Allow to use units with numbers in iPython, e.g. "1n"=1e-9 or "1G"=1e9

euext.py

# -*- coding: utf-8 -*-
"""
IPython extension for engineering units
See README.txt for usage examples.

Author: Juergen Hasch <python@elbonia.de>
Parts taken from the physics.py extension by Georg Brandl <georg@python.org>
This file has been placed in the public domain.

Allows units to be specified like
  1n
or
  1 n
or
  1e3p
  
"""

import re
import sys
from math import pi

number = r'(-?[\d0-9.-]+)'
unit = r'([a-df-zA-Z1°µ][a-df-zA-Z0-9°µ/^-]*)'
match =    number +  r'\s*' + unit 

_prefixes = {
    'Y':  1.e24 , 'Z':  1.e21, 'E':  1.e18, 'P':  1.e15, 'T':  1.e12,
    'G':  1.e9,  'M':  1.e6,  'k':  1.e3,  'h':  1.e2,  'da': 1.e1,
    'd':  1.e-1, 'c':  1.e-2, 'm':  1.e-3, 'mu': 1.e-6, 'u': 1.e-6, 'n':  1.e-9,
    'p':  1.e-12, 'f':  1.e-15, 'a': 1.e-18, 'z':  1.e-2,
    'y':  1.e-24,
}

def replace_inline(mo):
    """Replace unit by quantity
    """
    try:
         return mo.group(1) + "*" + str(_prefixes[mo.group(2)])
    except KeyError:
        return mo.group(2)

class QTransformer(object):
    """IPython command line transformer that recognizes and replaces unit
    expressions.
    """
    # XXX: inheriting from PrefilterTransformer as documented gives TypeErrors,
    # but apparently is not needed after all
    priority = 99
    enabled = True
    def transform(self, line, continue_prompt):
        line = re.sub(match,replace_inline, line)
        return line

q_transformer = QTransformer()

def load_ipython_extension(ip):
    ip.prefilter_manager.register_transformer(q_transformer)

    print 'Engineering Units extension activated.'

def unload_ipython_extension(ip):
    ip.prefilter_manager.unregister_transformer(q_transformer)