Python subprocess (shell=True), not working for postgres command - linux

Question

Using the command line, I confirm that the following commands executes correctly
echo '\c mydatabase;\i db-reset.sql' | psql -U postgres -h localhost
However, in Python, I can confirm that the following lines do absolutely nothing, and return an status code of 0.
import subprocess
code = subprocess.call(r"echo '\c mydatabase;\i db-reset.sql' | psql -U postgres -h localhost", shell=True)
assert code == 0 # This comes to true
Essentially, why is the command invoked using subprocess not actually doing anything?

Answer 1

It works, but you need more backslashes.
Also, I would recommend you don't use shell=True here.
That is what you do, but without shell:
p = subprocess.Popen(['psql', '-U', 'postgres', '-h', 'localhost'], shell=False, stdin=subprocess.PIPE)
p.communicate(r"\c mydatabase;\i db-reset.sql")

Answer 2

Igor has the right approach without a doubt - though it'd be a good idea to close the session afterwards. However, there's a bigger picture issue here, which is that you should not generally be invoking psql to communicate with PostgreSQL from Python.
Use the psycopg2 module, which is widespread and available almost everywhere, to talk to PostgreSQL directly. This will immensely simplify your database communications.
For cases where you actually need psql, like running scripts, please use psql -f and a database argument. Your command in this case should be:
try:
subprocess.check_call([
'psql', '-q',
'-U', 'postgres',
'-h', 'localhost',
'-f', 'db-reset.sql',
'mydatabase'
])
except subprocess.CalledProcessError, ex:
print("Failed to invoke psql: {0}".format(ex))
... or even better, use check_output if you're on a new enough Python version, so you capture error output too. Note the -q (quiet mode) flag, too.
(Note that subprocess will do its own escaping when you're running on a platform like Windows where there's no sensible execv variant system calls or equivalents. So you don't need to care about painful shell escaping quirks.)