Python Facts

http://facts.learnpython.org/

by ronreiter • 15 years ago

228 104 15 years ago

facts.learnpython.org

mapleoin2• 15 years ago

It would be nice if all these "facts" could be downloadable under a CC license.

ronreiter9• 15 years ago

good idea. will do

ralph• 15 years ago

"View All" only give me the titles, I still need to look at each individually. It's a bit like a FAQ that doesn't put multiple Qs and As on the same page; a pain. Part of the benefit would be scrolling through at speed, no comments interspersed, learning quickly, skipping already-known at a glance. Could be N per page to handle when total number is large as long as N >= 20. I'm looking at View All thinking some look interesting but I haven't the time to click round it all.

veyron• 15 years ago

Is this approach (sending the commands to a backend) preferable to a javascript-based repl (using something like emscripten)?

ronreiter9• 15 years ago

yes, but it's jailed pretty good and it's not a lot of CPU power to execute, so it's OK.

RyanMcGreal2• 15 years ago

It allows `eval()` to run. Please see this:

http://diveintopython3.ep.io/advanced-iterators.html#eval

nanotone• 15 years ago

It looks like you're using GAE. Not having much experience with it, I'm wondering if GAE provides the CPU jailing, or did you have to write some voodoo yourself?

I ask because it's trivially easy to send a statement containing a single bytecode that takes a really long time to execute, at least in CPython:

>>> print 999 * 0 # => 0, so not a bandwidth issue

If I send this to your backend in a bunch of tabs (I didn't) could that be a DoS?

Also, are you thinking of putting the backend code on github?

EDIT: HN swallowed my exponentiation. That should read "print nine to the nine to the nine, times zero". Without the times zero, that's a huge number.

MostAwesomeDude2• 15 years ago

"There should be one -- and preferably only one -- obvious way to do it. If the implementation is easy to explain, it may be a good idea." AFAIK there is not a JavaScript version of Python which is fully compliant with the Python 2.6 specification.

ronreiter9• 15 years ago

I think he meant that it would be better if the Python interpreter would be implemented in Javascript. right?

cschmidt• 15 years ago

If whoever created this stops by, I got an error message on this snippet:

    import itertools
    name_generator = itertools.imap("name-{}".format,itertools.count())
    # to get the next name:
    new_name = next(name_generator)

ronreiter9• 15 years ago

thanks

rplnt• 15 years ago

http://facts.learnpython.org/2003 gives me error as well

zalew• 15 years ago

I came across another error

map(int, "10 20 30".split())

Output:

AgentConundrum• 15 years ago

What's the error you're getting? That code worked fine for me (2.7.2)

    >>> import itertools
    >>> name_generator = itertools.imap("name-{}".format,itertools.count())
    >>> new_name = next(name_generator)
    >>> new_name
    'name-0'
    >>> new_name = next(name_generator)
    >>> new_name
    'name-1'

koenigdavidmj• 15 years ago

In 2.6 or earlier replace the last line with:

  new_name = name_generator.next()

neq• 15 years ago

The python version available is 2.5.2 yet some of the tips use newer features and syntax. This is definitely a problem.

c4urself• 15 years ago

cool initative! seems like snippet numbers are random: 1 works but 2, 3, 4 don't. it would be nice to have categories or tags and a place to let others contribute snippets. i like the fact that the snippets are small and communicate one thing, otherwise it's comparable to the ActiveState website. It would be nice to make it downloadable in a pdf.

EDIT: Never mind I see there is an "Add" button.

pace10• 15 years ago

Can it be true that the Python coverage on HN is overproportional compared to its real world usage?

If I look around the world is full of Ruby and Rails. Sites, libs, meetups, developers, everything is on Ruby or Ruby on Rails. Python and Django devs are so damn rare in real world -- I just know two of 100.

Not that I don't like Python but I am really wondering why Python gets such a strong coverage on HN. Every second day there's some Python thing on HN. BTW with Clojure it's the same but Clojure is something new, so I understand the visibility there.

Please don't downvote -- it's nothing against Python, I just want to see if the Python base increased or something happend I've missed. Thanks

How can it be?

EDIT: Thanks to all for the replies. What's interesting about this thread: I got tons of downvotes (besides upvotes) for the first comment. So, I assume this Python vs Ruby discussion seems to be a very emotional topic. Thanks to the replies I have now a better understanding that Python is older and dominant in a many non-web environments. My impression is still that especially in web environments we have much more pace and development in Rails than Django (just compare what DHH put in 3.1, Coffee, Sass, etc. -- no flame war just a questions dear downvoters, don't freak out again)--Rails feels just more vibrant regarding web dev. But Rails is not Ruby ;-) It's just that I see all the Python stuff on HN -- which is slightly focussed on online/web/Internet -- and I really considered learning Python for web dev until I checked http://www.google.de/trends?q=python+django%2C+ruby+rails...

