pd.read_csv does not recognize scientific notation if 'decimal' attribute is set with engine=python

[onnoeberhard]

Contents of 'abc.tsv':

a	b
1,2	3,5E-1
1,2e2	3,5

Code:

>>> import pandas as pd
>>> pd.read_csv('abc.tsv', '\t', decimal=',')
       a     b
0    1.2  0.35
1  120.0  3.50
>>> pd.read_csv('abc.tsv', '\t', decimal=',', engine='python')
       a       b
0    1.2  3,5E-1
1  1,2e2     3.5

Problem description

The outputs of the two read_csv commands above should be the same. In this case an obvious "solution" is to just use the C-engine, however I have to process a file where I need to use a regular expression as the delimiter.

Expected Output

>>> pd.read_csv('abc.tsv', '\t', decimal=',', engine='python')
       a     b
0    1.2  0.35
1  120.0  3.50

Output of pd.show_versions()

INSTALLED VERSIONS

commit : None
python : 3.7.6.final.0
python-bits : 64
OS : Darwin
OS-release : 19.2.0
machine : x86_64
processor : i386
byteorder : little
LC_ALL : en_US.UTF-8
LANG : None
LOCALE : en_US.UTF-8

pandas : 1.0.1
numpy : 1.18.1
pytz : 2019.3
dateutil : 2.8.1
pip : 20.0.2
setuptools : 45.2.0.post20200210
Cython : 0.29.15
pytest : 5.3.5
hypothesis : 5.4.1
sphinx : 2.4.0
blosc : None
feather : None
xlsxwriter : 1.2.7
lxml.etree : 4.5.0
html5lib : 1.0.1
pymysql : None
psycopg2 : None
jinja2 : 2.11.1
IPython : 7.12.0
pandas_datareader: None
bs4 : 4.8.2
bottleneck : 1.3.1
fastparquet : None
gcsfs : None
lxml.etree : 4.5.0
matplotlib : 3.1.3
numexpr : 2.7.1
odfpy : None
openpyxl : 3.0.3
pandas_gbq : None
pyarrow : None
pytables : None
pytest : 5.3.5
pyxlsb : None
s3fs : None
scipy : 1.4.1
sqlalchemy : 1.3.13
tables : 3.6.1
tabulate : None
xarray : None
xlrd : 1.2.0
xlwt : 1.3.0
xlsxwriter : 1.2.7
numba : 0.48.0