## Tuesday, January 22, 2019

### 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

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.

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