More on Range

In one example from the last section, we used range to make the loop run four times:

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for num in range(4):
   print(num)
   print("Hello" * num)

For each iteration, the variable num took on a new value (0, 1, 2, or 3).

What if we wanted the loop to use the sequence 1, 2, 3, 4 instead?

Set Start and Stop Values

Whenever we use range(value) in a for statement, Python always begins counting with 0. To start counting at a different number, we need to include that value inside the () in addition to a stop value.

Instead of range(value), a more detailed version of the keyword is range(start_value, stop_value). The starting value is included in the counting for the loop, but the stop value is not.

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for num in range (start_value, stop_value):
   # do something...

If we replaced line 1 in the code above with for num in range(1, 5), then the loop variable num would take values of 1, 2, 3, and 4.

Now, what if we want to count DOWN from one value to another or change the loop variable by more than a single unit each iteration?

Set a Step Value

Suppose we want our loop variable to only be a set of even numbers (e.g. 0, 2, 4, 6…). We want to begin counting at 0 and then increase the loop variable by 2 units instead of 1.

To make this happen, we need to add one more value inside range. This is called the step value.

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for num in range(start_value, stop_value, step_value):
   # do something ...

for num in range(0, 21, 2)

for num in range(0, 21, 5)

for num in range(50, 39, -1)   # Counts from 50 down to 40

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