Vasudev Ram: Factorial function using Python's reduce function

---

- By Vasudev Ram - Online Python training / SQL training / Linux training

---

[This is a beginner-level Python post. I label such posts as "python-beginners" in the Blogger labels at the bottom of the post. You can get a sub-feed of all such posts for any label using the label (case-sensitive) in a URL of the form:

http://bit.ly/2FEpOiG where label_name is to be replaced by an actual label,

such as in:

jugad2.blogspot.com/search/label/python-beginners

and

jugad2.blogspot.com/search/label/python
]

Hi, readers,

The factorial function (Wikipedia article) is often implemented in programming languages as either an iterative or a recursive function. Both are fairly simple to implement.

For the iterative version, to find the value of n factorial (written n! in mathematics), you set a variable called, say, product, equal to 1, then multiply it in a loop by each value of a variable i that ranges from 1 to n.

For the recursive version, you define the base case as 0! = 1, and then for all higher values of n factorial, you compute them recursively as the product of n with (n - 1) factorial.

[ Wikipedia article about Iteration. ]

[ Wikipedia article about Recursion in computer_science. ]

Here is another way of doing it, which is also iterative, but uses no explicit loop; instead it uses Python's built-in reduce() function, which is part of the functional programming paradigm or style:

In [179]: for fact_num in range(1, 11):
     ...:     print reduce(mul, range(1, fact_num + 1))
     ...:
1
2
6
24
120
720
5040
40320
362880
3628800

The above snippet (run in IPython - command-line version), loops over the values 1 to 10, and computes the factorial of each of those values, using reduce with operator.mul (which is a functional version of the multiplication operator). In more detail: the function call range(1, 11) returns a list with the values 1 to 10, and the for statement iterates over those values, passing each to the expression involving reduce and mul, which together compute each value's factorial, using the iterable returned by the second range call, which produces all the numbers that have to be multiplied together to get the factorial of fact_num.

The Python docstring for reduce:

reduce.__doc__: reduce(function, sequence[, initial]) -> value

Apply a function of two arguments cumulatively to the items of a sequence,
from left to right, so as to reduce the sequence to a single value.
For example, reduce(lambda x, y: x+y, [1, 2, 3, 4, 5]) calculates
((((1+2)+3)+4)+5).  If initial is present, it is placed before the items
of the sequence in the calculation, and serves as a default when the
sequence is empty.

Did you know that there are many different kinds of factorials? To learn more, check out this post:

Permutation facts

- Enjoy.

---

- Vasudev Ram - Online Python training and consulting

---

I conduct online courses on Python programming, Unix / Linux commands and shell scripting and SQL programming and database design, with course material and personal coaching sessions.

The course details and testimonials are here.

Contact me for details of course content, terms and schedule.

Try FreshBooks: Create and send professional looking invoices in less than 30 seconds.

Getting a new web site or blog, and want to help preserve the environment at the same time? Check out GreenGeeks.com web hosting.

Learning Linux? Hit the ground running with my vi quickstart tutorial. I wrote it at the request of two Windows system administrator friends who were given additional charge of some Unix systems. They later told me that it helped them to quickly start using vi to edit text files on Unix. Of course, vi/vim is one of the most ubiquitous text editors around, and works on most other common operating systems and on some uncommon ones too, so the knowledge of how to use it will carry over to those systems too.

Check out WP Engine, powerful WordPress hosting.

Sell More Digital Products With SendOwl.

Creating online products for sale? Check out ConvertKit, email marketing for online creators.

Teachable: feature-packed course creation platform, with unlimited video, courses and students.

Posts about: Python * DLang * xtopdf

My ActiveState Code recipes

Follow me on:

• My blog jugad2
• Gumroad
• LinkedIn
• Twitter

---

Vasudev Ram

from Planet Python
via read more