code: def from_clauses(self, clauses):
          
  
          self.clauses = copy.deepcopy(clauses)
  
          for cl in self.clauses:
              self.nv = max([abs(l) for l in cl] + [self.nv])
docs: This methods copies a list of clauses into a CNF object.
  
              :param clauses: a list of clauses.
              :type clauses: list(list(int))
  
              Example:
  
              .. code-block:: python
  
                  >>> from pysat.formula import CNF
                  >>> cnf = CNF(from_clauses=[[-1, 2], [1, -2], [5]])
                  >>> print cnf.clauses
                  [[-1, 2], [1, -2], [5]]
                  >>> print cnf.nv
                  5