def _delete_instructions(self, instruction, value=None):
if instruction == '<STR_LIT>' and value:<EOL><INDENT>self._modify_instruction_label(value, None)<EOL>return<EOL><DEDENT>if instruction == '<STR_LIT>' and value:<EOL><INDENT>self._modify_instruction_env(value, None)<EOL>return<EOL><DEDENT>lines = self.lines<EOL>deleted = False<EOL>for insn in reversed(self.structure):<EOL><INDENT>if insn['<STR_LIT>'] == instruction:<EOL><INDENT>if value and insn['<STR_LIT:value>'] != value:<EOL><INDENT>continue<EOL><DEDENT>deleted = True<EOL>del lines[insn['<STR_LIT>']:insn['<STR_LIT>'] + <NUM_LIT:1>]<EOL><DEDENT><DEDENT>if deleted:<EOL><INDENT>self.lines = lines<EOL><DEDENT>
:param instruction: name of instruction to be deleted
:param value: if specified, delete instruction only when it has this value
              if instruction is LABEL then value is label name