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EDIT :: markers.py

# -*- coding: utf-8 -*- # # Copyright (C) 2012-2013 Vinay Sajip. # Licensed to the Python Software Foundation under a contributor agreement. # See LICENSE.txt and CONTRIBUTORS.txt. # """Parser for the environment markers micro-language defined in PEP 345.""" import ast import os import sys import platform from .compat import python_implementation, string_types from .util import in_venv __all__ = ['interpret'] class Evaluator(object): """ A limited evaluator for Python expressions. """ operators = { 'eq': lambda x, y: x == y, 'gt': lambda x, y: x > y, 'gte': lambda x, y: x >= y, 'in': lambda x, y: x in y, 'lt': lambda x, y: x < y, 'lte': lambda x, y: x <= y, 'not': lambda x: not x, 'noteq': lambda x, y: x != y, 'notin': lambda x, y: x not in y, } allowed_values = { 'sys_platform': sys.platform, 'python_version': '%s.%s' % sys.version_info[:2], # parsing sys.platform is not reliable, but there is no other # way to get e.g. 2.7.2+, and the PEP is defined with sys.version 'python_full_version': sys.version.split(' ', 1)[0], 'os_name': os.name, 'platform_in_venv': str(in_venv()), 'platform_release': platform.release(), 'platform_version': platform.version(), 'platform_machine': platform.machine(), 'platform_python_implementation': python_implementation(), } def __init__(self, context=None): """ Initialise an instance. :param context: If specified, names are looked up in this mapping. """ self.context = context or {} self.source = None def get_fragment(self, offset): """ Get the part of the source which is causing a problem. """ fragment_len = 10 s = '%r' % (self.source[offset:offset + fragment_len]) if offset + fragment_len < len(self.source): s += '...' return s def get_handler(self, node_type): """ Get a handler for the specified AST node type. """ return getattr(self, 'do_%s' % node_type, None) def evaluate(self, node, filename=None): """ Evaluate a source string or node, using ``filename`` when displaying errors. """ if isinstance(node, string_types): self.source = node kwargs = {'mode': 'eval'} if filename: kwargs['filename'] = filename try: node = ast.parse(node, **kwargs) except SyntaxError as e: s = self.get_fragment(e.offset) raise SyntaxError('syntax error %s' % s) node_type = node.__class__.__name__.lower() handler = self.get_handler(node_type) if handler is None: if self.source is None: s = '(source not available)' else: s = self.get_fragment(node.col_offset) raise SyntaxError("don't know how to evaluate %r %s" % ( node_type, s)) return handler(node) def get_attr_key(self, node): assert isinstance(node, ast.Attribute), 'attribute node expected' return '%s.%s' % (node.value.id, node.attr) def do_attribute(self, node): if not isinstance(node.value, ast.Name): valid = False else: key = self.get_attr_key(node) valid = key in self.context or key in self.allowed_values if not valid: raise SyntaxError('invalid expression: %s' % key) if key in self.context: result = self.context[key] else: result = self.allowed_values[key] return result def do_boolop(self, node): result = self.evaluate(node.values[0]) is_or = node.op.__class__ is ast.Or is_and = node.op.__class__ is ast.And assert is_or or is_and if (is_and and result) or (is_or and not result): for n in node.values[1:]: result = self.evaluate(n) if (is_or and result) or (is_and and not result): break return result def do_compare(self, node): def sanity_check(lhsnode, rhsnode): valid = True if isinstance(lhsnode, ast.Str) and isinstance(rhsnode, ast.Str): valid = False #elif (isinstance(lhsnode, ast.Attribute) # and isinstance(rhsnode, ast.Attribute)): # klhs = self.get_attr_key(lhsnode) # krhs = self.get_attr_key(rhsnode) # valid = klhs != krhs if not valid: s = self.get_fragment(node.col_offset) raise SyntaxError('Invalid comparison: %s' % s) lhsnode = node.left lhs = self.evaluate(lhsnode) result = True for op, rhsnode in zip(node.ops, node.comparators): sanity_check(lhsnode, rhsnode) op = op.__class__.__name__.lower() if op not in self.operators: raise SyntaxError('unsupported operation: %r' % op) rhs = self.evaluate(rhsnode) result = self.operators[op](lhs, rhs) if not result: break lhs = rhs lhsnode = rhsnode return result def do_expression(self, node): return self.evaluate(node.body) def do_name(self, node): valid = False if node.id in self.context: valid = True result = self.context[node.id] elif node.id in self.allowed_values: valid = True result = self.allowed_values[node.id] if not valid: raise SyntaxError('invalid expression: %s' % node.id) return result def do_str(self, node): return node.s def interpret(marker, execution_context=None): """ Interpret a marker and return a result depending on environment. :param marker: The marker to interpret. :type marker: str :param execution_context: The context used for name lookup. :type execution_context: mapping """ return Evaluator(execution_context).evaluate(marker.strip())

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