Factorial one-liner using reduce and mul for Python 2 and 3

---

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

---

$ foo bar | baz

Hi, readers,

A couple of days ago, I wrote this post for computing factorials using the reduce and operator.mul functions:

Factorial function using Python's reduce function

A bit later I realized that it can be made into a Python one-liner. Here is the one-liner - it works in both Python 2 and Python 3:

$ py -2 -c "from __future__ import print_function; from functools 
import reduce; from operator import mul; print(list(reduce(mul, 
range(1, fact_num + 1)) for fact_num in range(1, 11)))"
[1, 2, 6, 24, 120, 720, 5040, 40320, 362880, 3628800]

$ py -3 -c "from __future__ import print_function; from functools 
import reduce; from operator import mul; print(list(reduce(mul, 
range(1, fact_num + 1)) for fact_num in range(1, 11)))"
[1, 2, 6, 24, 120, 720, 5040, 40320, 362880, 3628800]

(I've split the commands above across multiple lines to avoid truncation while viewing, but if trying them out, enter each of the above commands on a single line.)

A small but interesting point is that one of the imports is not needed in Python 2, and the other is not needed in Python 3:

- importing print_function is not needed in Py 3, because in 3, print is a function, not a statement - but it is not an error to import it, for compatibility with Py 2 code - where it actually needs to be imported for compatibility with Py 3 code (for using print as a function), ha ha.

- importing reduce is not needed in Py 2, because in 2, reduce is both a built-in and also available in the functools module - and hence it is not an error to import it.

Because of the above two points, the same one-liner works in both Py 2 and Py 3.

Can you think of a similar Python one-liner that gives the same output as the above (and for both Py 2 and 3), but can work without one of the imports above (but by removing the same import for both Py 2 and 3)? If so, type it in a comment on the post.

py is The Python launcher for Windows.

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.

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

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

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.

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

---