How to check if PostgreSQL schema exists using SQLAlchemy?

@javax's answer is almost correct; the following is a little clarification:

q = exists(select([("schema_name")]).select_from("information_schema.schemata")
    .where("schema_name = 'foo'"))
if not session.query(q).scalar():
    session.execute('CREATE SCHEMA foo;')

If you want to integrate it with SQLAlchemy you could use reflection but for an easier and quicker solution:

from sqlalchemy.sql import exists, select
exists(select([("schema_name")]).select_from("information_schema.schemata").
       where("schema_name == 'foo'"))

This will return True or False.

I'm using MySQL and this works for me (with sqlalchemy v1.4.1, python 3.9.1):

import sqlalchemy as sa

engine = sa.create_engine("mysql+pymysql://someuser:somepassword@somehost")
inspector = sa.inspect(engine)
myschema = "someschema"
if myschema in inspector.get_schema_names():
    print(f"{myschema} schema exists")

and if you want to create a schema if it doesn't exist:

if myschema not in inspector.get_schema_names():
    engine.execute(sa.schema.CreateSchema(myschema))
    # optional. set the default schema to the new schema:
    engine.dialect.default_schema_name = myschema

I've been using this with Postgres, though was surprised to learn that IF NOT EXISTS is not part of the SQL standard -

engine.execute('CREATE SCHEMA IF NOT EXISTS foo;')

Apparently it's an extension for Postgres and MySQL - https://www.w3resource.com/sql/sql-basic/create-schema.php

This worked for me. Finds if a schema exists using pure SqlAlchemy:

from sqlalchemy import create_engine
from sqlalchemy import event
from sqlalchemy.schema import CreateSchema, DropSchema
...
engine = create_engine(dbstr)
meta = ModelBase()
...
if not engine.dialect.has_schema(engine, schema=schema_name):
    event.listen(meta.metadata, 'before_create', CreateSchema(schema_name))

meta.metadata.reflect(bind=engine, schema=schema_name)
meta.metadata.create_all(engine, checkfirst=True)

SQLAlchemy 2.0 introduced backend-agnostic way to inspect the database state with Inspector object. It has has_schema method to check if schema exists in database.

I usually use this code if I need to create a new schema if it hasn't been yet presented in the database:

from sqlalchemy import create_engine, inspect
from sqlalchemy.schema import CreateSchema

schema = "new_schema"
connectable = create_engine("postgresql+psycopg2://postgres@localhost/postgres")

with connectable.connect() as connection:
    if not inspect(connection).has_schema(schema):
        connection.execute(CreateSchema(schema))
        connection.commit()