Fix exceptions in whos magic command (#14970)

Correction for handling for Pandas and Polars DataFrame and Series types
for the %whos magic command. This small change reverts the most recent
changes to **namespace.py**, and relative to IPython version 8.26.0
(from my Python 3.12 install), simply adds a two-line **elif** clause to
specifically handle the case of **DataFrame** and **Series** types, as
found in Pandas and Polars. The existing code looks too generally for
variables with 'shape' and '\_\_len\_\_' attributes, which
unintentionally catches some modules and other items, and causes
exceptions. It also unintentionally hijacks correct 'default' handling
of strings and other types.

The change here is focused directly and only on the **DataFrame** and
**Series** types, and if found, shows their shape attribute. Processing
of all other types is left unchanged from 8.26.0.

Please see discussion at Issue #14952.

Note, this is my first real GitHub pull request, so please let me know
if I've done anything incorrectly, or left out any steps, as I would
like to learn from this experience!

Author: krassowski

IPython/core/magics/namespace.py

@@ -361,8 +361,7 @@ def whos(self, parameter_s=''):
           - For numpy arrays, a summary with shape, number of
             elements, typecode and size in memory.
 
-          - For objects that have shape attribute, primarily dataframe and series like
-            objects, will print the shape.
+          - For DataFrame and Series types: their shape.
 
           - Everything else: a string representation, snipping their middle if
             too long.
@@ -450,7 +449,9 @@ def type_name(v):
         Mb = 1048576  # kb**2
         for vname,var,vtype in zip(varnames,varlist,typelist):
             print(vformat.format(vname, vtype, varwidth=varwidth, typewidth=typewidth), end=' ')
-            if vtype == ndarray_type:
+            if vtype in seq_types:
+                print("n="+str(len(var)))
+            elif vtype == ndarray_type:
                 vshape = str(var.shape).replace(',','').replace(' ','x')[1:-1]
                 if vtype==ndarray_type:
                     # numpy
@@ -463,16 +464,13 @@ def type_name(v):
                 else:
                     print(aformat % (vshape, vsize, vdtype, vbytes), end=' ')
                     if vbytes < Mb:
-                        print('(%s kb)' % (vbytes/kb,))
+                        print("(%s kb)" % (vbytes / kb,))
                     else:
                         print("(%s Mb)" % (vbytes / Mb,))
-            elif hasattr(var, "shape"):
+            elif vtype in ["DataFrame", "Series"]:
                 # Useful for DataFrames and Series
                 # Ought to work for both pandas and polars
                 print(f"Shape: {var.shape}")
-            elif hasattr(var, "__len__") and not isinstance(var, str):
-                ## types that can be used in len function
-                print(f"n={len(var)}")
             else:
                 try:
                     vstr = str(var)

tests/test_magic.py

@@ -1,6 +1,7 @@
 # -*- coding: utf-8 -*-
 """Tests for various magic functions."""
 
+import collections
 import gc
 import io
 import json
@@ -768,6 +769,49 @@ def test_whos_longstr(input, expected):
     assert expected == from_whos
 
 
+def test_whos_len_namedtuple():
+    _ip = get_ipython()
+    _ip.run_line_magic("reset", "-f")
+    _ip.user_ns["alpha"] = 123
+    _ip.user_ns["beta"] = "test"
+    _ip.user_ns["nt"] = collections.namedtuple("MyNamedTuple", "col1 col2")
+    _ip.user_ns["x"] = _ip.user_ns["nt"]("a", "b")
+    expected = (
+        "Variable   Type            Data/Info\n"
+        "------------------------------------\n"
+        "alpha      int             123\n"
+        "beta       str             test\n"
+        "nt         type            <class 'tests.test_magic.MyNamedTuple'>\n"
+        "x          MyNamedTuple    MyNamedTuple(col1='a', col2='b')\n"
+    )
+    with capture_output() as captured:
+        ip.run_line_magic("whos", "")
+    stdout = captured.stdout
+    assert stdout == expected.strip() + "\n"
+
+
+@dec.skip_without("pandas")
+def test_whos_len_pandas():
+    import pandas as pd
+
+    _ip = get_ipython()
+    _ip.run_line_magic("reset", "-f")
+    df = pd.DataFrame({"a": range(10), "b": range(10, 20)})
+    _ip.user_ns["df"] = df
+    s = df["a"]
+    _ip.user_ns["s"] = s
+    expected = (
+        "Variable   Type         Data/Info\n"
+        "---------------------------------\n"
+        "df         DataFrame    Shape: (10, 2)\n"
+        "s          Series       Shape: (10,)\n"
+    )
+    with capture_output() as captured:
+        ip.run_line_magic("whos", "")
+    stdout = captured.stdout
+    assert stdout == expected.strip() + "\n"
+
+
 def doctest_precision():
     """doctest for %precision