1 files changed, 187 insertions, 0 deletions
diff --git a/Lib/packaging/markers.py b/Lib/packaging/markers.py
new file mode 100644
index 0000000000..4bbac7eca7
--- /dev/null
+++ b/Lib/packaging/markers.py
@@ -0,0 +1,187 @@
+"""Parser for the environment markers micro-language defined in PEP 345."""
+
+import sys
+import platform
+import os
+
+from tokenize import tokenize, NAME, OP, STRING, ENDMARKER, ENCODING
+from io import BytesIO
+
+__all__ = ['interpret']
+
+
+# allowed operators
+_OPERATORS = {'==': lambda x, y: x == y,
+              '!=': lambda x, y: x != y,
+              '>': lambda x, y: x > y,
+              '>=': lambda x, y: x >= y,
+              '<': lambda x, y: x < y,
+              '<=': lambda x, y: x <= y,
+              'in': lambda x, y: x in y,
+              'not in': lambda x, y: x not in y}
+
+
+def _operate(operation, x, y):
+    return _OPERATORS[operation](x, y)
+
+
+# restricted set of variables
+_VARS = {'sys.platform': sys.platform,
+         'python_version': sys.version[:3],
+         'python_full_version': sys.version.split(' ', 1)[0],
+         'os.name': os.name,
+         'platform.version': platform.version(),
+         'platform.machine': platform.machine(),
+         'platform.python_implementation': platform.python_implementation()}
+
+
+class _Operation:
+
+    def __init__(self, execution_context=None):
+        self.left = None
+        self.op = None
+        self.right = None
+        if execution_context is None:
+            execution_context = {}
+        self.execution_context = execution_context
+
+    def _get_var(self, name):
+        if name in self.execution_context:
+            return self.execution_context[name]
+        return _VARS[name]
+
+    def __repr__(self):
+        return '%s %s %s' % (self.left, self.op, self.right)
+
+    def _is_string(self, value):
+        if value is None or len(value) < 2:
+            return False
+        for delimiter in '"\'':
+            if value[0] == value[-1] == delimiter:
+                return True
+        return False
+
+    def _is_name(self, value):
+        return value in _VARS
+
+    def _convert(self, value):
+        if value in _VARS:
+            return self._get_var(value)
+        return value.strip('"\'')
+
+    def _check_name(self, value):
+        if value not in _VARS:
+            raise NameError(value)
+
+    def _nonsense_op(self):
+        msg = 'This operation is not supported : "%s"' % self
+        raise SyntaxError(msg)
+
+    def __call__(self):
+        # make sure we do something useful
+        if self._is_string(self.left):
+            if self._is_string(self.right):
+                self._nonsense_op()
+            self._check_name(self.right)
+        else:
+            if not self._is_string(self.right):
+                self._nonsense_op()
+            self._check_name(self.left)
+
+        if self.op not in _OPERATORS:
+            raise TypeError('Operator not supported "%s"' % self.op)
+
+        left = self._convert(self.left)
+        right = self._convert(self.right)
+        return _operate(self.op, left, right)
+
+
+class _OR:
+    def __init__(self, left, right=None):
+        self.left = left
+        self.right = right
+
+    def filled(self):
+        return self.right is not None
+
+    def __repr__(self):
+        return 'OR(%r, %r)' % (self.left, self.right)
+
+    def __call__(self):
+        return self.left() or self.right()
+
+
+class _AND:
+    def __init__(self, left, right=None):
+        self.left = left
+        self.right = right
+
+    def filled(self):
+        return self.right is not None
+
+    def __repr__(self):
+        return 'AND(%r, %r)' % (self.left, self.right)
+
+    def __call__(self):
+        return self.left() and self.right()
+
+
+def interpret(marker, execution_context=None):
+    """Interpret a marker and return a result depending on environment."""
+    marker = marker.strip().encode()
+    ops = []
+    op_starting = True
+    for token in tokenize(BytesIO(marker).readline):
+        # Unpack token
+        toktype, tokval, rowcol, line, logical_line = token
+        if toktype not in (NAME, OP, STRING, ENDMARKER, ENCODING):
+            raise SyntaxError('Type not supported "%s"' % tokval)
+
+        if op_starting:
+            op = _Operation(execution_context)
+            if len(ops) > 0:
+                last = ops[-1]
+                if isinstance(last, (_OR, _AND)) and not last.filled():
+                    last.right = op
+                else:
+                    ops.append(op)
+            else:
+                ops.append(op)
+            op_starting = False
+        else:
+            op = ops[-1]
+
+        if (toktype == ENDMARKER or
+            (toktype == NAME and tokval in ('and', 'or'))):
+            if toktype == NAME and tokval == 'and':
+                ops.append(_AND(ops.pop()))
+            elif toktype == NAME and tokval == 'or':
+                ops.append(_OR(ops.pop()))
+            op_starting = True
+            continue
+
+        if isinstance(op, (_OR, _AND)) and op.right is not None:
+            op = op.right
+
+        if ((toktype in (NAME, STRING) and tokval not in ('in', 'not'))
+            or (toktype == OP and tokval == '.')):
+            if op.op is None:
+                if op.left is None:
+                    op.left = tokval
+                else:
+                    op.left += tokval
+            else:
+                if op.right is None:
+                    op.right = tokval
+                else:
+                    op.right += tokval
+        elif toktype == OP or tokval in ('in', 'not'):
+            if tokval == 'in' and op.op == 'not':
+                op.op = 'not in'
+            else:
+                op.op = tokval
+
+    for op in ops:
+        if not op():
+            return False
+    return True