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What is considered an "advanced" topic in Python?

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  What is considered an "advanced" topic in Python? Mike Driscoll <kyosohma@gmail.com> - 2015-05-29 09:01 -0700
    Re: What is considered an "advanced" topic in Python? Joel Goldstick <joel.goldstick@gmail.com> - 2015-05-29 12:08 -0400
      Re: What is considered an "advanced" topic in Python? Mike Driscoll <kyosohma@gmail.com> - 2015-05-29 09:55 -0700
    Re: What is considered an "advanced" topic in Python? Chris Angelico <rosuav@gmail.com> - 2015-05-30 02:09 +1000
      Re: What is considered an "advanced" topic in Python? Mike Driscoll <kyosohma@gmail.com> - 2015-05-29 09:57 -0700
        Re: What is considered an "advanced" topic in Python? Chris Angelico <rosuav@gmail.com> - 2015-05-30 03:08 +1000
        Re: What is considered an "advanced" topic in Python? random832@fastmail.us - 2015-05-31 23:18 -0400
        Re: What is considered an "advanced" topic in Python? Chris Angelico <rosuav@gmail.com> - 2015-06-01 13:43 +1000
        Re: What is considered an "advanced" topic in Python? Laura Creighton <lac@openend.se> - 2015-06-01 09:58 +0200
          Re: What is considered an "advanced" topic in Python? Marko Rauhamaa <marko@pacujo.net> - 2015-06-01 12:36 +0300
            Zero [was Re: What is considered an "advanced" topic in Python?] Steven D'Aprano <steve@pearwood.info> - 2015-06-01 22:07 +1000
              Re: Zero [was Re: What is considered an "advanced" topic in Python?] Laura Creighton <lac@openend.se> - 2015-06-01 14:52 +0200
              Re: Zero [was Re: What is considered an "advanced" topic in Python?] Dave Farrance <DaveFarrance@OMiTTHiSyahooANDTHiS.co.uk> - 2015-06-01 13:56 +0100
                Re: Zero [was Re: What is considered an "advanced" topic in Python?] Skip Montanaro <skip.montanaro@gmail.com> - 2015-06-01 08:14 -0500
                  Re: Zero [was Re: What is considered an "advanced" topic in Python?] Dave Farrance <df@see.replyto.invalid> - 2015-06-01 15:39 +0100
                Re: Zero [was Re: What is considered an "advanced" topic in Python?] Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-06-01 18:35 +0100
                Re: Zero [was Re: What is considered an "advanced" topic in Python?] Terry Reedy <tjreedy@udel.edu> - 2015-06-01 17:32 -0400
              Re: Zero [was Re: What is considered an "advanced" topic in Python?] Marko Rauhamaa <marko@pacujo.net> - 2015-06-01 16:18 +0300
                Re: Zero [was Re: What is considered an "advanced" topic in Python?] random832@fastmail.us - 2015-06-01 09:32 -0400
          Re: What is considered an "advanced" topic in Python? Dave Farrance <DaveFarrance@OMiTTHiSyahooANDTHiS.co.uk> - 2015-06-01 11:44 +0100
            Re: What is considered an "advanced" topic in Python? Marko Rauhamaa <marko@pacujo.net> - 2015-06-01 13:54 +0300
          Re: What is considered an "advanced" topic in Python? Rustom Mody <rustompmody@gmail.com> - 2015-06-01 22:33 -0700
        Re: What is considered an "advanced" topic in Python? Chris Angelico <rosuav@gmail.com> - 2015-06-01 19:45 +1000
        Re: What is considered an "advanced" topic in Python? Laura Creighton <lac@openend.se> - 2015-06-01 12:28 +0200
          Re: What is considered an "advanced" topic in Python? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-06-01 14:22 +0100
        Re: What is considered an "advanced" topic in Python? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-06-01 11:34 +0100
        Re: What is considered an "advanced" topic in Python? Chris Angelico <rosuav@gmail.com> - 2015-06-01 20:36 +1000
        Re: What is considered an "advanced" topic in Python? Laura Creighton <lac@openend.se> - 2015-06-01 13:00 +0200
        Re: What is considered an "advanced" topic in Python? Laura Creighton <lac@openend.se> - 2015-06-01 13:24 +0200
          Re: What is considered an "advanced" topic in Python? Marko Rauhamaa <marko@pacujo.net> - 2015-06-01 14:57 +0300
            Re: What is considered an "advanced" topic in Python? BartC <bc@freeuk.com> - 2015-06-01 13:27 +0100
            Re: What is considered an "advanced" topic in Python? MRAB <python@mrabarnett.plus.com> - 2015-06-01 13:27 +0100
            Re: What is considered an "advanced" topic in Python? Laura Creighton <lac@openend.se> - 2015-06-01 17:07 +0200
              Re: What is considered an "advanced" topic in Python? alister <alister.nospam.ware@ntlworld.com> - 2015-06-01 15:26 +0000
                Re: What is considered an "advanced" topic in Python? Laura Creighton <lac@openend.se> - 2015-06-01 17:51 +0200
                Re: What is considered an "advanced" topic in Python? MRAB <python@mrabarnett.plus.com> - 2015-06-01 18:06 +0100
                  Re: What is considered an "advanced" topic in Python? Marko Rauhamaa <marko@pacujo.net> - 2015-06-01 20:14 +0300
              Re: What is considered an "advanced" topic in Python? BartC <bc@freeuk.com> - 2015-06-01 16:42 +0100
                Re: What is considered an "advanced" topic in Python? Grant Edwards <invalid@invalid.invalid> - 2015-06-01 17:02 +0000
                  Re: What is considered an "advanced" topic in Python? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-06-01 18:45 +0100
                    Re: What is considered an "advanced" topic in Python? Grant Edwards <invalid@invalid.invalid> - 2015-06-01 18:23 +0000
          Re: What is considered an "advanced" topic in Python? BartC <bc@freeuk.com> - 2015-06-01 13:24 +0100
        Re: What is considered an "advanced" topic in Python? Chris Angelico <rosuav@gmail.com> - 2015-06-01 23:52 +1000
          Re: What is considered an "advanced" topic in Python? BartC <bc@freeuk.com> - 2015-06-01 16:17 +0100
            Re: What is considered an "advanced" topic in Python? Chris Angelico <rosuav@gmail.com> - 2015-06-02 02:10 +1000
              Re: What is considered an "advanced" topic in Python? Rustom Mody <rustompmody@gmail.com> - 2015-06-01 21:46 -0700
    Re: What is considered an "advanced" topic in Python? Skip Montanaro <skip.montanaro@gmail.com> - 2015-05-29 11:39 -0500
      Re: What is considered an "advanced" topic in Python? Mike Driscoll <kyosohma@gmail.com> - 2015-05-29 09:58 -0700
    Re: What is considered an "advanced" topic in Python? Chris Angelico <rosuav@gmail.com> - 2015-05-30 02:50 +1000
    Re: What is considered an "advanced" topic in Python? Todd <toddrjen@gmail.com> - 2015-05-29 19:02 +0200
    Re: What is considered an "advanced" topic in Python? sohcahtoa82@gmail.com - 2015-05-29 10:03 -0700
      Re: What is considered an "advanced" topic in Python? Ethan Furman <ethan@stoneleaf.us> - 2015-05-29 10:17 -0700
        Re: What is considered an "advanced" topic in Python? sohcahtoa82@gmail.com - 2015-05-29 14:06 -0700
          Re: What is considered an "advanced" topic in Python? Jason Swails <jason.swails@gmail.com> - 2015-05-29 17:28 -0400
          Re: What is considered an "advanced" topic in Python? Ethan Furman <ethan@stoneleaf.us> - 2015-05-29 14:39 -0700
          Re: What is considered an "advanced" topic in Python? Ethan Furman <ethan@stoneleaf.us> - 2015-05-29 14:44 -0700
      Re: What is considered an "advanced" topic in Python? Marko Rauhamaa <marko@pacujo.net> - 2015-05-29 20:24 +0300
    Re: What is considered an "advanced" topic in Python? Todd <toddrjen@gmail.com> - 2015-05-29 19:03 +0200
    Re: What is considered an "advanced" topic in Python? Steven D'Aprano <steve@pearwood.info> - 2015-05-30 03:55 +1000
      Re: What is considered an "advanced" topic in Python? Mike Driscoll <kyosohma@gmail.com> - 2015-05-29 13:38 -0700
    Re: What is considered an "advanced" topic in Python? Sturla Molden <sturla.molden@gmail.com> - 2015-05-30 12:15 +0000
    Re: What is considered an "advanced" topic in Python? jonathon <jonathon.blake@gmail.com> - 2015-05-30 19:32 +0000
    Re: What is considered an "advanced" topic in Python? Chris Angelico <rosuav@gmail.com> - 2015-05-31 08:24 +1000
    Re: What is considered an "advanced" topic in Python? "C.D. Reimer" <chris@cdreimer.com> - 2015-05-30 18:28 -0700
    Re: What is considered an "advanced" topic in Python? Rustom Mody <rustompmody@gmail.com> - 2015-05-30 20:30 -0700
      Re: What is considered an "advanced" topic in Python? Chris Angelico <rosuav@gmail.com> - 2015-05-31 14:25 +1000
        Re: What is considered an "advanced" topic in Python? Rustom Mody <rustompmody@gmail.com> - 2015-05-30 21:46 -0700
          Re: What is considered an "advanced" topic in Python? Chris Angelico <rosuav@gmail.com> - 2015-05-31 14:58 +1000
            Re: What is considered an "advanced" topic in Python? Rustom Mody <rustompmody@gmail.com> - 2015-05-30 22:18 -0700
    Re: What is considered an "advanced" topic in Python? Gene Heskett <gheskett@wdtv.com> - 2015-06-01 09:49 -0400
    Re: What is considered an "advanced" topic in Python? Denis McMahon <denismfmcmahon@gmail.com> - 2015-06-01 15:30 +0000
    Re: What is considered an "advanced" topic in Python? Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2015-06-01 20:33 -0400
    Re: What is considered an "advanced" topic in Python? Gene Heskett <gheskett@wdtv.com> - 2015-06-01 23:30 -0400

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#91468 — What is considered an "advanced" topic in Python?

Hi,

I've been asked on several occasions to write about intermediate or advanced topics in Python and I was wondering what the community considers to be "intermediate" or "advanced". I realize we're all growing in our abilities with the language, so this is going to be very subjective, but I am still curious what my fellow Python developers think about this topic.

Thanks,
Mike

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#91469

Maybe itertools or generators

On Fri, May 29, 2015 at 12:01 PM, Mike Driscoll <kyosohma@gmail.com> wrote:
> Hi,
>
> I've been asked on several occasions to write about intermediate or advanced topics in Python and I was wondering what the community considers to be "intermediate" or "advanced". I realize we're all growing in our abilities with the language, so this is going to be very subjective, but I am still curious what my fellow Python developers think about this topic.
>
> Thanks,
> Mike
> --
> https://mail.python.org/mailman/listinfo/python-list



-- 
Joel Goldstick
http://joelgoldstick.com

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#91478

On Friday, May 29, 2015 at 11:08:19 AM UTC-5, Joel Goldstick wrote:
> Maybe itertools or generators
> 

Yeah, I was thinking along those lines. I was also thinking about some of the cool stuff in the collections and contextlib modules.

Mike

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#91470

On Sat, May 30, 2015 at 2:01 AM, Mike Driscoll <kyosohma@gmail.com> wrote:
> I've been asked on several occasions to write about intermediate or advanced topics in Python and I was wondering what the community considers to be "intermediate" or "advanced". I realize we're all growing in our abilities with the language, so this is going to be very subjective, but I am still curious what my fellow Python developers think about this topic.
>

Good fun! A few ideas:

How to write decorators, particularly those that take parameters.

The differences between the various number types (int, float, complex,
Fraction, Decimal) and when you'd want each one.

(CPython-specific) The dis.dis() function and what it can tell you
about how Python operates

These are all topics that have come up with my students; they're
advanced enough to be outside the scope of the course itself (the
course _uses_ decorators, but doesn't explain how to actually build
them), but not beyond the grasp of someone who's mastered Python's
fundamentals.

ChrisA

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#91479

> 
> Good fun! A few ideas:
> 
> How to write decorators, particularly those that take parameters.


Yes, this one always seems to trip people up.


> 
> The differences between the various number types (int, float, complex,
> Fraction, Decimal) and when you'd want each one.

I hadn't considered this one


> 
> (CPython-specific) The dis.dis() function and what it can tell you
> about how Python operates

I remember seeing on PyMOTW - http://pymotw.com/2/dis/  I agree that it's a module most programmers don't know about.


> 
> These are all topics that have come up with my students; they're
> advanced enough to be outside the scope of the course itself (the
> course _uses_ decorators, but doesn't explain how to actually build
> them), but not beyond the grasp of someone who's mastered Python's
> fundamentals.
> 
> ChrisA

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#91485

On Sat, May 30, 2015 at 2:57 AM, Mike Driscoll <kyosohma@gmail.com> wrote:
>>
>> Good fun! A few ideas:
>>
>> How to write decorators, particularly those that take parameters.
>
> Yes, this one always seems to trip people up.

It's like a Sherlock Holmes pronouncement. When you see something like
Flask's app.route(), or functools.wraps(), it's pure magic and
completely incomprehensible. But break it down into little pieces (a
function that takes a function and returns a function, then decorator
syntax, then closures and the ability to call the original, and
finally a decorator factory function, which is what a parameterized
decorator is), and it becomes elementary.

>> The differences between the various number types (int, float, complex,
>> Fraction, Decimal) and when you'd want each one.
>
> I hadn't considered this one

It's not often an actual *problem* - I've never seen anyone pick the
wrong data type and mess up their code, not in Python - but it's a
great way to explore some of the differences between real numbers and
what computers work with. Also, I like talking about Fraction and
Decimal for the simple reason that they're unobvious; you can poke
around with Python and discover int and float, and if ever you need
imaginary/complex numbers, you'll quickly come across complex, but you
might use Python for years and not realize that decimal.Decimal even
exists - nor when you'd want it.

ChrisA

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#91610

On Fri, May 29, 2015, at 13:08, Chris Angelico wrote:
> Also, I like talking about Fraction and
> Decimal for the simple reason that they're unobvious; you can poke
> around with Python and discover int and float, and if ever you need
> imaginary/complex numbers, you'll quickly come across complex, but you
> might use Python for years and not realize that decimal.Decimal even
> exists - nor when you'd want it.

Well, isn't that just a byproduct of what problem space you work in? If
someone _does_ know they need a rational or decimal type (e.g. someone
working with money who's clueful enough to know floats won't do),
they'll find these types relatively quickly from a google search -
there's no glut of third-party implementations, and neither is so
obscure nor easily written from scratch that people wouldn't search for
an existing implementation.

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#91617

On Mon, Jun 1, 2015 at 1:18 PM,  <random832@fastmail.us> wrote:
> On Fri, May 29, 2015, at 13:08, Chris Angelico wrote:
>> Also, I like talking about Fraction and
>> Decimal for the simple reason that they're unobvious; you can poke
>> around with Python and discover int and float, and if ever you need
>> imaginary/complex numbers, you'll quickly come across complex, but you
>> might use Python for years and not realize that decimal.Decimal even
>> exists - nor when you'd want it.
>
> Well, isn't that just a byproduct of what problem space you work in? If
> someone _does_ know they need a rational or decimal type (e.g. someone
> working with money who's clueful enough to know floats won't do),
> they'll find these types relatively quickly from a google search -
> there's no glut of third-party implementations, and neither is so
> obscure nor easily written from scratch that people wouldn't search for
> an existing implementation.

Yes, but how many people actually know they need a rational type? Just
now there's a thread on python-ideas that was based around the
expectation that a float could do that, which it can't; the OP just
naturally assumed that float was the data type he should be using.

ChrisA

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#91631

If you are giving a talk about Decimal -- and trying to stamp out the
inappropriate use of floats you have to first inform people that
what they learned as 'decimals' as children was not floating point,
despite the fact that we write them the same way.

If I ever get the time machine, I am going back in time and demand that
floating point numbers be expressed as 12345:678 instead of 12345.678
because it would save so much trouble.  Never has the adage 'It's not
what you don't know, that bites you.  It's what you know that ain't so.'
been more apt.

I have done much better in speaking about this topic to a bunch of
incredulous people if you next explain that scientists really don't
care about accuracy in their calculations.  (This will surprise them).
Most scentific calculations have some real world measurement in them,
and for most real world measurements, if you are getting even 5 digits
of precision, you are doing really, really, well.  This means that
scientists are going to be throwing away all the extra digits they get
out a a floating point representation, so they don't have to care how
accurate they are.  As long as their results are good in the first 5,
it won't matter.  (Depending on time constraints, a review of
significant figures -- what they are and what they mean is good here.)

It is really hard to get the concept of Decimal across to people who
already have that concept in their mind, but think it is called Float.
You have to first teach them that they don't know anything about Float
and get them to reboot their brains before you can install this new
knowledge.  Otherwise their brains will just overwrite your new knowledge
with 'ah, just use a Float' as soon as you stop speaking.  Same day,
even.

Laura

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#91639

Laura Creighton <lac@openend.se>:

> It is really hard to get the concept of Decimal across to people who
> already have that concept in their mind, but think it is called Float.

I can't remember running into this frustration.

However, I *constantly* run into engineers who don't understand what
zero means.


Marko

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#91660 — Zero [was Re: What is considered an "advanced" topic in Python?]

On Mon, 1 Jun 2015 07:36 pm, Marko Rauhamaa wrote:

> However, I constantly run into engineers who don't understand what
> zero means.

Okay, I'll bite.

What does zero mean, and how do engineers misunderstand it?



-- 
Steven

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#91665 — Re: Zero [was Re: What is considered an "advanced" topic in Python?]

In a message of Mon, 01 Jun 2015 22:07:41 +1000, "Steven D'Aprano" writes:
>On Mon, 1 Jun 2015 07:36 pm, Marko Rauhamaa wrote:
>
>> However, I constantly run into engineers who don't understand what
>> zero means.
>
>Okay, I'll bite.
>
>What does zero mean, and how do engineers misunderstand it?
>
>
>
>-- 
>Steven

I assume he meant 0 padding for fast fourier transforms, but I could
be wrong about that, too.

Laura

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#91666 — Re: Zero [was Re: What is considered an "advanced" topic in Python?]

Steven D'Aprano <steve@pearwood.info> wrote:

>On Mon, 1 Jun 2015 07:36 pm, Marko Rauhamaa wrote:
>
>> However, I constantly run into engineers who don't understand what
>> zero means.
>
>Okay, I'll bite.
>
>What does zero mean, and how do engineers misunderstand it?

There are two hard things in computer science: cache invalidation,
naming things, and off-by-one errors.

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#91667 — Re: Zero [was Re: What is considered an "advanced" topic in Python?]

[Multipart message — attachments visible in raw view] — view raw

On Mon, Jun 1, 2015 at 7:56 AM, Dave Farrance <
DaveFarrance@omitthisyahooandthis.co.uk> wrote:
> There are two hard things in computer science: cache invalidation, naming
things, and off-by-one errors.

So it's 1 that engineers really don't understand? Just add 1 and you get
the correct number of hard things. <wink>

Skip

P.S., Dave, your "omitthis" and "andthis" kind of sucks for the rest of us.
And I just invalidated your attempts at
obscurity by replying to your correct email address. I suggest you just
omit that stuff going forward. Unfortunately,
I now I have a crap address in my Gmail contacts I have to hunt down and
remove. Maybe you should just install
a decent spam filter <http://www.spambayes.org/> or switch to Gmail, which
has a functioning spam filter (unlike Yahoo...)

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#91676 — Re: Zero [was Re: What is considered an "advanced" topic in Python?]

Skip Montanaro <skip.montanaro@gmail.com> wrote:

>P.S., Dave, your "omitthis" and "andthis" kind of sucks for the rest of us.
>And I just invalidated your attempts at
>obscurity by replying to your correct email address. I suggest you just
>omit that stuff going forward. Unfortunately,
>I now I have a crap address in my Gmail contacts I have to hunt down and
>remove. Maybe you should just install
>a decent spam filter <http://www.spambayes.org/> or switch to Gmail, which
>has a functioning spam filter (unlike Yahoo...)

I've had that as my Usenet address since 2000 when Usenet was the prime
spam harvesting source and the spammers were actively using
anti-address-munging techniques.  That's no longer so much of a problem,
given Usenet's obscurity for today's average Internet user, but I'm
still wary of posting email addresses directly to Usenet.  I've changed
the "from" address to end with ".invalid" which is the RFC way, and
should be stopped at the Email client, if that helps.

