For loops - Python

For i in range(n):

Let’s say we wanted to print out the word “Hello” 3 times, we could just call the print() function 3 times, like this:

	print("hello")
	print("hello")
	print("hello")

view raw print3timeshardway.py hosted with

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This is nice and easy, and is fine if you just want to do it 3 times – but what if you need to repeat the print statement 10 times, or 100 times? Hmmm this is starting to become hard work – surely there must be a easier way?

We can use a for loop!

	for i in range(3):
	print("hello")

view raw print3timestheeasyway.py hosted with

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(Notice that the line of code that is to be repeated is indented(has 4 spacers before it, this is your way of telling the computer that you want to repeat these lines of code)

But this is only one line of code less that the line above and requires a bit of extra thinking – is it really worth it? Well in this instance it probably isn’t, but what about that 100 times repeat?

	for i in range(100):
	print("hello")

view raw print100times.py hosted with

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Now the efficiency ( and readability) or loops really comes in to play.

Practice:

Have a go at the following practice examples:

Practice 1

Practice 2

Practice 3

Keeping count

Breaking out of a look

Sometimes we want to stop looping through a for loop if a variable achieves a certain value or if an event happens. In this situation we need to use the break statement.

	for i in range(100):
	choice = input("Do you want to stop now?")
	if choice == "yes":
	break
	print("Goodbye then!")

view raw forloopbreakexample.py hosted with

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Super simple!

Example

Here is a slightly longer example

	#Simple darts game
	#Each player gets 6 attempts to score as close to 180 as possible.
	#If your total is over 180 you are bust and you lose
	import os

	total = 0
	for i in range(6):
	os.system('clear')
	print("Current score - " +str(total) + "\n\n")

	score = int(input("What did you score for dart" +str(i+1) + "?"))
	print("\n\n")
	total += score
	if total > 180:
	print("You're bust, game over!!!!!!")
	break


	if total <= 180:
	print("Your end score is" + str(180-total))