connect using env. variables

Please, there should be a possibility to call connect() without parameters
for connecting using environment variables (PGSERVICE, PGDATABASE,…)
or defaults ($USER(at)localhost/postgres).

Even pg uri postgres:// is valid,
https://www.postgresql.org/docs/current/libpq-connect.html.

>>> d = psycopg2.connect(**parse_dsn('postgres://'))
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib/python3/dist-packages/psycopg2/__init__.py", line 124, in connect
raise TypeError('missing dsn and no parameters')
TypeError: missing dsn and no parameters
>>> d = psycopg2.connect(**parse_dsn(''))
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib/python3/dist-packages/psycopg2/__init__.py", line 124, in connect
raise TypeError('missing dsn and no parameters')
TypeError: missing dsn and no parameters
>>> db = psycopg2.connect()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib/python3/dist-packages/psycopg2/__init__.py", line 124, in connect
raise TypeError('missing dsn and no parameters')
TypeError: missing dsn and no parameters

Thank you in advance,
Hans