code: def MergeFlags(self, args, unique=1, dict=None):
          
  
          if dict is None:
              dict = self
          if not SCons.Util.is_Dict(args):
              args = self.ParseFlags(args)
          if not unique:
              self.Append(**args)
              return self
          for key, value in args.items():
              if not value:
                  continue
              try:
                  orig = self[key]
              except KeyError:
                  orig = value
              else:
                  if not orig:
                      orig = value
                  elif value:
                      # Add orig and value.  The logic here was lifted from
                      # part of env.Append() (see there for a lot of comments
                      # about the order in which things are tried) and is
                      # used mainly to handle coercion of strings to CLVar to
                      # "do the right thing" given (e.g.) an original CCFLAGS
                      # string variable like '-pipe -Wall'.
                      try:
                          orig = orig + value
                      except (KeyError, TypeError):
                          try:
                              add_to_orig = orig.append
                          except AttributeError:
                              value.insert(0, orig)
                              orig = value
                          else:
                              add_to_orig(value)
              t = []
              if key[-4:] == 'PATH':
                  ### keep left-most occurence
                  for v in orig:
                      if v not in t:
                          t.append(v)
              else:
                  ### keep right-most occurence
                  orig.reverse()
                  for v in orig:
                      if v not in t:
                          t.insert(0, v)
              self[key] = t
          return self
docs: Merge the dict in args into the construction variables of this
          env, or the passed-in dict.  If args is not a dict, it is
          converted into a dict using ParseFlags.  If unique is not set,
          the flags are appended rather than merged.