EDIT2: but there's a new rising star: http://www.google.de/trends?q=python+django%2C+ruby+rails%2C...

JanezStupar4• 15 years ago

Conversely I know 20 Python Django/Pyramid developers and one Rails developer.

pace10• 15 years ago

where r u located?

dagw• 15 years ago

Same here. I don't know any Ruby developers here in Sweden, but half the programmers I know use python.

shantanubala• 15 years ago

Python has a very large community, but it tends to be a lot less vocal (for better or worse) than the Ruby or Rails communities. Python is a widely used language (quite possibly much more popular than Ruby since Python is taught to undergraduates at MIT, Berkeley, and other "top tier" schools).

TylerE• 15 years ago

It's pretty much certain, given the widespread acceptance python has in scientific computing, an area where Ruby penetration is minimal-to-nonexistant.

jteo• 15 years ago

The plural of anecdote is not data.

halostatue• 15 years ago

I don't think so. I know mostly Ruby developers, but that's because I'm in the Ruby world. As far as I can tell, the Python community is somewhat larger—and there are certain communities where it will likely stay that way (e.g., scientific computing is a bit of a travesty in Ruby, but substantially better in Python).

Ruby makes me happier than Python does, but Python is widely used.

ippisl• 15 years ago

I did a quick job search in monster.co.uk and got:

ruby -160 jobs.

python - 356 jobs.

ronreiter9• 15 years ago

pwned

draegtun2• 15 years ago

Ditto and also got this for:

Perl - 363 jobs.

PHP - 769 jobs.

C++ - 814 jobs.

Java - 1,000+ jobs

C# - 1,000+ jobs

jiggy20112• 15 years ago

I'm always skeptical where people post stats from jobs websites.

I think allot of the advertised jobs are either duplicates or recruiters who just advertise there in order to harvest CVs, so it may be more a barometer of what is perceived to be popular rather than what actually is.

djb_hackernews• 15 years ago

Come to DC. It's all Python and no Ruby.

callahad• 15 years ago

As far as I can tell, Python has a much broader base than Ruby, at least in the english-speaking world, but is generally quieter about it. As a few examples:

Thanks to SciPy, NumPy, Sage, and so on, Python is extremely popular in scientific computing and academia in general, drawing hundreds each year to Enthought's Scientific Python conference.

Apple's iCal Server is written in Python with the aid of the Twisted async library, the same library used by LucasFilm for communications in its render farm, or Justin.tv's caching engine.

Google has found great success with Python: YouTube, for instance, is written in Python.

Thousands of undergraduates have their introduction to computer science each year taught in Python, even at MIT.

And let's not forget the sizable Django, Pyramid, and Plone web development communities, all of which seem to have surprisingly little overlap.

The thing is, Python's been around for a long time -- longer than Java -- and it's been useful for a similarly long time, especially in the same domains that Perl traditionally excelled at. Thus, its growth was bottom-up: Many sysadmins were eventually expected to simply know Python just as they were expected to know Shell and Perl, and thus being functionally proficient in Python wasn't really a defining characteristic.

In this way, Python's expansion has been more of a slow burn as it creeps into more and more corners of software development. Rails, by contrast, came coupled with a wonderful promoter in DHH, and brought scores of front-end talent and PHP refugees into the fold from day one. That audience seems to simply be more innately talented at vocalizing the cool things they're doing, and making sure they mention that they did it all "...with Ruby!"

So while I'd wager that the Python community is larger than the Ruby community, it certainly seems less concentrated, and less vocal about it.

To wit, did you know that Dropbox is primarily written in Python? And that the same goes for Eve Online?

pace10• 15 years ago

Thanks for the great overview

JanezStupar4• 15 years ago

And this were all the factors that got me into Python when I was pondering whether to go down the Rails or Python road, when I wanted to crossover.

And I was carrying quite a torch for Ruby before. But when you realize how much broader Python is - Ruby doesn't look that good any more, no matter the hype.

brandall10• 15 years ago

"The thing is, Python's been around for a long time -- longer than Java"

So has Ruby. It just didn't catch on until Rails.

joeyespo• 15 years ago

> but is generally quieter about it

As someone who uses Python (as well as C# and various others where appropriate) often outside work, this has been exactly my experience.

