For Loops

For Loops

In programming we have something called a loop. A loop will continue to run (or loop) while a certain condition is satisfied. We can use a for loop when we want to loop (or repeat something) a known amount of times.

When we set up a for loop it looks something like this:

for x in range(10):
    print(x)

We use the keyword for to declare that we are creating a loop. Then we define a variable (in this case x) which is going to be our "counter". We then type the keyword in followed by a range.

Range is a function in python that allows us to start at a number and count up to a certain number while increasing by any interval we want. The basic syntax for the range function looks something like this:

range(start, stop, step)

range(10)  # When only one number is in the function it means we start at 0 
# increase by one each time and stop when our variable hits 10

range(5,10)  # When two numbers are in the function it means to start at the first number (in this case 5) 
# increase by one each time and stop when our variable hits the second number (in this case 10)

range(1,5,2)  # when three numbers are in the function it means to start at the first number (1)
# stop at the second number (5)
# and increase by the last number (2) 

Examples

Some examples may help to illustrate this:

for x in range(4):
    # we are starting at 0, increasing by 1 and stopping at 4
    print(x)

# The output for this will look like
0
1
2
3
# Since we stop at 4 we do not print 4


for i in range(0,6,2):
    # we are starting at 0, increasing by 2 and stopping at 6
    print(i)

# The output for this will look like
0
2
4