How to compare last value to new value?

Question

Goal:

I am aiming to compare the last result to new result, every time the function runs.

Code:

starttime = time.time()

def countRows():
    while True:
        #Get number of rows from SQL table
        sqlCursor = sqlConnection.cursor()

        sqlCursor.execute("Select count(*) from SalesOrder")

        rowcount = sqlCursor.fetchone()[0]

        print(rowcount)

        if rowcount != rowcount:
            print("changed")

        time.sleep(10.0 - ((time.time() - starttime) % 10.0))

countRows()

Details:

Here I am getting count from SQL table.

This is the output every 10 seconds:

1000
1000
1000
1000

If a record is added to sql table, the count obviously changes to 1001.

Problem with current code:

The if statement does not work - when the number changes. It just prints the number.

Question:

Whilst the function is running every 10 seconds. How can I trigger print("changed") if the value is not same as previous value?

Answer 1

you are comparing the same variable with itself:

if rowcount != rowcount:

you should use an intermediate variable to store the previous count: something like:

prev_rowcount = None
...
if prev_rowcount != None and prev_rowcount != rowcount:
    print("changed")
prev_rowcount = rowcount

Answer 2

Think this will work:

starttime = time.time()

def countRows():
    prev_rowcount = None
    while True:
        #Get number of rows from SQL table
        sqlCursor = sqlConnection.cursor()

        sqlCursor.execute("Select count(*) from SalesOrder")

        rowcount = sqlCursor.fetchone()[0]

        print(rowcount)

        if rowcount != prev_rowcount and prev_rowcount != None:
            print("changed")
        prev_rowcount = rowcount
        time.sleep(10.0 - ((time.time() - starttime) % 10.0))

countRows()