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# -*- 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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