How to read and insert bytea columns using psycopg2?

Question

I am working on a Python script to replicate some Postgresql tables from one environment to another (which does a little more than pg_dump

Answer 1

If you have this database structure:

CREATE TABLE test (a bytea,
                   b int,
                   c text)

then inserting binary data into the request can be done like so, without any wrappers:

bin_data = b'bytes object'
db = psycopg2.connect(*args)  # DB-API 2.0
c = db.cursor()
c.execute('''INSERT INTO test VALUES (%s, %s, %s)''', (bin_data, 1337, 'foo'))
c.execute('''UPDATE test SET a = %s''', (bin_data + b'1',))

Then, when you query it:

c.execute('''SELECT a FROM test''')

You'll receive a memoryview, which is easily converted back to bytes:

mview = c.fetchone()
new_bin_data = bytes(mview)
print(new_bin_data)

Output: b'bytes object1'

Also, I'd suggest you not to assemble queries by string formatting. psycopg2's built-in parameter substitution is much more convenient and you don't have to worry about validating data to protect from SQL injections.