Adventures in Machine Learning

Mastering SQLite Database Operations with Python

Creating a Database in Python with SQLite

If you’re a Python programmer, chances are you may have heard of SQLite, a self-contained, serverless, zero-configuration SQL database engine. It’s a popular choice for small-scale applications, particularly in the world of mobile app development.

In this article, we’ll explore how to create a database using Python and SQLite.

Connecting to SQLite Database in Python

The first step in working with SQLite in Python is to connect to the SQLite database using the sqlite3 module. This module provides a standardized Python interface for working with SQLite, making it easy to perform SQL-based database operations.

To connect to an SQLite database using Python, we use the connect() method, which returns a Connection object. The following code demonstrates how to connect to an SQLite database named ‘mydatabase.db’:

import sqlite3

# Connect to database

conn = sqlite3.connect(‘mydatabase.db’)

Once you have the connection object, you can create a cursor object to interact with the database.

Creating a cursor object to execute SQLite queries

The cursor object allows you to execute SQL statements against the SQLite database. You can create a cursor object by calling the cursor() method of the connection object, as shown below:

#Create a cursor object

cursor = conn.cursor()

This object will be used later in executing SQL statements.

Creating a Table in SQLite from Python

Now that we have connected to the database and have our cursor object, we can create tables in the database.

Preparing a create table query

To create a table in SQLite, we use a SQL statement called ‘CREATE TABLE’. The statement takes the following form:

CREATE TABLE table_name (

column1 datatype constraint,

column2 datatype constraint,

column3 datatype constraint,

…. );

Where ‘table_name’ is the name of the table you want to create, ‘column1’, ‘column2’, etc.

are the names of columns in the table, and ‘datatype’ is the data type of each column. The optional ‘constraint’ specifies additional constraints on the column.

For example, a column may require unique data to be inserted into it. The following code demonstrates how to create a table called ‘people’, with columns for name, age, and location:

# Create table

cursor.execute(”’CREATE TABLE people

(name text, age integer, location text)”’)

Executing the query using cursor.execute() method

To execute the SQL query for creating the table, we use the ‘execute’ method on the cursor object, followed by the SQL statement we have prepared.

# commit the transaction

conn.commit()

The table ‘people’ now exists in the database ‘mydatabase.db’.

Conclusion

In this article, we have discussed the steps to create a SQLite database and table using Python. We used the sqlite3 module to establish a connection with the database, then created a cursor object to execute SQL statements.

We prepared a SQL statement to create a table and executed it using the cursor.execute() method. SQLite is a great option for small-scale database applications, and Python makes it easy to work with SQLite databases.

With the above steps, you can create, read, update, and delete data from your SQLite database using Python.

Performing CRUD Operations on SQLite Table

SQLite is a popular choice for small-scale database operations, and Python’s simplicity and ease of use make it an ideal tool for interacting with SQLite databases. In this article, we will discuss how to perform CRUD (Create, Read, Update, and Delete) operations on an SQLite table using Python.

Inserting data into SQLite Table from Python

The first step in populating an SQLite table is to insert data into it using the INSERT command. The syntax for the INSERT command is as follows:

INSERT INTO table_name (column1, column2, column3, …) VALUES (value1, value2, value3, …);

Where table_name is the name of the table, column1, column2, and column3 are the names of the columns in the table, and value1, value2, and value3 are the values to be inserted.

To insert data into an SQLite table from Python, we first prepare the SQL statement, and then we execute it using the cursor object. The following code demonstrates how to insert data into an SQLite table named ‘people’:

#Prepare the query

sql = ”’INSERT INTO people (name, age, location) VALUES (?, ?, ?)”’

#Insert data into the table

cursor.execute(sql, (‘John’, 25, ‘New York’))

#Commit the transaction

conn.commit()

The ‘?’ acts as a placeholder for values that will be supplied later in the execute() method.

Note that we execute the commit() method on the connection object to ensure that the transaction is committed to the database. Reading SQLite Table’s data from Python

To retrieve data from an SQLite table from Python, we use the SELECT query.

We can retrieve all the rows in a table, a set of rows that satisfy a condition, or a specific row using its primary key. To retrieve all the data from an SQLite table, we need to execute the SELECT * FROM table_name SQL statement.

After executing the statement using the cursor object, we can retrieve the data using fetchall(), fetchmany(), or fetchone() methods. The fetchall() method returns all the rows in the result set as a list of tuples.

The fetchmany(n) method returns n rows from the result set as a list of tuples. The fetchone() method returns the next row in the result set as a tuple.

