Execute statement every N iterations in Python

How about keeping a counter and resetting it to zero when you reach the wanted number? Adding and checking equality is faster than modulo.

printcounter = 0

# Whatever a while loop is in Python
while (...):   
    ...
    if (printcounter == 1000000):
        print('Progress report...')
        printcounter = 0
    ...
    printcounter += 1

Although it's quite possible that the compiler is doing some sort of optimization like this for you already... but this may give you some peace of mind.


Is it really slowing down? You have to try and see for yourself. It won't be much of a slowdown, but if we're talking about nanoseconds it may be considerable. Alternatively you can convert one 10 million loop to two smaller loops:

m = 1000000
for i in range(10):
    for i in range(m):
        // do sth
    print("Progress report")

1. Human-language declarations for x and n:

let x be the number of iterations that have been examined at a given time. let n be the multiple of iterations upon which your code will execute.

2. What we're doing:

The first code block (Block A) uses only one variable, x (defined above), and uses 5 (an integer) rather than the variable n (defined above).

The second code block (Block B) uses both of the variables (x and n) that are defined above. The integer, 5, will be replaced by the variable, n. So, Block B literally performs an action at each nth iteration.

Our goal is to do something every xth iteration and every 5th/nth iteration. We are going through 100 iterations.

m. Easy-to-understand code:

Block A, minimal variables:

for x in 100:
    #what to do every time (100 times): replace this line with your every-iteration functions.
    if x % 5 == 0:
        #what to do every 5th time: replace this line with your nth-iteration functions.

Block B, generalization.

n = 5
for x in 100:
    #what to do every time (100 times): replace this line with your every-iteration functions.
    if x % n == 0:
        #what to do every 5th time: replace this line with your nth-iteration functions.

Please, let me know if you have any issues because I haven't had time to test it after writing it here.

3. Exercises

  1. If you've done this properly, see if you can use it with the turtle.Pen() and turtle.forward() function.
  2. See if you can use this program with the turtle.circle() function.
  3. Check out the reading (seen below) to attempt to improve the programs from exercise 1 and 2.

About modulo and other basic operators: https://docs.python.org/2/library/stdtypes.html http://www.tutorialspoint.com/python/python_basic_operators.htm

About turtle: https://docs.python.org/2/library/turtle.html https://michael0x2a.com/blog/turtle-examples

Tags:

Python

Loops

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