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# -*- coding: utf-8 -*-
#
# Copyright (C) 2012-2017 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 508.
"""
# Note: In PEP 345, the micro-language was Python compatible, so the ast
# module could be used to parse it. However, PEP 508 introduced operators such
# as ~= and === which aren't in Python, necessitating a different approach.
import os
import sys
import platform
from .compat import string_types
from .util import in_venv, parse_marker
__all__ = ['interpret']
def _is_literal(o):
if not isinstance(o, string_types) or not o:
return False
return o[0] in '\'"'
class Evaluator(object):
"""
This class is used to evaluate marker expessions.
"""
operations = {
'==': lambda x, y: x == y,
'===': lambda x, y: x == y,
'~=': lambda x, y: x == y or x > y,
'!=': lambda x, y: x != y,
'<': lambda x, y: x < y,
'<=': lambda x, y: x == y or x < y,
'>': lambda x, y: x > y,
'>=': lambda x, y: x == y or x > y,
'and': lambda x, y: x and y,
'or': lambda x, y: x or y,
'in': lambda x, y: x in y,
'not in': lambda x, y: x not in y,
}
def evaluate(self, expr, context):
"""
Evaluate a marker expression returned by the :func:`parse_requirement`
function in the specified context.
"""
if isinstance(expr, string_types):
if expr[0] in '\'"':
result = expr[1:-1]
else:
if expr not in context:
raise SyntaxError('unknown variable: %s' % expr)
result = context[expr]
else:
assert isinstance(expr, dict)
op = expr['op']
if op not in self.operations:
raise NotImplementedError('op not implemented: %s' % op)
elhs = expr['lhs']
erhs = expr['rhs']
if _is_literal(expr['lhs']) and _is_literal(expr['rhs']):
raise SyntaxError('invalid comparison: %s %s %s' % (elhs, op, erhs))
lhs = self.evaluate(elhs, context)
rhs = self.evaluate(erhs, context)
result = self.operations[op](lhs, rhs)
return result
def default_context():
def format_full_version(info):
version = '%s.%s.%s' % (info.major, info.minor, info.micro)
kind = info.releaselevel
if kind != 'final':
version += kind[0] + str(info.serial)
return version
if hasattr(sys, 'implementation'):
implementation_version = format_full_version(sys.implementation.version)
implementation_name = sys.implementation.name
else:
implementation_version = '0'
implementation_name = ''
result = {
'implementation_name': implementation_name,
'implementation_version': implementation_version,
'os_name': os.name,
'platform_machine': platform.machine(),
'platform_python_implementation': platform.python_implementation(),
'platform_release': platform.release(),
'platform_system': platform.system(),
'platform_version': platform.version(),
'platform_in_venv': str(in_venv()),
'python_full_version': platform.python_version(),
'python_version': platform.python_version()[:3],
'sys_platform': sys.platform,
}
return result
DEFAULT_CONTEXT = default_context()
del default_context
evaluator = Evaluator()
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
"""
try:
expr, rest = parse_marker(marker)
except Exception as e:
raise SyntaxError('Unable to interpret marker syntax: %s: %s' % (marker, e))
if rest and rest[0] != '#':
raise SyntaxError('unexpected trailing data in marker: %s: %s' % (marker, rest))
context = dict(DEFAULT_CONTEXT)
if execution_context:
context.update(execution_context)
return evaluator.evaluate(expr, context)
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