distribute / _markerlib /

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# -*- coding: utf-8 -*-
"""Interpret PEP 345 environment markers.

EXPR [in|==|!=|not in] EXPR [or|and] ...

where EXPR belongs to any of those:

    python_version = '%s.%s' % (sys.version_info[0], sys.version_info[1])
    python_full_version = sys.version.split()[0] =
    sys.platform = sys.platform
    platform.version = platform.version()
    platform.machine = platform.machine()
    platform.python_implementation = platform.python_implementation()
    a free string, like '2.6', or 'win32'

__all__ = ['default_environment', 'compile', 'interpret']

from ast import Compare, BoolOp, Attribute, Name, Load, Str, cmpop, boolop
from ast import parse, copy_location, NodeTransformer

import os
import platform
import sys
import weakref

_builtin_compile = compile

from platform import python_implementation

# restricted set of variables
_VARS = {'sys.platform': sys.platform,
         'python_version': '%s.%s' % sys.version_info[:2],
         # FIXME 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],
         'platform.version': platform.version(),
         'platform.machine': platform.machine(),
         'platform.python_implementation': python_implementation(),
         'extra': None # wheel extension

def default_environment():
    """Return copy of default PEP 385 globals dictionary."""
    return dict(_VARS)

class ASTWhitelist(NodeTransformer):
    def __init__(self, statement):
        self.statement = statement # for error messages
    ALLOWED = (Compare, BoolOp, Attribute, Name, Load, Str, cmpop, boolop)
    def visit(self, node):
        """Ensure statement only contains allowed nodes."""
        if not isinstance(node, self.ALLOWED):
            raise SyntaxError('Not allowed in environment markers.\n%s\n%s' %
                               (' ' * node.col_offset) + '^'))
        return NodeTransformer.visit(self, node)
    def visit_Attribute(self, node):
        """Flatten one level of attribute access."""
        new_node = Name("%s.%s" % (, node.attr), node.ctx)
        return copy_location(new_node, node)

def parse_marker(marker):
    tree = parse(marker, mode='eval')
    new_tree = ASTWhitelist(marker).generic_visit(tree)
    return new_tree

def compile_marker(parsed_marker):
    return _builtin_compile(parsed_marker, '<environment marker>', 'eval',

_cache = weakref.WeakValueDictionary()

def compile(marker):
    """Return compiled marker as a function accepting an environment dict."""
        return _cache[marker]
    except KeyError:
    if not marker.strip():
        def marker_fn(environment=None, override=None):
            return True
        compiled_marker = compile_marker(parse_marker(marker))
        def marker_fn(environment=None, override=None):
            """override updates environment"""
            if override is None:
                override = {}
            if environment is None:
                environment = default_environment()
            return eval(compiled_marker, environment)
    marker_fn.__doc__ = marker
    _cache[marker] = marker_fn
    return _cache[marker]

def interpret(marker, environment=None):
    return compile(marker)(environment)