NameError: name 'xrange' is not defined in Python
Tags: python, abotwrotethis
Published: 2023-04-14 09:35:02

If you are a Python programmer, you might have come across an error that says "NameError: name 'xrange' is not defined". This error message occurs when you try to use the `xrange()` function in Python 3 or above. In this blog post, we'll delve into what `xrange()` is, why it is not available in Python 3 or higher, and what you can use instead of `xrange()`.

## What is xrange()?

`xrange()` is a built-in function in Python 2 that generates a sequence of numbers to be used in for loops. It is similar to the `range()` function, but instead of returning a list, it returns an object that generates the numbers on the fly. This means that `xrange()` is more memory-efficient than `range()` since it does not generate the numbers in the sequence until they are actually needed.

The syntax for `xrange()` is as follows:

```python
xrange(stop)
xrange(start, stop[, step])
```

Here, `stop` is the number at which the sequence will end, while `start` is the number at which the sequence will begin. If you omit `start`, the sequence will start at `0`. If you omit `step`, the sequence will increment by `1` each time. 

## Why is xrange() not Available in Python 3 or Higher?

In Python 3 and higher, `xrange()` has been removed and replaced with the `range()` function. The main reason for this change is that `range()` in Python 3 behaves like `xrange()` in Python 2. In Python 2, `range()` actually generates a list of numbers, which can be very memory-intensive for large sequences. 

Also, since Python 3 is not backwards-compatible with Python 2, Python developers decided to get rid of `xrange()` to avoid confusion and encourage the use of the more efficient `range()` function.

## What can you use Instead of xrange()?

If you are using Python 3 or higher and need to generate a sequence of numbers, you can use the `range()` function instead of `xrange()`. The syntax for `range()` is similar to that of `xrange()`, as shown here:

```python
range(stop)
range(start, stop[, step])
```

The difference is that `range()` returns a sequence of numbers in the form of a list. If you need to conserve memory, you can use a technique called generators to generate the sequence on-the-fly, just like `xrange()` did. A generator is a function that behaves like an iterator, which means it can be used in a for loop or any other function that expects an iterable object.

Here's an example of a generator function that generates the same sequence of numbers as `xrange(10)`:

```python
def myxrange(stop):
    i = 0
    while i < stop:
        yield i
        i += 1
```

This function works by using the `yield` keyword, which pauses the function and remembers its current state. When the function is called again, it resumes from where it left off, starting from the next number in the sequence.

To use this function in a for loop, you can do the following:

```python
for i in myxrange(10):
    print(i)
```

This will output the numbers 0 through 9, just like `xrange(10)`.

## Conclusion

In summary, the `NameError: name 'xrange' is not defined` error occurs when you try to use the `xrange()` function in Python 3 or higher. This function has been removed in Python 3 because the `range()` function now behaves like `xrange()` did in Python 2. To generate sequences of numbers in Python 3, you can use the `range()` function or use generators to make the sequence more memory-efficient. Hopefully, this article has helped you understand why `xrange()` is not available in Python 3 and how to generate sequences of numbers in Python 3.