『讀碼』通常是『寫碼』的開始,尤其面對不熟悉之物件時。所以建議讀者仔細研究一下 ast.py 原始碼。比方說,追跡 dump
def dump(node, annotate_fields=True, include_attributes=False): """ Return a formatted dump of the tree in *node*. This is mainly useful for debugging purposes. The returned string will show the names and the values for fields. This makes the code impossible to evaluate, so if evaluation is wanted *annotate_fields* must be set to False. Attributes such as line numbers and column offsets are not dumped by default. If this is wanted, *include_attributes* can be set to True. """ def _format(node): if isinstance(node, AST): fields = [(a, _format(b)) for a, b in iter_fields(node)] rv = '%s(%s' % (node.__class__.__name__, ', '.join( ('%s=%s' % field for field in fields) if annotate_fields else (b for a, b in fields) )) if include_attributes and node._attributes: rv += fields and ', ' or ' ' rv += ', '.join('%s=%s' % (a, _format(getattr(node, a))) for a in node._attributes) return rv + ')' elif isinstance(node, list): return '[%s]' % ', '.join(_format(x) for x in node) return repr(node) if not isinstance(node, AST): raise TypeError('expected AST, got %r' % node.__class__.__name__) return _format(node)
def iter_fields(node): """ Yield a tuple of ``(fieldname, value)`` for each field in ``node._fields`` that is present on *node*. """ for field in node._fields: try: yield field, getattr(node, field) except AttributeError: pass
了解如何解構節點 node 也。
就會知道怎樣藉著 generic_visit ,自製小程式哩☆
如果能進一步善用他山之石
/astmonkey
Set of tools to play with Python AST.
不覺中習慣成自然◎
不必猴子天生會爬樹呦☺