As @minrk recommends, warning if one or more symbol are not found

IPython/core/magics/code.py

@@ -31,6 +31,7 b' from IPython.utils import py3compat'
 from IPython.utils.contexts import preserve_keys
 from IPython.utils.path import get_py_filename, unquote_filename
 from IPython.utils.warn import warn
+from IPython.utils.text import get_text_list
 
 #-----------------------------------------------------------------------------
 # Magic implementation classes
@@ -48,6 +49,7 b' range_re = re.compile(r"""'
  (?P<end>\d+)?)?
 $""", re.VERBOSE)
 
+
 def extract_code_ranges(ranges_str):
     """Turn a string of range for %%load into 2-tuples of (start, stop)
     ready to use as a slice of the content splitted by lines.
@@ -80,18 +82,21 b' def extract_code_ranges(ranges_str):'
 @skip_doctest
 def extract_symbols(code, symbols):
     """
-    Return a list of code fragments for each symbol parsed from code
-    For example, suppose code is a string::
+    Return a tuple  (blocks, not_found)
+    where ``blocks`` is a list of code fragments
+    for each symbol parsed from code, and ``not_found`` are
+    symbols not found in the code.
+
+    For example::
 
-        a = 10
+        >>> code = '''a = 10
 
         def b(): return 42
 
-        class A: pass
+        class A: pass'''
 
         >>> extract_symbols(code, 'A,b')
-
-            ["class A: pass", "def b(): return 42"]
+        (["class A: pass", "def b(): return 42"], [])
     """
     try:
         py_code = ast.parse(code)
@@ -115,12 +120,15 b' def extract_symbols(code, symbols):'
 
     # fill a list with chunks of codes for each symbol
     blocks = []
+    not_found = []
     for symbol in symbols.split(','):
         if symbol in symbols_lines:
             start, end = symbols_lines[symbol]
             blocks.append('\n'.join(code[start:end]) + '\n')
+        else:
+            not_found.append(symbol)
 
-    return blocks
+    return blocks, not_found
 
 
 class InteractivelyDefined(Exception):
@@ -289,7 +297,15 b' class CodeMagics(Magics):'
         contents = self.shell.find_user_code(args)
 
         if 's' in opts:
-            contents = '\n'.join(extract_symbols(contents, opts['s']))
+            blocks, not_found = extract_symbols(contents, opts['s'])
+            if len(not_found) == 1:
+                warn('The symbol `%s` was not found' % not_found[0])
+            elif len(not_found) > 1:
+                warn('The symbols %s were not found' % get_text_list(not_found,
+                                                                     wrap_item_with='`')
+                )
+
+            contents = '\n'.join(blocks)
 
         if 'r' in opts:
             ranges = opts['r'].replace(',', ' ')

IPython/core/tests/test_magic.py

@@ -64,12 +64,12 b' def test_extract_code_ranges():'
 def test_extract_symbols():
     source = """import foo\na = 10\ndef b():\n    return 42\n\n\nclass A: pass\n\n\n"""
     symbols_args = ["a", "b", "A", "A,b", "A,a", "z"]
-    expected = [[],
-                ["def b():\n    return 42\n"],
-                ["class A: pass\n"],
-                ["class A: pass\n", "def b():\n    return 42\n"],
-                ["class A: pass\n"],
-                []]
+    expected = [([], ['a']),
+                (["def b():\n    return 42\n"], []),
+                (["class A: pass\n"], []),
+                (["class A: pass\n", "def b():\n    return 42\n"], []),
+                (["class A: pass\n"], ['a']),
+                ([], ['z'])]
     for symbols, exp in zip(symbols_args, expected):
         nt.assert_equal(code.extract_symbols(source, symbols), exp)