docs: def compute_from_text(self,text,beta=0.001):
          """
          m.compute_from_text(,text,beta=0.001)  -- Compute a matrix values from a text string of ambiguity codes.
                                                    Use Motif_from_text utility instead to build motifs on the fly.
          """
          prevlett = {'B':'A', 'D':'C', 'V':'T', 'H':'G'}
          countmat = []
          text = re.sub('[\.\-]','N',text.upper())
          for i in range(len(text)):
              D = {'A': 0, 'C': 0, 'T':0, 'G':0}
              letter = text[i]
              if letter in ['B', 'D', 'V', 'H']:  #B == no "A", etc...
                  _omit = prevlett[letter]
                  for L in ACGT:
                      if L != _omit: D[L] = 0.3333
              elif one2two.has_key(letter):  #Covers WSMYRK
                  for L in list(one2two[letter]):
                      D[L] = 0.5
              elif letter == 'N':
                  for L in D.keys():
                      D[L] = self.background[L]
              elif letter == '@':
                  for L in D.keys():
                      D[L] = self.background[L]-(0.0001)
                  D['A'] = D['A'] + 0.0004
              else:
                  D[letter] = 1.0
              countmat.append(D)
          self.compute_from_counts(countmat,beta)