I only recently discovered a Python meetup in my area and have been extremely impressed with everybody there.

Python is an amazing language with a powerful module system and vast community to rapidly prototype and research almost anything. That said, I care less about its "beauty" and more about its minimalist, lack-of-magic Pythonic philosophy backing the language that lets me get things done quickly and collaborate with others with little overhead.

ludwigvan3• 15 years ago

Google, the search engine, was written in Python for a period of time, after an initial attempt in Java.

See http://www.quora.com/Code-Quality/What-was-the-code-quality-...

rglullis• 15 years ago

In regards to your second edit: http://www.google.de/trends?q=django%2C+ruby+on+rails%2C+nod...

pace10• 15 years ago

good point but check http://en.wikipedia.org/wiki/Django Django is more than a web framework, thus I searched for "Python Django"

ak217• 15 years ago

I know many more Python developers than Ruby developers (although Rails is the best MVC framework I know of).

My personal opinion, though, is that Python is and will continue to grow in popularity because of its emphasis on what I call "cognitive compatibility" - very strong emphasis on readability and consistency. The Ruby community doesn't have the same commitment.

Ogre• 15 years ago

At my workplace (a large game developer), Python is one of three or four primary languages we use for everything. C++ for the games themselves, C# for UI heavy tools (this is relatively recent, C++ is also still used for a lot of tools), and Python for gluing it all together. (Lua would be the fourth, for in-engine scripting only).

In my world, Python replaced Perl as the language of choice for anything in a very broad "miscellaneous" category of tools. Mostly that happened 10 years ago, I haven't seen any Perl in a long, long time. Additionally, as it makes more sense to have web-based tools for certain things, Django has found its way in too. Since Python already has a strong foothold, Django makes a lot more sense in our environment than Rails.

I can find a smattering of things in other languages in our code bases, including Ruby and Erlang, but for the most part Python is the language of choice for things that aren't actual game code or Windows tools.

ludwigvan3• 15 years ago

Python and Django developer here. So you have met one more!

Interestingly, though, I find Ruby more beautiful. Possibly one of the reasons for that is it inherits a lot from the UNIX culture awk, perl roots; and also much more from Lisp and Smalltalk.

Also, my observation is that Ruby seems again very popular for OS X / Linux devs, but for Python, developers using Windows is significant. (I am not claiming that Ruby is more popular than Python for Unix users, though, just that the percentage of Windows Python users is more than Windows Ruby users.)

Rails community is definitely greater for web development as you said. One of the major differences is 37Signals, and they do a great job in pushing the project forward. The Rails project also includes several important assets which Django leaves to the developer. For example, there is no builtin migrations for Django (though most people use South), no builtin API support (tastypie/piston is commonly used).

The upside of Django is probably that things are more clear since there is less convention. This is also in accord with the languages, Python is more explicit, Ruby more magical.

One other difference that comes to my mind is that some prominent developers, like the Pragmatic Programmers Dave Thomas, or Thoughtworks' Martin Fowler prefer Ruby, while there doesn't seem to be such prominent vocal authorities speaking for Python.

pace10• 15 years ago

great comment clarifying the discussion

gbog2• 15 years ago

Peter Norvig is a prominent guy speaking for Python.

Sorry but your comment seem weird to me. If you prefer Ruby why don't you go Ruby? Great makers should love their tools.

jrockway3• 15 years ago

I would say that the opposite is true; Ruby on Rails is hyped in the startup community, but Python has a lot more real-world traction. Not every programming task is to build a web application, after all. scipy is a particularly popular application of Python.

I will agree that the Python culture is very different than the Perl or Ruby cultures. Python is a bunch of scientists and bankers writing private software for themselves and not talking much about it. Ruby is a bunch of designers making open-source projects with pretty logos and talking about them constantly. And Perl is a bunch of people that did all this 10 years ago and wonder why everyone is so excited about fast math libraries or web app frameworks.

run4yourlives• 15 years ago

Yeah, but the difference is both Pythonista's and Rubyist's can read the code after they write it. :)

tingletech• 15 years ago

re: "rising star" demonstrated with google trends search of "python django, ruby rails, node.js"

I don't think is quite right; I never hear people say "python django" whereas I do hear "ruby on rails" at least as often as "rails". Note also rails is a general term and django is either the web framework or the jazz artist it is named after.

Not that I think this google trends data really mean that much, I think the following queries give context to help interpret the meaning of the parent's link.

