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211 lines
7.0 KiB
Python
211 lines
7.0 KiB
Python
2 years ago
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# Copyright 2004-2005 Elemental Security, Inc. All Rights Reserved.
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# Licensed to PSF under a Contributor Agreement.
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# Modifications:
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# Copyright David Halter and Contributors
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# Modifications are dual-licensed: MIT and PSF.
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# 99% of the code is different from pgen2, now.
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"""
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The ``Parser`` tries to convert the available Python code in an easy to read
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format, something like an abstract syntax tree. The classes who represent this
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tree, are sitting in the :mod:`parso.tree` module.
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The Python module ``tokenize`` is a very important part in the ``Parser``,
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because it splits the code into different words (tokens). Sometimes it looks a
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bit messy. Sorry for that! You might ask now: "Why didn't you use the ``ast``
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module for this? Well, ``ast`` does a very good job understanding proper Python
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code, but fails to work as soon as there's a single line of broken code.
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There's one important optimization that needs to be known: Statements are not
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being parsed completely. ``Statement`` is just a representation of the tokens
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within the statement. This lowers memory usage and cpu time and reduces the
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complexity of the ``Parser`` (there's another parser sitting inside
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``Statement``, which produces ``Array`` and ``Call``).
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"""
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from typing import Dict, Type
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from parso import tree
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from parso.pgen2.generator import ReservedString
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class ParserSyntaxError(Exception):
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"""
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Contains error information about the parser tree.
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May be raised as an exception.
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"""
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def __init__(self, message, error_leaf):
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self.message = message
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self.error_leaf = error_leaf
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class InternalParseError(Exception):
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"""
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Exception to signal the parser is stuck and error recovery didn't help.
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Basically this shouldn't happen. It's a sign that something is really
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wrong.
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"""
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def __init__(self, msg, type_, value, start_pos):
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Exception.__init__(self, "%s: type=%r, value=%r, start_pos=%r" %
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(msg, type_.name, value, start_pos))
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self.msg = msg
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self.type = type
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self.value = value
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self.start_pos = start_pos
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class Stack(list):
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def _allowed_transition_names_and_token_types(self):
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def iterate():
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# An API just for Jedi.
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for stack_node in reversed(self):
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for transition in stack_node.dfa.transitions:
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if isinstance(transition, ReservedString):
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yield transition.value
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else:
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yield transition # A token type
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if not stack_node.dfa.is_final:
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break
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return list(iterate())
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class StackNode:
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def __init__(self, dfa):
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self.dfa = dfa
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self.nodes = []
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@property
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def nonterminal(self):
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return self.dfa.from_rule
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def __repr__(self):
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return '%s(%s, %s)' % (self.__class__.__name__, self.dfa, self.nodes)
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def _token_to_transition(grammar, type_, value):
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# Map from token to label
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if type_.value.contains_syntax:
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# Check for reserved words (keywords)
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try:
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return grammar.reserved_syntax_strings[value]
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except KeyError:
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pass
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return type_
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class BaseParser:
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"""Parser engine.
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A Parser instance contains state pertaining to the current token
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sequence, and should not be used concurrently by different threads
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to parse separate token sequences.
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See python/tokenize.py for how to get input tokens by a string.
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When a syntax error occurs, error_recovery() is called.
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"""
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node_map: Dict[str, Type[tree.BaseNode]] = {}
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default_node = tree.Node
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leaf_map: Dict[str, Type[tree.Leaf]] = {}
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default_leaf = tree.Leaf
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def __init__(self, pgen_grammar, start_nonterminal='file_input', error_recovery=False):
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self._pgen_grammar = pgen_grammar
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self._start_nonterminal = start_nonterminal
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self._error_recovery = error_recovery
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def parse(self, tokens):
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first_dfa = self._pgen_grammar.nonterminal_to_dfas[self._start_nonterminal][0]
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self.stack = Stack([StackNode(first_dfa)])
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for token in tokens:
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self._add_token(token)
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while True:
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tos = self.stack[-1]
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if not tos.dfa.is_final:
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# We never broke out -- EOF is too soon -- Unfinished statement.
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# However, the error recovery might have added the token again, if
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# the stack is empty, we're fine.
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raise InternalParseError(
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"incomplete input", token.type, token.string, token.start_pos
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)
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if len(self.stack) > 1:
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self._pop()
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else:
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return self.convert_node(tos.nonterminal, tos.nodes)
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def error_recovery(self, token):
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if self._error_recovery:
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raise NotImplementedError("Error Recovery is not implemented")
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else:
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type_, value, start_pos, prefix = token
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error_leaf = tree.ErrorLeaf(type_, value, start_pos, prefix)
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raise ParserSyntaxError('SyntaxError: invalid syntax', error_leaf)
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def convert_node(self, nonterminal, children):
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try:
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node = self.node_map[nonterminal](children)
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except KeyError:
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node = self.default_node(nonterminal, children)
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return node
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def convert_leaf(self, type_, value, prefix, start_pos):
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try:
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return self.leaf_map[type_](value, start_pos, prefix)
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except KeyError:
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return self.default_leaf(value, start_pos, prefix)
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def _add_token(self, token):
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"""
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This is the only core function for parsing. Here happens basically
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everything. Everything is well prepared by the parser generator and we
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only apply the necessary steps here.
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"""
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grammar = self._pgen_grammar
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stack = self.stack
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type_, value, start_pos, prefix = token
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transition = _token_to_transition(grammar, type_, value)
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while True:
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try:
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plan = stack[-1].dfa.transitions[transition]
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break
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except KeyError:
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if stack[-1].dfa.is_final:
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self._pop()
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else:
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self.error_recovery(token)
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return
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except IndexError:
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raise InternalParseError("too much input", type_, value, start_pos)
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stack[-1].dfa = plan.next_dfa
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for push in plan.dfa_pushes:
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stack.append(StackNode(push))
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leaf = self.convert_leaf(type_, value, prefix, start_pos)
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stack[-1].nodes.append(leaf)
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def _pop(self):
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tos = self.stack.pop()
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# If there's exactly one child, return that child instead of
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# creating a new node. We still create expr_stmt and
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# file_input though, because a lot of Jedi depends on its
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# logic.
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if len(tos.nodes) == 1:
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new_node = tos.nodes[0]
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else:
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new_node = self.convert_node(tos.dfa.from_rule, tos.nodes)
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self.stack[-1].nodes.append(new_node)
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