ENH: Set na_filter=False as default.

Feature Type

• [ ] Adding new functionality to pandas

• [X] Changing existing functionality in pandas

• [ ] Removing existing functionality in pandas

Problem Description

When reading files, pandas reads "NA", "N/A" and other similar values as nan by default. It should not. "NA" and "N/A" could be mean two different things: "Not Available" and "Not Applicable", for instance. Or it could just be the initials for "Nadine Auburg". The default of reading these values as nan is misleading.

import pandas as pd

# test.csv file has four lines:
# a
# "NA"
# "NAN"
# "N/A"

file = 'test.csv'

df = pd.read_csv(file)

# expected df to be:
# 	a
# 0	NA
# 1	NAN
# 2	N/A

# actual:
# 	a
# 0	nan
# 1	NAN
# 2	nan

test.csv

Feature Description

Set na_filter=False as default rather than na_filter=True in pandas.read_csv (and other file-reading methods, if applicable).

Alternative Solutions

Currently the solution is to explicitly set na_filter=False when reading file. Example:

import pandas as pd

file = 'test.csv'

df = pd.read_csv(file, na_filter=False)

Additional Context

import pandas as pd

pd.show_versions()

# INSTALLED VERSIONS
# ------------------
# commit           : 8dab54d6573f7186ff0c3b6364d5e4dd635ff3e7
# python           : 3.9.15.final.0
# python-bits      : 64
# OS               : Darwin
# OS-release       : 22.1.0
# Version          : Darwin Kernel Version 22.1.0: Sun Oct  9 20:14:30 PDT 2022; root:xnu-8792.41.9~2/RELEASE_ARM64_T8103
# machine          : x86_64
# processor        : i386
# byteorder        : little
# LC_ALL           : en_CA.UTF-8
# LANG             : en_CA.UTF-8
# LOCALE           : en_CA.UTF-8

# pandas           : 1.5.2
# numpy            : 1.23.5
# pytz             : 2022.6
# dateutil         : 2.8.2
# setuptools       : 65.5.1
# pip              : 22.3.1
# Cython           : None
# pytest           : None
# hypothesis       : None
# sphinx           : 5.3.0
# blosc            : None
# feather          : None
# xlsxwriter       : None
# lxml.etree       : None
# html5lib         : None
# pymysql          : None
# psycopg2         : None
# jinja2           : 3.1.2
# IPython          : 7.33.0
# pandas_datareader: None
# bs4              : 4.11.1
# bottleneck       : None
# brotli           : 
# fastparquet      : None
# fsspec           : None
# gcsfs            : None
# matplotlib       : 3.6.2
# numba            : None
# numexpr          : None
# odfpy            : None
# openpyxl         : None
# pandas_gbq       : None
# pyarrow          : None
# pyreadstat       : None
# pyxlsb           : None
# s3fs             : None
# scipy            : 1.9.3
# snappy           : None
# sqlalchemy       : None
# tables           : None
# tabulate         : None
# xarray           : None
# xlrd             : None
# xlwt             : None
# zstandard        : None
# tzdata           : None