Psycopg2.interfaceerror: cursor already closed

The error psycopg2.InterfaceError: cursor already closed occurs when you try to access a cursor object that has already been closed or no longer exists.

Here’s an example to understand this error:

import psycopg2

# Establish a connection to the database
conn = psycopg2.connect(database="mydatabase", user="myuser", password="mypassword", host="localhost", port="5432")

# Create a cursor
cursor = conn.cursor()

# Execute a query
cursor.execute("SELECT * FROM mytable")

# Close the cursor
cursor.close()

# Try to access the cursor after closing
cursor.execute("SELECT * FROM mytable")  # This line will cause the error

In the above example, we establish a connection to a PostgreSQL database and create a cursor. We then execute a query using the cursor and close it. After closing the cursor, we try to execute another query using the same cursor, which results in the psycopg2.InterfaceError: cursor already closed error.

To fix this error, you need to create a new cursor or re-use an existing one before executing any further queries. Here’s an updated example:

import psycopg2

# Establish a connection to the database
conn = psycopg2.connect(database="mydatabase", user="myuser", password="mypassword", host="localhost", port="5432")

# Create a cursor
cursor = conn.cursor()

# Execute a query
cursor.execute("SELECT * FROM mytable")

# Close the cursor
cursor.close()

# Create a new cursor
new_cursor = conn.cursor()

# Execute another query using the new cursor
new_cursor.execute("SELECT * FROM myothertable")

# Fetch results and process them
results = new_cursor.fetchall()
for row in results:
    print(row)

# Close the new cursor
new_cursor.close()

# Close the connection
conn.close()

In this updated example, we create a new cursor new_cursor after closing the initial cursor. We then execute another query using the new cursor and fetch the results for processing. Finally, we close the new cursor and close the connection to the database.