Here’s an example code that demonstrates how to retrieve data from an SQLite table named ‘people’:

#Prepare the SELECT query

sql = ”’SELECT * FROM people”’

#Execute the query

cursor.execute(sql)

#Retrieve the data

rows = cursor.fetchall()

for row in rows:

print(row)

Updating data of SQLite Table from Python

To update data in an SQLite table, we use the UPDATE query. The UPDATE query takes the following form:

UPDATE table_name SET column1=value1, column2=value2, …

WHERE condition;

Where table_name is the name of the table, column1, column2, etc. are the names of the columns to be updated, and value1, value2, etc.

are the new values to be assigned to the columns. The WHERE clause specifies the condition to be satisfied for the rows to be updated.

The following code demonstrates how to update data in the ‘people’ table:

#Prepare the UPDATE query

sql = ”’ UPDATE people SET location = ? WHERE name = ?”’

#Update the data

cursor.execute(sql, (‘Boston’, ‘John’))

#Commit the transaction

conn.commit()

In the code above, we first prepare the query to update the location of the person named John to Boston.

We then execute the query and commit the transaction to the database.

Deleting data from SQLite Table from Python

To delete data from an SQLite table, we use the DELETE query. The DELETE query takes the following form:

DELETE FROM table_name WHERE condition;

Where table_name is the name of the table, and the condition specifies the rows to be deleted.

The following code demonstrates how to delete data from the ‘people’ table:

#Prepare the DELETE query

sql = ”’DELETE FROM people WHERE age > ?”’

#Delete the data

cursor.execute(sql, (20,))

#Commit the transaction

conn.commit()

In the code above, we first prepare the query to delete all people older than 20 years from the ‘people’ table. We then execute the query and commit the transaction to the database.

Executing SQL File from Python

Sometimes, it’s necessary to execute a SQL script instead of individual SQL commands. To execute an SQL file from Python, we use the cursor’s executescript() method.

The following code demonstrates how to execute an SQL script:

#Open the SQL file

file = open(‘script.sql’, ‘r’)

sql = file.read()

#Execute the script

cursor.executescript(sql)

#Commit the transaction

conn.commit()

In the code above, we first read the contents of the SQL file ‘script.sql’. We then execute the queries in the file using the executescript() method on the cursor object, and then we commit the transaction.

Conclusion

In this article, we discussed how to perform CRUD operations on an SQLite table using Python. We used the INSERT, SELECT, UPDATE, and DELETE queries to create, read, update, and delete data from the ‘people’ table.

We also explored how to execute an SQL script using the executescript() method on the cursor object. By following these steps, you can interact with an SQLite database using Python and perform various operations on the database.

Inserting/Retrieving Files from SQLite Table in Python

SQLite is a popular choice for small-scale database operations, and Python’s simplicity and ease of use make it an ideal tool for interacting with SQLite databases. In this article, we will discuss how to insert and retrieve files in an SQLite table using Python.

Inserting digital data as BLOB into SQLite Table from Python

One of the major advantages of SQLite is that it’s capable of handling and storing digital data, such as images and audio files, as a Binary Large Object (BLOB) in a table. To store digital data in an SQLite table, we need to create a BLOB column in the table.

To insert a file in the table, we first need to read the contents of the file into memory. We can then use the sqlite3.Binary() method to convert the contents to a BLOB object, which we can then insert into a BLOB column in the SQL query.

The following code demonstrates how to insert a file named ‘audio.mp3’ in an SQLite table named ‘files’:

#Open file in read mode

with open(“audio.mp3”, “rb”) as file:

#Read file contents

data = file.read()

#Prepare the INSERT query

sql = ”’INSERT INTO files(name, data) VALUES(?,?)”’

#Convert data to BLOB object

blob_data = sqlite3.Binary(data)

#Insert data into the table

cursor.execute(sql, (‘audio’, blob_data))

#Commit the transaction

conn.commit()

In the code above, we first read the contents of the ‘audio.mp3’ file into memory using the read() method. We then prepare the INSERT query to insert the file name and data into the ‘files’ table.

Finally, we convert the file data into a BLOB object using the sqlite3.Binary() method and insert it into the table.

Retrieving digital data from SQLite Table in Python

To retrieve a file from an SQLite table, we can use the SELECT query and the fetchone() method. The SELECT query fetches the data of a specific row, while the fetchone() method fetches the first row of the result set.

The following code demonstrates how to retrieve a file from the ‘files’ table:

#Prepare the SELECT query

sql = ”’SELECT data FROM files WHERE name = ?”’

