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Reproducible Example

import pandas as pd  # version 1.5.2
import io

data = """a;b;c\n0000.7995;16.000;0\n3.03.001.00514;0;4.000\n4923.600.041;23.000;131"""

df1 = pd.read_csv(io.StringIO(data), sep=';', dtype={'a': str}, thousands='.', engine='c')
df2 = pd.read_csv(io.StringIO(data), sep=';', dtype={'a': str}, thousands='.', engine='python')

Issue Description

Dots are stripped from strings that consist of numbers and dots, when engine='python' ('c' works fine), even when dtype is set explicitly. The unexpected behaviour is experienced when processing a csv file that has strings that solely consist of numbers and single dots spread throughout the string the read_csv parameters are set: engine='python' and thousands='.'

The issue was initially filed on stackoverflow.

Expected Behavior

Dots are not stripped from the columns if str type is set up.

Installed Versions

INSTALLED VERSIONS

commit : 8dab54d6573f7186ff0c3b6364d5e4dd635ff3e7 python : 3.9.0.final.0 python-bits : 64 OS : Windows OS-release : 10 Version : 10.0.19041 machine : AMD64 processor : AMD64 Family 25 Model 80 Stepping 0, AuthenticAMD byteorder : little LC_ALL : None LANG : None LOCALE : Russian_Russia.1252

pandas : 1.5.2 numpy : 1.22.1 pytz : 2022.1 dateutil : 2.8.2 setuptools : 65.5.0 pip : 22.3.1 Cython : None pytest : None hypothesis : None sphinx : None blosc : None feather : None xlsxwriter : None lxml.etree : 4.6.3 html5lib : None pymysql : None psycopg2 : 2.9.3 jinja2 : 3.1.0 IPython : 7.29.0 pandas_datareader: None bs4 : 4.11.1 bottleneck : None brotli : 1.0.9 fastparquet : None fsspec : None gcsfs : None matplotlib : 3.4.3 numba : None numexpr : None odfpy : None openpyxl : 3.0.9 pandas_gbq : None pyarrow : 8.0.0 pyreadstat : None pyxlsb : None s3fs : None scipy : 1.7.3 snappy : None sqlalchemy : 1.4.44 tables : None tabulate : None xarray : None xlrd : None xlwt : None zstandard : None tzdata : 2022.4

Comment From: MarcoGorelli

Thanks for the report, can confirm this reproduces