Python check for NULL values from user input and do not include in sql update

Question

In my function I am asking for input from the user for different variables and then updating the DB. The issue is if they do not input anything is there a way I can not push anything to the DB? At the moment when they do not enter a value for the var, the value in the DB will get wiped out.

db_root = '/var/lib/mysql/'

db_to_create = 'students'
db_to_use = 'students'

conn = pymysql.connect(host='localhost',  user='root', passwd='dbadmin',  cursorclass=pymysql.cursors.DictCursor)

print('Connection successful!!')


def modify_student():
    student_id = input("Enter the id of the student record you wish to modify: ")
    student_info = input("Is this student personal information you want to modify - y or n: ")
    if student_info == 'y':
        firstname = input("Enter the first name: ")
        lastname = input("Enter the last name: ")
        email = input("Enter the email address: ")
        address = input("Enter the address: ")
        DOB = input("Enter the DOB in YYYY-MM-DD: ")

        cur = conn.cursor()
        command = "use %s; " %db_to_use
        cur.execute(command)

        sql = "UPDATE students_info SET firstname = %s, lastname = %s,  email = %s,  address = %s,  DOB = %s  WHERE ID = %s;"
        cur.execute(sql, [firstname, lastname, email, address, DOB, student_id])

        print(cur.execute)
        conn.commit()
        cur.close()
        conn.close()
    else:
        print("else")

modify_student()

######## SCHEMA ##################

        MariaDB [students]> DESCRIBE students_info;
    +-----------+--------------+------+-----+---------+----------------+
    | Field     | Type         | Null | Key | Default | Extra          |
    +-----------+--------------+------+-----+---------+----------------+
    | ID        | int(11)      | NO   | PRI | NULL    | auto_increment |
    | firstname | varchar(255) | YES  |     | NULL    |                |
    | lastname  | varchar(255) | YES  |     | NULL    |                |
    | email     | varchar(255) | YES  |     | NULL    |                |
    | address   | varchar(255) | YES  |     | NULL    |                |
    | DOB       | date         | YES  |     | NULL    |                |
    | english   | varchar(255) | YES  |     | NULL    |                |
    | maths     | varchar(255) | YES  |     | NULL    |                |
    | history   | varchar(255) | YES  |     | NULL    |                |
    | science   | varchar(255) | YES  |     | NULL    |                |
    +-----------+--------------+------+-----+---------+----------------+

Check each input value for not being an empty string "". If any of them is an empty string, do not push the updates. — DYZ
– DYZ, Commented Aug 3, 2018 at 0:56

blhsing · Accepted Answer · 2018-08-03 01:21:14Z

1

You can use the following helper function:

def mandatory_input(prompt):
    while True:
        value = input(prompt)
        if value:
            return value
        print("You did not enter the required information.")

And replace all the input prompts that are deemed mandatory with it, so:

student_id = input("Enter the id of the student record you wish to modify: ")

becomes:

student_id = mandatory_input("Enter the id of the student record you wish to modify: ")

and so on, so that the user will be kept being prompted for a value until they enter something.

answered Aug 3, 2018 at 1:21

blhsing

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Oudeis · Accepted Answer · 2018-08-03 01:24:06Z

1

In addition, if you want to wait for the user to finish, and then validate when they've entered at the end:

if all([firstname, lastname, email, ...]):
    cur = conn.cursor()
    ...
else:
    print('User missed an input')

answered Aug 3, 2018 at 1:24

Oudeis

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