python - PLY - 返回多个 token

Question

据我所知，对 Python 源代码进行词法分析的技术是:

• 当当前行的缩进级别小于上一行的缩进级别时，产生 DEDENT。如果要关闭多个 INDENT，则生成多个 DEDENT。
• 当到达输入末尾时，如果有未关闭的 INDENT(s)，则产生 DEDENT(s)。

现在，使用 PLY:

• 如何从 t_definition 返回多个标记？
• 如何创建一个在到达 EOF 时调用的 t_definition？简单的 \Z 不起作用——PLY 提示它匹配空字符串。

Answer 1

据我所知，PLY 没有实现推送解析器接口(interface)，而这是使用 bison 最容易解决这个问题的方法。但是，很容易注入(inject)您自己的词法分析器包装器，它可以处理 dedent 标记队列。

最小的词法分析器实现需要实现一个 token() 方法，该方法返回一个具有 type 和 value 属性的对象。 (如果您的解析器使用它，您也需要它，但我不会在这里担心。)

现在，让我们假设底层(PLY 生成的)词法分析器生成 NEWLINE 标记，其值是换行符后前导空格的长度。如果某些行不参与 INDENT/DEDENT 算法，则应为这些行抑制 NEWLINE；我们这里不考虑这种情况。一个简单的示例词法分析器函数(仅适用于空格，不适用于制表符)可能是:

# This function doesn't handle tabs. Beware!
def t_NEWLINE(self, t):
  r'\n(?:\s*(?:[#].*)?\n)*\s*'
  t.value = len(t.value) - 1 - t.value.rfind('\n')
  return t

现在我们用处理缩进的包装器包装 PLY 生成的词法分析器:

# WARNING:
# This code hasn't been tested much and it also may be inefficient
# and/or inexact. It doesn't do python-style tab handling. Etc. etc.

from collections import namedtuple, deque

# These are the tokens. We only generate one of each here. If
# we used lineno or didn't trust the parser to not mess with the
# token, we could generate a new one each time.
IndentToken = namedtuple('Token', 'type value')
dedent = IndentToken('DEDENT', None)
indent = IndentToken('INDENT', None)
newline= IndentToken('NEWLINE', None)

class IndentWrapper(object):

  def __init__(self, lexer):
    """Create a new wrapper given the lexer which is being wrapped"""
    self.lexer = lexer
    self.indent_stack = [0]
    # A queue is overkill for this case, but it's simple.
    self.token_queue = deque()
    # This is just in case the ply-generated lexer cannot be called again
    # after it returns None.
    self.eof_reached = False

  def token(self):
    """Return the next token, or None if end of input has been reached"""
    # Do we have any queued tokens?
    if self.token_queue:
      return self.token_queue.popleft()
    # Are we done?
    if self.eof_reached:
      return None
    # Get a token
    t = self.lexer.token()
    if t is None:
      # At end of input, we might need to send some dedents
      self.eof_reached = True
      if len(self.indent_stack) > 1:
        t = dedent
        for i in range(len(self.indent_stack) - 1):
          self.token_queue.append(dedent)
        self.indent_stack = [0]
    elif t.type == "NEWLINE":
      # The NEWLINE token includes the amount of leading whitespace.
      # Fabricate indent or dedents as/if necessary and queue them.
      if t.value > self.indent_stack[-1]:
        self.indent_stack.append(t.value)
        self.token_queue.append(indent)
      else:
        while t.value < self.indent_stack[-1]:
          self.indent_stack.pop()
          self.token_queue.append(dedent)
        if t.value != self.indent_stack[-1]:
          raise IndentError # Or however you indicate errors
    return t