YouTipRef Random Randrange
## Python random.randrange() Method
The `random.randrange()` method is a built-in function in Python's `random` module. It returns a randomly selected element from a specified range of integers.
This method is highly efficient and behaves similarly to Python's built-in `range()` function, but instead of returning a sequence, it returns a single random integer from that sequence.
---
### Syntax
```python
random.randrange(start, stop, step)
```
#### Parameter Values
| Parameter | Type | Required/Optional | Description |
| :--- | :--- | :--- | :--- |
| **`start`** | Integer | Optional | Specifies the starting value of the range. Defaults to `0` if omitted. |
| **`stop`** | Integer | Required | Specifies the exclusive upper limit of the range. The returned value will always be less than this number. |
| **`step`** | Integer | Optional | Specifies the incrementation between numbers in the range. Defaults to `1` if omitted. |
#### Return Value
* Returns a single **integer** chosen randomly from the specified range.
---
### Code Examples
#### Example 1: Basic Usage (Generate a number between 1 and 8)
The following example returns a random integer from `1` up to (but not including) `9` (i.e., $1 \le x < 9$).
```python
import random
# Generate a random number between 1 and 8
result = random.randrange(1, 9)
print(result)
```
**Possible Output:**
```text
8
```
#### Example 2: Using Only the `stop` Parameter
If you provide only one argument, it is treated as the `stop` value. The range will start from `0` with a step of `1`.
```python
import random
# Generate a random number from 0 to 9 (10 is excluded)
result = random.randrange(10)
print(result)
```
**Possible Output:**
```text
4
```
#### Example 3: Using the `step` Parameter
You can use the `step` parameter to generate random numbers that follow a specific pattern, such as even numbers, odd numbers, or multiples of five.
```python
import random
# Generate a random even number between 0 and 100 (inclusive of 0, exclusive of 100)
even_num = random.randrange(0, 100, 2)
print(f"Random even number: {even_num}")
# Generate a random multiple of 5 between 5 and 50 (exclusive of 50)
multiple_of_five = random.randrange(5, 50, 5)
print(f"Random multiple of 5: {multiple_of_five}")
```
**Possible Output:**
```text
Random even number: 42
Random multiple of 5: 35
```
---
### Considerations & Best Practices
1. **Exclusive Upper Bound (`stop`):**
The `stop` value is **never** included in the possible outcomes. For example, `random.randrange(1, 5)` can only return `1`, `2`, `3`, or `4`.
2. **`random.randrange()` vs `random.randint()`:**
* `random.randrange(start, stop)` does **not** include the `stop` value (exclusive).
* `random.randint(start, stop)` **includes** the `stop` value (inclusive). Under the hood, `random.randint(a, b)` is equivalent to `random.randrange(a, b + 1)`.
* `random.randrange()` supports a `step` argument, whereas `random.randint()` does not.
3. **ValueError:**
If the range is empty (for example, if `start` is greater than `stop` and the `step` is positive, e.g., `random.randrange(10, 1)`), Python will raise a `ValueError: empty range for randrange()`.