         """Return list of features enabled by future statements"""
     45         return self.found.keys()
     46 
     47 class BadFutureParser:
     48     """Check for invalid future statements"""
     49 
     50     def visitFrom(self, node):
     51         if hasattr(node, 'valid_future'):
     52             return
     53         if node.modname != "__future__":
     54             return
     55         raise SyntaxError, "invalid future statement " + repr(node)
     56 
     57 def find_futures(node):
     58     p1 = FutureParser()
     59     p2 = BadFutureParser()
     60     walk(node, p1)
     61     walk(node, p2)
     62     return p1.get_features()
     63 
     64 if __name__ == "__main__":
     65     import sys
     66     from compiler import parseFile, walk
     67 
     68     for file in sys.argv[1:]:
     69         print file
     70         tree = parseFile(file)
     71         v = FutureParser()
     72         walk(tree, v)
     73         print v.found
     74         print
     75