Python has two handy functions for creating lists, or a range of integers that assist in making
These functions are
range. But you probably already guessed that! 🙂
The Difference Between xrange and range in Python
Before we get started, let’s talk about what makes
For the most part,
range are the exact same in terms of functionality. They both provide a way to generate a list of integers for you to use, however you please. The only difference is that
range returns a Python
list object and
xrange returns an
What does that mean? Good question! It means that
xrange doesn’t actually generate a static list at run-time like
range does. It creates the values as you need them with a special technique called yielding. This technique is used with a type of object known as generators. If you want to read more in depth about generators and the yield keyword, be sure to checkout the article Python generators and the yield keyword.
Okay, now what does that mean? Another good question. That means that if you have a really gigantic range you’d like to generate a list for, say one billion,
xrange is the function to use. This is especially true if you have a really memory sensitive system such as a cell phone that you are working with, as
range will use as much memory as it can to create your array of integers, which can result in a
MemoryError and crash your program. It’s a memory hungry beast.
That being said, if you’d like to iterate over the list multiple times, it’s probably better to use
range. This is because
xrange has to generate an integer object every time you access an index, whereas
range is a static list and the integers are already “there” to use.
Alright, now on to the good stuff.
How to Use Python’s range and xrange
So how do we use
xrange? Here is the simplest example:
>>> for i in xrange(10): ... print(i) ... 0 1 2 3 4 5 6 7 8 9
Great! Simple enough. Note that you could also use
range in place of
xrange here, but I personally like
xrange better. Maybe it’s that sexy “x” in the front. 🙂
Alright, explanation time. The functions
range take in three arguments in total, however two of them are optional. The arguments are “start”, “stop” and “step”. “start” is what integer you’d like to start your list with, “stop” is what integer you’d like your list to stop at, and “step” is what your list elements will increment by.
Python’s xrange and range with Odd Numbers
Say we wanted only odd numbers. Here’s what we could do:
>>> for i in xrange(1, 10, 2): ... print(i) ... 1 3 5 7 9
We told Python that we would like the first element to be one, the last element to be one less than ten, and that we’d like each element to go up by two. Really simple stuff.
Python’s xrange and range with Negative Numbers
Alright, so what about if we want a negative list?
Simple. Here’s an example:
>>> for i in xrange(-1, -10, -1): ... print(i) ... -1 -2 -3 -4 -5 -6 -7 -8 -9
That’s it! All we have to do is change the “start”, “stop” and “step” to negative numbers. Awesome. Please note that you must do it this way for negative lists. Trying to use
xrange(-10) will not work because
range use a default “step” of one.
Another Python xrange and range Example
Here’s one more example of even numbers between 100 and 120:
>>> for i in xrange(100, 120, 2): ... print(i) ... 100 102 104 106 108 110 112 114 116 118
And that’s pretty much it for
range. If you would like a more technical explanation of what these two functions do, please consult the Python docs for xrange and range.
Note that if “start” is larger than “stop”, the list returned will be empty. Also, if “step” is larger that “stop” minus “start”, then “stop” will be raised to the value of “step” and the list will contain “start” as its only element.
Here’s a clearer picture:
>>> for i in xrange(70, 60): ... print(i) ... # Nothing is printed >>> for i in xrange(10, 60, 70): ... print(i) ... 10
Deprecation of Python’s xrange
One more thing to add. In Python 3.x, the
xrange function does not exist anymore. The
range function now does what
xrange does in Python 2.x, so to keep your code portable, you might want to stick to using
range instead. Of course, you could always use the 2to3 tool that Python provides in order to convert your code, but that introduces more complexity.
The reason why
xrange was removed was because it is basically always better to use it, and the performance effects are negligible. So Python 3.x’s
range function is
xrange from Python 2.x.
You can find the PEP document here for reasoning why it was removed.
Over and out, soldier. Over and out.