def clipByAnnotation(self, key, chars=""):
        if key not in self.mAnnotations:
            return
        if chars == "":
            return
        if self.getNumColumns() == 0:
            return

        anno = self.mAnnotations[key]
        columns = []

        for x in range(len(anno)):
            if anno[x] in chars:
                columns.append(x)

        self.takeColumns(columns)
restrict alignment to positions where annotation identified by key
dataset/ETHPy150Open CGATOxford/cgat/CGAT/Mali.py/Mali.clipByAnnotation