"python, ruby, javascript" http://www.google.de/trends?q=python%2C+ruby%2C+javascript&#...

"django, ruby rails, node.js" http://www.google.de/trends?q=django%2C+ruby+rails%2C+node.j...

"django, Django Reinhardt" http://www.google.de/trends?q=django%2C+Django+Reinhardt+...

[edit, corrected link]

[edit: someone else make the same point several hours ago, and this argument was not persuasive http://news.ycombinator.com/item?id=3277694 I just can't see making a serious decisions based on google search trends unless your job is SEO or something like that]

pace10• 15 years ago

Ok I must admit that my original G-Trends queries don't help a lot but give a least some tendency. Your queries have also shortcoming in giving a good context: don't forget Django is a very popular word, just check Wikipedia and remember the very popular movie among lots of meanings.

tsm• 15 years ago

I know Python (and Lisp and Java), and have been looking for a summer internship. There was recently a startup fair in my hometown...and of the five or so internships available, 100% of them require Ruby (and Rails), 0% really care about Python (or any other language I know).

I know Python has a huge userbase and has tons of software written in it...but it doesn't seem to be too trendy right now.

pace10• 15 years ago

That's the point: "but it doesn't seem to be too trendy right now" and still, it's pops up every 2nd day here on HN. I am fine with Clojure, Haskell and the new functional trend but just don't get it with Python.

gren• 15 years ago

Not convinced by this one: http://facts.learnpython.org/1004

RyanMcGreal2• 15 years ago

I prefer:

    [int(x) for x in "10 20 30".split(' ')]

omaranto• 15 years ago

Why? It's longer and requires an extra check to make sure that it's the same variable mentioned twice (i.e., you read to read it carefully to distinguish from [int(x) for y in "10 20 30".split(' ')]). Is it just that since comprehensions are more commonly used you think some people might forget what map does nad have to look it up?

trafficlight• 15 years ago

This one doesn't give me any output.

ThePawnBreak• 15 years ago

You need to print the value.

brown9-2• 15 years ago

Love this idea, I think one small way to look some snippets look nicer would be to remove the absolute width/height on the snippet text box (to prevent the need for scrollbars).

michaelschade2• 15 years ago

Neat project. One critique: I don't like having only five lines of the snippet visible at any given time, it makes it harder to easily understand what's going on in some of your longer snippets.

I suspect that the five line limitation was done so that the "Give me another one!" button was always in relatively the same place and easily clickable (I appreciate that), but perhaps there could be a small, duplicate text link up above the snippet for this purpose too, thereby also letting you make the snippets longer.

ronreiter9• 15 years ago

I like the idea. Yes, there's the need for both. I'm thinking about just making the text size variable according to the number of lines in the snippet - I think that makes more sense.

michaelschade2• 15 years ago

That's a thought, but even moderately sized snippets might get hard to read. I think this concern is especially valid because the rest of the text on the site is large and easily readable from a distance, so making the most important text–the snippet–smaller would be out of place.

pietro• 15 years ago

Just change the layout. The 'play' button and execution results are equally logically placed under the code. That should give you enough space for snippets of any size.

ryall• 15 years ago

Just make the area re-sizable. That way you can flick through them easily, but re-size ones you want to study.

antirez• 15 years ago

"While passing a single value to string formatting works, it's dangerous and can fail in subtle ways". AKA Python design errors.

irahul2• 15 years ago

> it's dangerous and can fail in subtle way

The only subtle way it fails, which I can think of is:

    In [27]: foo = (1,2)

    In [28]: '%s' % foo
    ---------------------------------------------------------------------------
    TypeError                                 Traceback (most recent call last)
    ----> 1 '%s' % foo

    TypeError: not all arguments converted during string formatting

jrockway3• 15 years ago

And, that's easy to fix:

   '%s' % (foo,)

Ugly, but you can be safe if you don't mind three more bytes of source code.

msinghai• 15 years ago

Works fine, except that scrolling doesn't work on an iPad.

bnegreve• 15 years ago

When I click play it says "Error!"

running debian linux with ff 3.5

kmfrk• 15 years ago

Same on Windows 7 x64 with the latest version of Opera.

EDIT: Safari, too.

test5625• 15 years ago

"Error!" in Opera 11.52 and Internet Explorer 6.0 on Windows XP.

kisielk2• 15 years ago

A bit of a nitpick, but it would be nice if the facts were PEP8 compliant so they encouraged good code style as well as showing off Python features.

ronreiter9• 15 years ago

i'm doing my best to moderate them, but you know how it works...

drx• 15 years ago

Try https://github.com/jcrocholl/pep8

You could show the output of this to the submitter (somewhat bad -- barrier to submission) or flag them yourself so you can correct them occasionally.

Examples:

  $ pep8 optparse.py
  optparse.py:69:11: E401 multiple imports on one line
  optparse.py:77:1: E302 expected 2 blank lines, found 1
  optparse.py:88:5: E301 expected 1 blank line, found 0


  $ pep8 --show-source --show-pep8 testsuite/E111.py
  testsuite/E111.py:2:3: E111 indentation is not a multiple of four
    print x
    ^
      Use 4 spaces per indentation level.

      For really old code that you don't want to mess up, you can
      continue to use 8-space tabs.

mapleoin2• 15 years ago

So then you could add something like a 'report' button to allow users to say what they think is mistaken.

shenberg4• 15 years ago

I'm not sure I agree - if it helps get the point of the snippet across more succinctly, it's worth breaking the guidelines.

cbo• 15 years ago

Not just PEP8-compliant. Some of these are just plain bad.

The first one I was greeted with when I opened the site was:

> print eval('+'.join(map(str, [1, 1])))

If I ever saw this in production code, I would lose my mind.

It's the kind of one-liner I'd expect to find in an obfuscated code competition. It's not intuitively understood, shows a lack of basic Python functionality (the builtin sum() function), and most of all, it's SLOW. As in, 54 times slower than a simple sum -- tested on xrange(1,10) -- on my development Macbook Pro.

That said, clicking through some other examples, there are a lot of great Python examples on this site. Just beware of some of them, and always make sure you test new code yourself.

shenberg4• 15 years ago

I'm pretty sure that one-liner is a joke...

gbog2• 15 years ago

Slowness is not the worst, eval is evil, and should be forbidden, that's all.

codecaine• 15 years ago

added this to my start tabs

rhdoenges2• 15 years ago

> How can addition be more easier than this?

    print eval('+'.join(map(str, [1, 1])))

Seriously?

ronreiter9• 15 years ago

It's a joke :)

rhdoenges2• 15 years ago

phew :)

agscala• 15 years ago

I ran into this one first and started to wonder if the whole site was a joke

Rexxar• 15 years ago

Bug at the third try: http://facts.learnpython.org/7006

    Output:
    Traceback (most recent call last):
      File "/base/data/home/apps/s~learnpythonjail/1.350338289496947596/main.py", line 99, in post
        exec(cmd, safe_globals)
      File "<string>", line 2, in <module>
    TypeError: 'start' is an invalid keyword argument for this function

shenberg4• 15 years ago

The start argument was only added in Python 2.6...

gcr• 15 years ago

Nice project, but you NEED some sandboxing.

  import os
  print os.listdir('.')
  print open('turtle.py').read()

Edit: It seems like you're doing some; i can't inspect any directories outside the "jail", but being able to list the source code of your scripts is a security risk.

shenberg4• 15 years ago

Python had an implementation of sandboxing (rexec), but gave up plugging the holes people kept finding in it (see http://docs.python.org/library/rexec.html).

The problem is that sandboxing wasn't designed into the language so they don't give users a false sense of security with a bad sandbox.

To see the legacy of the sandbox, open an interpreter and run 'del __builtins__' to activate the restricted execution mode. Now, a lot of simple things like the import statement should fail. A good exercise in python internals is to manage to execute unrestricted code from this state via clever use of introspection.

Note: 'del __builtins__' is more than just removing access to builtin objects:

  >>> f = file
  >>> del __builtins__
  >>> f('a.txt','w')
  Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
  IOError: file() constructor not accessible in restricted mode

domlebo70• 15 years ago

Would anyone be interested in something like this for Scala?

hardik988• 15 years ago

A small bug: Go on any random fact, eg: http://facts.learnpython.org/3007 Click on "Add your own", and then click go Back in your browser. The snippet is blank. This is Chrome 15 on Windows 7.

kisielk2• 15 years ago

Sorry, I think I broke your site. I realized based on one of the comments here that you seem to be running a persistent interpreter and then just running the code snippets. So I decided to see what would happen if I changed one of them...

So I found the snipped that did something like

import collections foo = collections.defaultdict

and added

collections.defaultdict = None

to the end of it.

Next time I ran it the original snippet just gave a stack trace. Oops :) Anyway, looks like you need to work on sandboxing the snippets some more.

I would have sent this to you via email or other means, but I couldn't find any other way to contact you in your HN profile or on your site.

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