BUG: inconsistent behavior in the DataFrame.agg() when use custom aggregate function

[arlequinfei]

Pandas version checks

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of pandas.

• I have confirmed this bug exists on the main branch of pandas.

Reproducible Example

import pandas as pd

data = {
    "Product": ["apple", "pear", "banana"],
    "Sales": [100, 150, 200],
    "Price": [1, 1.5, 2],
}
df = pd.DataFrame(data)

def func1(x):
    # x is Series
    y = x.sum()
    return y

def func2(x):
    # x is a single value
    y = 0
    return y


agg_funcs = {
    "Sales": func1,
    "Price": func2
}

df_column_spec_agg = df.agg(agg_funcs)
print(df_column_spec_agg)

Issue Description

in func1() x is Series, but in func2() x is a single value.

and with an error:

ValueError: cannot perform both aggregation and transformation operations simultaneously

Expected Behavior

type(x) should be same in func1() and func2()

Installed Versions

openSUSE Leap 15.6

Python 3.12.8 (main, Dec 11 2024, 08:52:29) [GCC 13.3.0] on linux

INSTALLED VERSIONS

commit : 0691c5c
python : 3.12.8
python-bits : 64
OS : Linux
OS-release : 6.4.0-150600.23.30-default
Version : #1 SMP PREEMPT_DYNAMIC Sat Dec 7 08:37:53 UTC 2024 (8c25a0a)
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : None
LANG : en_US.UTF-8
LOCALE : en_US.UTF-8

pandas : 2.2.3
numpy : 2.2.0
pytz : 2024.2
dateutil : 2.9.0.post0
pip : 24.3.1
Cython : None
sphinx : None
IPython : 8.30.0
adbc-driver-postgresql: None
adbc-driver-sqlite : None
bs4 : 4.12.3
blosc : None
bottleneck : None
dataframe-api-compat : None
fastparquet : None
fsspec : None
html5lib : None
hypothesis : None
gcsfs : None
jinja2 : 3.1.4
lxml.etree : None
matplotlib : 3.9.3
numba : None
numexpr : None
odfpy : None
openpyxl : None
pandas_gbq : None
psycopg2 : None
pymysql : None
pyarrow : None
pyreadstat : None
pytest : None
python-calamine : None
pyxlsb : None
s3fs : None
scipy : 1.14.1
sqlalchemy : None
tables : None
tabulate : None
xarray : None
xlrd : None
xlsxwriter : None
zstandard : None
tzdata : 2024.2
qtpy : None
pyqt5 : None

[rhshadrach]

Thanks for the report! Confirmed on 2.2.x, but this is fixed on main. The OP gives the output:

Sales    450
Price      0
dtype: int64

Closing.