Build a Python App with CockroachDB - cockroachdb

This tutorial shows you how build a simple Python application with CockroachDB using a PostgreSQL-compatible driver or ORM.

We have tested the Python psycopg2 driver and the SQLAlchemy ORM enough to claim beta-level support, so those are featured here. If you encounter problems, please open an issue with details to help us make progress toward full support.

Before you begin

Install CockroachDB.
Start up a secure or insecure local cluster.
Choose the instructions that correspond to whether your cluster is secure or insecure:

Step 1. Install the psycopg2 driver

To install the Python psycopg2 driver, run the following command:

$ pip install psycopg2

For other ways to install psycopg2, see the official documentation.

## Step 2. Create the `maxroach` user and `bank` database {% include {{page.version.version}}/app/create-maxroach-user-and-bank-database.md %} ## Step 3. Generate a certificate for the `maxroach` user Create a certificate and key for the `maxroach` user by running the following command. The code samples will run as this user. {% include copy-clipboard.html %} ~~~ shell $ cockroach cert create-client maxroach --certs-dir=certs --ca-key=my-safe-directory/ca.key ~~~ ## Step 4. Run the Python code Now that you have a database and a user, you'll run the code shown below to: - Create a table and insert some rows - Read and update values as an atomic [transaction](transactions.html) ### Basic statements First, use the following code to connect as the `maxroach` user and execute some basic SQL statements, creating a table, inserting rows, and reading and printing the rows. Download the basic-sample.py file, or create the file yourself and copy the code into it. {% include copy-clipboard.html %} ~~~ python {% include {{page.version.version}}/app/basic-sample.py %} ~~~ Then run the code: {% include copy-clipboard.html %} ~~~ shell $ python basic-sample.py ~~~ The output should be: ~~~ Initial balances: ['1', '1000'] ['2', '250'] ~~~ ### Transaction (with retry logic) Next, use the following code to again connect as the `maxroach` user but this time execute a batch of statements as an atomic transaction to transfer funds from one account to another, where all included statements are either committed or aborted. Download the txn-sample.py file, or create the file yourself and copy the code into it. {{site.data.alerts.callout_info}}CockroachDB may require the client to retry a transaction in case of read/write contention. CockroachDB provides a generic retry function that runs inside a transaction and retries it as needed. You can copy and paste the retry function from here into your code.{{site.data.alerts.end}} {% include copy-clipboard.html %} ~~~ python {% include {{page.version.version}}/app/txn-sample.py %} ~~~ Then run the code: {% include copy-clipboard.html %} ~~~ shell $ python txn-sample.py ~~~ The output should be: ~~~ Balances after transfer: ['1', '900'] ['2', '350'] ~~~ To verify that funds were transferred from one account to another, start the [built-in SQL client](use-the-built-in-sql-client.html): {% include copy-clipboard.html %} ~~~ shell $ cockroach sql --certs-dir=certs --database=bank ~~~ To check the account balances, issue the following statement: {% include copy-clipboard.html %} ~~~ sql > SELECT id, balance FROM accounts; ~~~ ~~~ +----+---------+ | id | balance | +----+---------+ | 1 | 900 | | 2 | 350 | +----+---------+ (2 rows) ~~~

## Step 2. Create the `maxroach` user and `bank` database {% include {{page.version.version}}/app/insecure/create-maxroach-user-and-bank-database.md %} ## Step 3. Run the Python code Now that you have a database and a user, you'll run the code shown below to: - Create a table and insert some rows - Read and update values as an atomic [transaction](transactions.html) ### Basic statements First, use the following code to connect as the `maxroach` user and execute some basic SQL statements, creating a table, inserting rows, and reading and printing the rows. Download the basic-sample.py file, or create the file yourself and copy the code into it. {% include copy-clipboard.html %} ~~~ python {% include {{page.version.version}}/app/insecure/basic-sample.py %} ~~~ Then run the code: {% include copy-clipboard.html %} ~~~ shell $ python basic-sample.py ~~~ The output should be: ~~~ Initial balances: ['1', '1000'] ['2', '250'] ~~~ ### Transaction (with retry logic) Next, use the following code to again connect as the `maxroach` user but this time execute a batch of statements as an atomic transaction to transfer funds from one account to another, where all included statements are either committed or aborted. Download the txn-sample.py file, or create the file yourself and copy the code into it. {{site.data.alerts.callout_info}}CockroachDB may require the client to retry a transaction in case of read/write contention. CockroachDB provides a generic retry function that runs inside a transaction and retries it as needed. You can copy and paste the retry function from here into your code.{{site.data.alerts.end}} {% include copy-clipboard.html %} ~~~ python {% include {{page.version.version}}/app/insecure/txn-sample.py %} ~~~ Then run the code: {% include copy-clipboard.html %} ~~~ shell $ python txn-sample.py ~~~ The output should be: ~~~ Balances after transfer: ['1', '900'] ['2', '350'] ~~~ To verify that funds were transferred from one account to another, start the [built-in SQL client](use-the-built-in-sql-client.html): {% include copy-clipboard.html %} ~~~ shell $ cockroach sql --insecure --database=bank ~~~ To check the account balances, issue the following statement: {% include copy-clipboard.html %} ~~~ sql > SELECT id, balance FROM accounts; ~~~ ~~~ +----+---------+ | id | balance | +----+---------+ | 1 | 900 | | 2 | 350 | +----+---------+ (2 rows) ~~~

What's next?

Read more about using the Python psycopg2 driver.

You might also be interested in using a local cluster to explore the following CockroachDB benefits: