Reworder – A tale of learning Python and launching an app in five days. | Hacker News Reader

Reworder – A tale of learning Python and launching an app in five days.

sahillavingia.com

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make sure you use tabs to format all of your Python code

I disagree. Idiomatic Python uses 4 spaces per indent.

Either solely use tabs or solely use spaces, they don’t work well together, at least in my experience

Mixing tabs and spaces is indeed very unwise. You can run Python with the -tt option to make sure you're consistent.

Read Style Guide for Python Code for more advice on this front

I agree ;-) The author probably refers to PEP8, http://www.python.org/dev/peps/pep-0008/

Ah yes, I'll read more into it! thanks :)

I was fixing a makefile the other day with a coworker and it ended up being an indentation issue. And then we asked out loud why anyone would repeat this hell again...

Now, I am not a python programmer, but I am interested to learn more about how the structure via indentation how worked out for the language.

Could not agree more!!!! If you're a vimmy, be sure to add this friendly helper into your .vimrc

:set tabstop=4

:set shiftwidth=4

:set expandtab

Or, if you only want to use these settings for python files, create a ~/.vim/ftplugin/python.vim file. Mine looks like this:

  setlocal tabstop=4
  setlocal softtabstop=4
  setlocal shiftwidth=4
  setlocal textwidth=80
  setlocal smarttab
  setlocal expandtab
  setlocal smartindent

Today I learned...

Thanks.

It looks like ftplugin is a native vim extension - is that correct?

I'm a bit late in responding, but yes, it's a native vim extension. To make sure your plugins are loaded automatically, put

  filetype plugin on

in your .vimrc.

  Traceback (most recent call last):
    File "/base/python_runtime/python_lib/versions/1/google/appengine/ext/webapp/__init__.py", line 513, in __call__
      handler.post(*groups)
    File "/base/data/home/apps/reworder/1.345779356045891791/reworder.py", line 122, in post
      headers={'Content-Type': 'application/x-www-form-urlencoded'}).content)
    File "/base/python_runtime/python_lib/versions/third_party/django-0.96/django/utils/simplejson/__init__.py", line 232, in loads
      return cls(encoding=encoding, **kw).decode(s)
    File "/base/python_runtime/python_lib/versions/third_party/django-0.96/django/utils/simplejson/decoder.py", line 251, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
    File "/base/python_runtime/python_lib/versions/third_party/django-0.96/django/utils/simplejson/decoder.py", line 270, in raw_decode
      raise ValueError("No JSON object could be decoded")
  ValueError: No JSON object could be decoded

Entered text "this is a test." and hit submit.

Figured out the bug: hit the API request limit. Argh!

    Traceback (most recent call last):
      File "/base/python_runtime/python_lib/versions/1/google/appengine/ext/webapp/__init__.py", line 513, in __call__
        handler.post(*groups)
      File "/base/data/home/apps/reworder/1.345779356045891791/reworder.py", line 140, in post
        synonym = synonym_for_word(stripped_word, tag)
      File "/base/data/home/apps/reworder/1.345779356045891791/reworder.py", line 201, in synonym_for_word
        return result.get(word_type)['syn'][0]
    KeyError: 'syn'

Hence, Teach Yourself Programming in Ten Years[1]. All kidding aside, I'm pretty sure it's unrelated to the actual code :)

[1] http://norvig.com/21-days.html

"I was already pretty dead set on learning a functional language (either Python or Ruby)"

Did I see something strange here?

He meant javscript. A common typo.

Eh? How is Javascript any more functional than Python or Ruby?

He said he wanted to learn a functional language, and then listed Python and Ruby. Weird.

There's a joke here I don't get. Care to explain? :D

Python and Ruby aren't functional languages.

You can write code in them in a functional manner, but for anything more than toy programs you _likely_ wouldn't.

They're heavily Object-Oriented, but could probably safely be called multi-paradigm. Not just "functional", though.

Functional languages are Haskell, ML, others, where you express computation by composing functions (in the mathematical sense). You make lots of copies and you don't modify state directly like procedural and OO languages do where you modify state a lot.

