Code Sample, a copy-pastable example if possible

In pandas 0.24 we encounter a bug where the dictionary key is not set correctly if the column name is class and we use to_dict(orient="records"). All other orientations are ok. If we use the column name klass then the records orientation is also ok. Our csv file is:

case, class 1, 1 2, 0 3, 1 4, 0 5, 1 6, 0 7, 1 8, 0 

Then, we load the data with:

read_csv(fname, skipinitialspace=True).to_dict(orient="records")

Problem description

All column names should be in the records, class has been replaced with _1 in the new version of pandas.

Expected Output

In pandas 0.23.4 the resulting dictionary is:

df: case class 0 1 1 1 2 0 2 3 1 3 4 0 4 5 1 5 6 0 6 7 1 7 8 0 to_dict: <class 'list'>: [{'case': 1, 'class': 1}, {'case': 2, 'class': 0}, {'case': 3, 'class': 1}, {'case': 4, 'class': 0}, {'case': 5, 'class': 1}, {'case': 6, 'class': 0}, {'case': 7, 'class': 1}, {'case': 8, 'class': 0}]

This is what we'd expect. However, in pandas 0.24 we get:

df: case class 0 1 1 1 2 0 2 3 1 3 4 0 4 5 1 5 6 0 6 7 1 7 8 0 to_dict: <class 'list'>: [{'case': 1, '_1': 1}, {'case': 2, '_1': 0}, {'case': 3, '_1': 1}, {'case': 4, '_1': 0}, {'case': 5, '_1': 1}, {'case': 6, '_1': 0}, {'case': 7, '_1': 1}, {'case': 8, '_1': 0}]

Note that the class column name is missing from the keys in the records. This occurs in python 3.6 and 3.7 (https://travis-ci.org/comic/evalutils/builds/486831323)

The column name class is preserved in the dictionary when using all orient="dict", "list", "series", "split" or "index".

If we change the column name to klass, then we do not get this problem using any orientation.

It is not clear to me if this solves the problem: #24965

Output of pd.show_versions()

INSTALLED VERSIONS ------------------ commit: None python: 3.6.5.final.0 python-bits: 64 OS: Linux OS-release: 4.15.0-44-generic machine: x86_64 processor: x86_64 byteorder: little LC_ALL: None LANG: en_GB.UTF-8 LOCALE: en_GB.UTF-8 pandas: 0.24.0 pytest: 3.8.0 pip: 18.0 setuptools: 40.2.0 Cython: None numpy: 1.15.1 scipy: 1.1.0 pyarrow: None xarray: None IPython: None sphinx: 1.8.0 patsy: None dateutil: 2.7.3 pytz: 2018.5 blosc: None bottleneck: None tables: None numexpr: None feather: None matplotlib: None openpyxl: None xlrd: None xlwt: None xlsxwriter: None lxml.etree: None bs4: None html5lib: None sqlalchemy: None pymysql: None psycopg2: None jinja2: 2.10 s3fs: None fastparquet: None pandas_gbq: None pandas_datareader: None gcsfs: None None