sqlalchemy.exc.NoSuchModuleError: Can't load plugin: sqlalchemy.dialects:postgres

# sqlalchemy.exc.NoSuchModuleError: Can't load plugin: sqlalchemy.dialects:postgres

The error "sqlalchemy.exc.NoSuchModuleError: Can't load plugin: sqlalchemy.dialects:postgres" occurs when we use the outdated postgres dialect in a connection URL.

To solve the error, use the dialect postgresql in your connection URL instead.

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File "/home/borislav/Desktop/bobbyhadz_python/venv2/lib/python3.10/site-packages/sqlalchemy/util/langhelpers.py", line 343, in load
    raise exc.NoSuchModuleError(
sqlalchemy.exc.NoSuchModuleError: Can't load plugin: sqlalchemy.dialects:postgres

Here is an example of how the error occurs.

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from flask import Flask
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)

# ⛔️ Using postgres:// dialect
app.config["SQLALCHEMY_DATABASE_URI"] = "postgres://username@localhost:5432/exampledb"

db = SQLAlchemy(app)

# Use the postgresql dialect instead

To solve the error, use the postgresql dialect instead.

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from flask import Flask
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)

# ✅ Using postgresql:// dialect
app.config["SQLALCHEMY_DATABASE_URI"] = "postgresql://username@localhost:5432/exampledb"

db = SQLAlchemy(app)

print(db)

Make sure you don't have 2 s characters next to one another in the string postgresql.

Database URLs use the following format.

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dialect://username:password@host:port/database

Username, password, host and port are optional depending on the database type and configuration.

Your connection string for PostgreSQL might look something like this.

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postgresql://bobbyhadz:password@localhost:5432/mydatabase

The database URL should start with postgresql://, not with postgres:// as SQLAlchemy v1.4 has removed support for the deprecated postgres dialect.

If you get the error ModuleNotFoundError: No module named 'flask', click on the link and follow the instructions.

# Using the str.replace() method to correct the string

If you have the URL stored in a string or if you get the URL using an environment variable, you can use the str.replace() method to make sure you specify the postgresql dialect instead of postgres.

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# ⛔️ Incorrect URL (postgres dialect)
DATABASE_URL = "postgres://username@localhost:5432/exampledb"

# ✅ Correct URL (postgresql dialect)
DATABASE_URL = DATABASE_URL.replace(
    'postgres://',
    'postgresql://',
    1
)

# 👇️ postgresql://username@localhost:5432/exampledb
print(DATABASE_URL)

This approach would work if you get the database URL via an environment variable (e.g. on Heroku).

If the string postgres:// is not contained in your database URL, then nothing is replaced.

Here is an example that loads the DATABASE_URL from an environment variable and replaces the substring.

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import os

uri = os.getenv("DATABASE_URL")
if uri.startswith("postgres://"):
    uri = uri.replace("postgres://", "postgresql://", 1)

# The rest of the connection code

The code sample is suitable for a Heroku environment and assumes that you have a DATABASE_URL environment variable.

The str.replace method returns a copy of the string with all occurrences of a substring replaced by the provided replacement.

The method takes the following parameters:

The method doesn't change the original string. Strings are immutable in Python.

# Additional Resources

You can learn more about the related topics by checking out the following tutorials:

• ModuleNotFoundError No module named 'sqlalchemy' in Python
• ModuleNotFoundError: No module named 'flask' in Python