Python 3 semantics for integer division

As I refresh my skills in Python 2 to Python 3 semantics I discovered there is a difference in the division operator (i.e. /).

When using integers in Python 2 the result (by default) is an integer. For example.

$ python2
Python 2.7.6 (default, Mar 22 2014, 22:59:56)
>>> 1/2
0
>>> 1/2.0
0.5

In Python 3 the result is a float.

$ python3
Python 3.4.0 (default, Apr 11 2014, 13:05:11)
>>> 1/2
0.5

It has been encouraged in the Porting Python 2 Code to Python 3 documentation to perform the following import.

$ python2
Python 2.7.6 (default, Mar 22 2014, 22:59:56)
>>> from __future__ import division
>>> 1/2
0.5

I was also unaware of the floor operator (i.e. //) as specified in PEP 238 .

$ python2
Python 2.7.6 (default, Mar 22 2014, 22:59:56)
>>> from __future__ import division
>>> 1//2
0
>>> 1/2
0.5

I uncovered this by playing with algorithms between versions. This Newton Method for the Square Root was something I was unaware of, and this example failed when using Python 2.

My improved version on the referenced example without an import.

def squareroot(number, precision = 5):
  root = number/2.0
  for i in range(20):
    nroot = (1/2.0)*(root + (number / root))
    #print i, nroot
    if (root - nroot < 1.0/10**precision):
      break
    root = nroot
  return round(nroot, precision)
>>> squareroot(10)
3.16228
>>> squareroot(10,1)
3.2
>>> squareroot(10,2)
3.16
>>> squareroot(10,5)
3.16228
>>> squareroot(10,10)
3.1622776602
Tagged with: Python

Related Posts

Migrating MySQL latin1 to utf8 – Character Set Options

Continuing on from preparation in our MySQL latin1 to utf8 migration let us first understand where MySQL uses character sets. MySQL defines the character set at 4 different levels for the structure of data.

Read more

Migrating MySQL latin1 to utf8 – Preparation

This article is Part 1 of a series of articles regarding MySQL character set conversion. Be sure to also check out character set options and the process for more information.

Read more

MySQL and Heatwave Summit Presentation

Last week I had the opportunity to speak at the MySQL and Heatwave Summit in San Francisco. I discussed the impact of the new MySQL 8.0 default caching_sha2_password authentication, replacing the mysql_native_password authentication that was the default for approximately 20 of the 30 years that MySQL has existed.

Read more