Apply @needs_local_scope to cell magics.

IPython/core/interactiveshell.py

@@ -2328,8 +2328,13 @@ def run_cell_magic(self, magic_name, line, cell):
                 magic_arg_s = line
             else:
                 magic_arg_s = self.var_expand(line, stack_depth)
+            kwargs = {}
+            if getattr(fn, "needs_local_scope", False):
+                kwargs['local_ns'] = sys._getframe(stack_depth).f_locals
+
             with self.builtin_trap:
-                result = fn(magic_arg_s, cell)
+                args = (magic_arg_s, cell)
+                result = fn(*args, **kwargs)
             return result
 
     def find_line_magic(self, magic_name):

docs/source/config/custommagics.rst

@@ -134,6 +134,18 @@ instantiate the class yourself before registration:
    :func:`define_magic` function are advised to adjust their code
    for the current API.
 
+
+Accessing user namespace and local scope
+========================================
+
+When creating line magics, you may need to access surrounding scope  to get user
+variables (e.g when called inside functions). IPython provide the
+``@needs_local_scope`` decorator that can be imported from
+``IPython.core.magics``. When decorated with ``@needs_local_scope`` a magic will
+be passed ``local_ns`` as an argument. As a convenience ``@needs_local_scope``
+can also be applied to cell magics even if cell magics cannot appear at local
+scope context.
+
 Complete Example
 ================