Description
Pandas version checks
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I have confirmed this issue exists on the latest version of pandas.
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I have confirmed this issue exists on the main branch of pandas.
Reproducible Example
Description
Currently, the columns variable is a list of hashable elements returned by _filter_usecols. In the dictionary comprehension at pandas/pandas/io/parsers/c_parser_wrapper.py#L262:
col_dict = {k: v for k, v in col_dict.items() if k in columns}Proposed Improvement
Convert columns to a set before performing the membership check, reducing lookup time to O(1):
columns_set = set(columns) # Convert once
col_dict = {k: v for k, v in col_dict.items() if k in columns_set}This avoids repeated list traversal and improves performance when filtering columns.
Expected Benefits
- Faster execution when columns contains many elements.
- Improved efficiency in scenarios with frequent membership checks.
Installed Versions
INSTALLED VERSIONS
commit : 0691c5c
python : 3.10.8
python-bits : 64
OS : Linux
OS-release : 6.5.0-1025-azure
Version : #26~22.04.1-Ubuntu SMP Thu Jul 11 22:33:04 UTC 2024
machine : x86_64
processor :
byteorder : little
LC_ALL : None
LANG : C.UTF-8
LOCALE : en_US.UTF-8
pandas : 2.2.3
numpy : 1.26.4
pytz : 2025.1
dateutil : 2.9.0.post0
pip : 25.0.1
Cython : 3.0.12
sphinx : 8.1.3
IPython : 8.33.0
adbc-driver-postgresql: None
adbc-driver-sqlite : None
bs4 : 4.13.3
blosc : None
bottleneck : 1.4.2
dataframe-api-compat : None
fastparquet : 2024.11.0
fsspec : 2025.2.0
html5lib : 1.1
hypothesis : 6.127.5
gcsfs : 2025.2.0
jinja2 : 3.1.5
lxml.etree : 5.3.1
matplotlib : 3.10.1
numba : 0.61.0
numexpr : 2.10.2
odfpy : None
openpyxl : 3.1.5
pandas_gbq : None
psycopg2 : 2.9.10
pymysql : 1.4.6
pyarrow : 19.0.1
pyreadstat : 1.2.8
pytest : 8.3.5
python-calamine : None
pyxlsb : 1.0.10
s3fs : 2025.2.0
scipy : 1.15.2
sqlalchemy : 2.0.38
tables : 3.10.1
tabulate : 0.9.0
xarray : 2024.9.0
xlrd : 2.0.1
xlsxwriter : 3.2.2
zstandard : 0.23.0
tzdata : 2025.1
qtpy : None
pyqt5 : None
Prior Performance
No response