#Execute the query

cursor.execute(sql, (‘audio’,))

#Retrieve the data

row = cursor.fetchone()

#Save the data to file

with open(‘output.mp3’, ‘wb’) as output_file:

output_file.write(row[0])

In the code above, we prepare the SELECT query to retrieve the data of a file with the name ‘audio’. After executing the query and fetching the first row using fetchone(), we save the data to a file named ‘output.mp3’.

Note that the data returned by fetchone() is a tuple, and so we access the data using the index of the first element in the tuple.

Working with SQLite Date and Timestamp Types in Python and vice-versa

SQLite has built-in support for date and timestamp data types. In order to handle these types in an SQLite table from Python, we will need to use a Python module called datetime.

In Python, we can create a datetime object by importing the datetime module and using the datetime() constructor. We can then convert the datetime object to a string using str() method or a specific format using strftime() method for adding to an SQLite table.

The following code demonstrates how to add a date to an SQLite table using Python:

#Import datetime module

import datetime

#Current date

today = datetime.datetime.now()

#Prepare the INSERT query

sql = ”’INSERT INTO date_table(date) VALUES(?)”’

#Convert date as string

date_str = today.strftime(“%d-%m-%Y”)

#Insert data into the table

cursor.execute(sql, (date_str,))

#Commit the transaction

conn.commit()

In the code above, we first import the datetime module and initialize a datetime object with the current date and time using the now() method. We then prepare the INSERT query to insert the date into a table named ‘date_table’.

Finally, we use the strftime() method to convert the datetime object into a string formatted in the “dd-mm-yyyy” format. To retrieve dates from the SQLite table, we can use the SELECT query and the fetchone() method.

The SELECT query fetches the data of a specific row, while the fetchone() method fetches the first row of the result set. The following code demonstrates how to retrieve dates from the ‘date_table’ table:

#Prepare the SELECT query

sql = ”’SELECT date FROM date_table”’

#Execute the query

cursor.execute(sql)

#Retrieve the data

rows = cursor.fetchall()

for row in rows:

print(row[0])

The above code displays all the dates in the ‘date_table’ table.

When retrieving dates, we use row[0] to get the first column value.

Conclusion

In this article, we discussed how to insert and retrieve files, as well as how to work with SQLite date and timestamp types in Python. We used the Binary Large Object (BLOB) data type to store files in SQLite tables, while the datetime module was used to manipulate date and time data.

By following these steps, you can easily insert and retrieve data from SQLite tables and manipulate SQLite date and timestamp values.

SQLite Database Exceptions

As with any software, things can go wrong when working with SQLite databases in Python. In order to identify and handle any errors or exceptions thrown by SQLite in Python, we will need to use exception handling.

This is done using a try-except-finally block.

Identifying SQLite Database exceptions and taking corrective actions

When working with databases, it’s common to encounter exceptions such as OperationalError, IntegrityError, ProgrammingError, and others. These are all examples of exceptions raised by SQLite when it encounters an error or issue with the database.

When an exception is raised, it’s important to take corrective action based on the type of exception. This might include retrying the operation, providing an alternative solution, or gracefully handling the error and notifying the user.

Here’s an example of how to use a try-except block when executing an SQL command with SQLite in Python:

try:

# Execute SQL command here

cursor.execute(sql_command)

except sqlite3.Error as e:

# Handle the exception here

print(“An error occurred:”, e.args[0])

finally:

# Close the database connection here

conn.close()

In the code above, the try block contains the code that might raise an exception. The except block catches the exception and handles it by displaying an error message.

The finally block ensures that the database connection is closed, regardless of whether an exception was raised or not.

Changing SQLite Connection Timeout when Connecting from Python

When working with SQLite databases, there may be instances where you need to modify the timeout value for the connection. If a connection is idle for a certain amount of time, SQLite will automatically close it.

This can cause unexpected behavior if there are long-running operations that need to keep the connection active. Fortunately, it’s easy to modify the timeout value when connecting to an SQLite database from Python.

All you need to do is pass the “timeout” parameter with the desired value in seconds when creating the connection. Here’s an example of how to specify the timeout value when connecting to an SQLite database in Python:

import sqlite3

# Set the timeout value to 30 seconds

conn = sqlite3.connect(‘mydatabase.db’, timeout=30)

In the code above, we specify a timeout value of 30 seconds by passing the timeout parameter with the value of 30 when calling the connect() method. It’s important to note that the timeout value only applies to a single connection.

If you need to modify the timeout value for multiple connections, you will need to set it for each connection separately.

Conclusion

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