I remember it took me a dozen times of carefully reading explanations like this before I finally got what "functional" meant... I'll try to provide an explanation my former self would have easily got.

  lambda x: x+1

If you only program with lambda's like these, your program is functional.

  def dosomething(x):
      y = x + 3 # y is a global variable
      return x + 1

As soon as you have a function like this, your program is no longer 100% functional.

The dosomething function modified `state` when it changed a global variable. Another function that modifies state is "print()". Generally any function that returns nothing is almost certainly going to modify state outside of it. (Otherwise what is the function for?)

State is memory that is not `local` to the function itself.

  def dosomething(x):
      y = x + 3 # y is a local variable
      return x + 1

The dosomething function here is functional, because the only `state` it modified was local to the function.

There you have it.

Even more simply - are you writing code for a von Neumann architecture (http://en.wikipedia.org/wiki/Von_Neumann_architecture ), or something more abstract?

To my understanding the issue is not whether "state" has side effects (e.g. your global vs. local example), but rather whether there is any concept of "state" (e.g. shuffling stuff from one memory slot to another).

My experience is from Prolog, where the statement "X is X + 1" results in an error, because once unified, the variable X cannot be modified - X is not a memory slot. Once you try to let go of the idea of a machine with memory slots, alternative-paradigm programming gets a little bit easier. Of course in practice state is often needed, so it often gets added through some mechanism.

That's a good explanation.

My explanation is catered to people accustomed to the von Neumann architecture, however. :)

It's an easy mistake to make - when you come from a Java or C# background one of the most striking things about Python and Ruby code is the use of first-class functions.

Not everybody knows that there's more to a functional language than first-class functions.

Completely unrelated to your write up but theres a bug. In FF if I back up and resubmit it doesn't update to the new text. I still see my first submission.

Ah yes, I randomly generate a permalink on load of the page, so it uses the old permalink, hence why it loads the first submission. Any ideas on how to change this?

I guess just generate the permalink in the action and redirect to that instead of having it in the form itself.

Something like:

Form: /reworder/generate

Action: Generates text, creates permalink and then redirects user to that permalink.

In the web world this pattern is common, called redirect-after-post. I'm not sure if thats much help, I've only used python in the context of the Pylons framework (and have only a few days experience with it at that). If you need more guidance let me know and I'll try and clarify.

edit: Link to redirect after post: http://en.wikipedia.org/wiki/Post/Redirect/Get

edit2: I should also say this is a pretty sweet project, sorry if I just listed criticisms.

Of course not, I love criticisms. How else do I improve? I'll implement that ASAP.

"App engine is fast and awesome, right now. However, if your site gets really popular, you may consider moving off of it."

Perhaps you can explain why you believe this to be true? I thought that the strength of App Engine is that you can stay on it no matter how popular your app gets.

App engine doesn't allow certain features, like subdomains for each user, and non-www. URLs. Some other things too, that I probably don't even know about yet.

While I agree that there are limitations with App Engine, I disagree with your two examples; not only are these possible, I think they have a nice solution on App Engine.

1. Wildcard subdomains and multi-tenancy seem to be a nice solution to "subdomains for each user".

2. Unless by "non-www. URLs" you mean naked domains, that is also possible; both explicitly defined and with wildcard subdomains.

Maybe I'm misinterpreting you though.

Traceback (most recent call last): File "/base/python_runtime/python_lib/versions/1/google/appengine/ext/webapp/__init__.py", line 513, in __call__ handler.post(*groups) File "/base/data/home/apps/reworder/1.345779356045891791/reworder.py", line 140, in post synonym = synonym_for_word(stripped_word, tag) File "/base/data/home/apps/reworder/1.345779356045891791/reworder.py", line 201, in synonym_for_word return result.get(word_type)['syn'][0] KeyError: 'syn'

Awesome story. Thank you very much for the Stanford links.

Hey, weren't you supposed to be a designer :) That's pretty quick to go from 0 to launch in 5 days in an unknown language.

Congratulations!

Designer, developer, coder, sleep-deprived. I'm a dude of many properties! :)

Any input containing a forward slash results in a ValueError.

if anyone cares, rephrasing engines are used to create splogs for SEO

Breaks on apostrophes.

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