add markerlib as _markerlib

--HG--
branch : distribute
extra : rebase_source : b9d8fa81db6c6fc3d89db54a70778eb3e8396e17

1 files changed, 110 insertions, 0 deletions

diff --git a/_markerlib/markers.py b/_markerlib/markers.py
new file mode 100644
index 00000000..293adf72
--- /dev/null
+++ b/_markerlib/markers.py
@@ -0,0 +1,110 @@
+# -*- 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]
+    os.name = os.name
+    sys.platform = sys.platform
+    platform.version = platform.version()
+    platform.machine = platform.machine()
+    platform.python_implementation = platform.python_implementation()
+    a free string, like '2.4', or 'win32'
+"""
+
+__all__ = ['default_environment', 'compile', 'interpret']
+
+# Would import from ast but for Python 2.5
+from _ast import Compare, BoolOp, Attribute, Name, Load, Str, cmpop, boolop
+try:
+    from ast import parse, copy_location, NodeTransformer
+except ImportError: # pragma no coverage
+    from markerlib._markers_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],
+         'os.name': os.name,
+         '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' %
+                               (self.statement, 
+                               (' ' * 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.value.id, 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',
+                   dont_inherit=True)
+
+_cache = weakref.WeakValueDictionary()
+
+def compile(marker):
+    """Return compiled marker as a function accepting an environment dict."""
+    try:
+        return _cache[marker]
+    except KeyError:
+        pass
+    if not marker.strip():
+        def marker_fn(environment=None, override=None):
+            """"""
+            return True
+    else:
+        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()
+            environment.update(override)
+            return eval(compiled_marker, environment)
+    marker_fn.__doc__ = marker
+    _cache[marker] = marker_fn
+    return _cache[marker]
+
+as_function = compile # bw compat
+
+def interpret(marker, environment=None):
+    return compile(marker)(environment)