Python Number Conversion Chart | Hacker News Reader

Python Number Conversion Chart

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75 pointssnakile12 comments

It should be noted that data.encode('hex') and data.decode('hex') would not work in Python 3.x:

http://stackoverflow.com/q/12917278/23643

And for people who want to convert user entered numbers, like "3.2 million", into strings, I wrote a package especially for that: https://github.com/naftaliharris/numutil

    >>> from numutil import str2num, num2str
    >>> str2num('1.3 million')
    1300000
    >>> str2num('three and a half')
    Fraction(7, 2)
    >>> str2num('123,456.789')
    123456.789
    >>> num2str(1234567, style='newspaper')
    '1.23 million'
    >>> num2str(1234567, style='words')
    'one million, two hundred thirty four thousand, five hundred sixty seven'

Really useful, thanks for making this!

How is the "three and a half" part implemented? Is that just a set of regexes looking for a couple of common patterns? For example, can it parse something like "three and three thirds"?

Sure, I'm glad you like it! :)

str2num parses words by iterating through them once and keeping state about the result so far and what I call the "magnitude". So, for example, when you feed it "three and three thirds", it initializes magnitude and result to zero, chomps the first "three", and then sets magnitude = 3.

If the next word were "million", then it would know that magnitude refers to million, and so it would multiply 3 by 1 million. But the next word is "and", which flushes the magnitude to result, (ie, result += magnitude), and resets the magnitude to zero.

The next word is "three", which, as before, sets magnitude to three. Then the next word is "thirds", so you know that magnitude refers to "thirds", and so you multiply the magnitude by Fraction(1, 3) and add it to result.

  >>> str2num("three and three thirds")
  Fraction(4, 1)

The source for this is here: https://github.com/naftaliharris/numutil/blob/master/numutil...

of all the languages, python probably needs this the least. it's been my main language for 8 years, and once I initially learned the functions, I never needed to be reminded.

I think this kind of reference is useful just to remember what can be done "out of the box" with the language, especially for polyglot developers.

I've definitely written my own Python hex string -> binary data conversion function, before I knew some of these tricks. If you spend part of your time working in JavaScript or PHP, it's easy to forget that you don't have to reinvent the wheel with Python.

Direct link https://gist.github.com/Nurdok/4096182

'oct' should also be added:

    >>> oct(45)
    '055'

One caveat: Python doesn't assume the leading '0' indicates that the number is octal, so you must specify radix 8:

    >>> int('055', 8)
    45

Wouldn't it be better to comment on the direct link, where the author is more likely to see it?

Valid point, comment submitted. I assumed the author submitted this to HN in the first place

I would rather call that cause to celebrate than a caveat. The design of octal literals in C is ridiculous.

In fact you almost can't write a program without using them inadvertently. :)

Ruby translation: https://gist.github.com/havenwood/5426260

Partial Scala translation: https://gist.github.com/chris-martin/5426294

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