Since this is "comp.lang.python", I'm assuming that it should be treated
primarily as a Usenet group in which you'd normally reply to the group
-- rather than by personal email as you might do if this was primarily a
Listserv group.  I dunno what the group thinks about that.  A quick
header check tells me that the posters here are split about 50/50
between posting via Usenet or the list server.
  

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#91701 — Re: Zero [was Re: What is considered an "advanced" topic in Python?]

On 01/06/2015 14:14, Skip Montanaro wrote:
>
> Maybe you should just install
> a decent spam filter <http://www.spambayes.org/> or switch to Gmail,
> which has a functioning spam filter (unlike Yahoo...)
>

Okay I'll bite, what's wrong with the Yahoo spam filter?

-- 
My fellow Pythonistas, ask not what our language can do for you, ask
what you can do for our language.

Mark Lawrence

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#91717 — Re: Zero [was Re: What is considered an "advanced" topic in Python?]

On 6/1/2015 9:14 AM, Skip Montanaro wrote:

> remove. Maybe you should just install
> a decent spam filter <http://www.spambayes.org/> or switch to Gmail,
> which has a functioning spam filter (unlike Yahoo...)

For me, Yahoo's spam filter is comparable to Gmail's.  (My udel account 
is actually handled by gmail.)  Either spam has decreased recently or 
both have gotten better at putting fewer things in the junk box for 
checking and tossing away more things.

-- 
Terry Jan Reedy

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#91668 — Re: Zero [was Re: What is considered an "advanced" topic in Python?]

Steven D'Aprano <steve@pearwood.info>:

> What does zero mean, and how do engineers misunderstand it?

Off the top of my head:

 * Code that does:

      if elements:
          for element in elements:
              ...

   instead of:

      for elements in elements:
          ...

 * C++ insists that all objects have nonzero sizes. This program:

   ====================================================================
   #include <stdio.h>
   struct S {};
   int main()
   {
       printf("%zd\n", sizeof(struct S));
       return 0;
   }
   ====================================================================

   prints out 1 when compiled with c++ but 0 when compiled with cc.

 * In C, it used to be illegal to define a struct without a dummy field
   or a zero-length array. At one point, that created irritating trouble
   for compilers that generated C.

 * malloc(0) is allowed to return NULL as a successful return value
   inviting application programming errors. Calling free(NULL) didn't
   use to be guaranteed to work.

 * Numerous shell commands assign special meaning to zero arguments.
   For example:

      $ ls a b c
      a b c
      $ ls a b
      a b
      $ ls a
      a
      $ ls
      a b c d e f g

      $ ln -s a b c
      # creates two links under c, which must be a directory
      $ ln -s c
      # creates one link under .

 * Wild-card expansion always produces at least one result:

      for src in *.py; do
          # executed even in the absence of a .py file
      done

 * Python insists that a block contain at least one statement even
   though technically, it is not necessary for syntactic reasons. Not a
   biggie but can cause a minor annoyance when commenting out a line.

 * Numerous timer implementations take 0 to mean infinity. For example,
   in Java:

       public final void wait(long timeout)
                throws InterruptedException

       [...] If timeout is zero, however, then real time is not taken
       into consideration and the thread simply waits until notified.

       <URL: https://docs.oracle.com/javase/7/docs/api/java/lan
       g/Object.html#wait%28long%29>

   A nasty surprise for those who'd naively expect zero to mean zero,
   especially if zero is the result of downward rounding.


Marko

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#91671 — Re: Zero [was Re: What is considered an "advanced" topic in Python?]

On Mon, Jun 1, 2015, at 09:18, Marko Rauhamaa wrote:
>       if elements:
>           for element in elements:
>               ...
> 
>    instead of:
> 
>       for elements in elements:

TypeError: 'NoneType' object is not iterable

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#91652

Laura Creighton <lac@openend.se> wrote:

>If you are giving a talk about Decimal -- and trying to stamp out the
>inappropriate use of floats you have to first inform people that
>what they learned as 'decimals' as children was not floating point,
>despite the fact that we write them the same way. ...

To be fair, prior to electronic computers, they were essentially
synonymous.  It's a bit like finance experts chiding people for mixing
"cost" with "price".

>>> Decimal('0.3')
Decimal('0.3')
>>> Decimal(0.3)
Decimal('0.299999999999999988897769753748434595763683319091796875')

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