 # Python range()

The built-in function range() is used to return a sequence of integer numbers by specifying starting and ending points in the sequence. This resultant sequence is immutable means values cannot be changed. For repeating a  task a specific number of times we can use this range() method with loops.

``````
range(stop)
range(start, stop[, step]) #where stop is an integer indicates stop position.
```
```

## range() Parameters:

Takes three parameters. If the start index is not given it starts from 0, and it will increment the value by 1 continue until the stop index.

Parameter Description Required / Optional
start  An integer number specifying at which position to start. Default is 0 optional
stop  An integer number specifying at which position to stop Required
step  An integer determines the increment between each integer in the sequence optional

## range() Return Value

The result sequence is starting from 0 to stop - 1.if the stop is negative or 0 it returns an empty sequence.

r[n] = start + step*n (for both positive and negative step)
where, n >=0 and r[n] < stop (positive step)
where, n >= 0 and r[n] > stop (negative step)

If the step is zero it raises a ValueError exception. If non zero it returns a sequence according to the formula. If it doesn't meet the value constraint, an empty sequence is returned.

Input Return Value
integer  integer sequence

## Examples of range() method in Python

### Example 1: How range works in Python?

``````
# empty range
print(list(range(0)))

# using range(stop)
print(list(range(10)))

# using range(start, stop)
print(list(range(1, 10)))
```
```

Output:

```[]
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
[1, 2, 3, 4, 5, 6, 7, 8, 9]```

### Example 2: Create a list of even number between the given numbers using range()

``````
start = 2
stop = 14
step = 2

print(list(range(start, stop, step)))
```
```

Output:

```[2, 4, 6, 8, 10, 12]
```

### Example 3: How range() works with negative step?

``````
start = 2
stop = -14
step = -2

print(list(range(start, stop, step)))

# value constraint not met
print(list(range(start, 14, step)))
```
```

Output:

```[2, 0, -2, -4, -6, -8, -10, -12]
[]
```
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