Wednesday, November 02, 2016

Python Usability Bugs: Formatting argparse subcommands

Suppose you want to build a tool with a simple interface:
usage: sub <command>

commands:

  status -  show status
  list   -  print list
Python proposes to use argparse module. And if you follow documentation, the best you can get will be this output:
usage: sub {status,list} ...

positional arguments:
  {status,list}
    status       show status
    list         print list
And it you implement proper formatting, your code will look like this:
import argparse
import sys

class CustomHelpFormatter(argparse.HelpFormatter):
  def _format_action(self, action):
    if type(action) == argparse._SubParsersAction:
      # inject new class variable for subcommand formatting
      subactions = action._get_subactions()
      invocations = [self._format_action_invocation(a) for a in subactions]
      self._subcommand_max_length = max(len(i) for i in invocations)

    if type(action) == argparse._SubParsersAction._ChoicesPseudoAction:
      # format subcommand help line
      subcommand = self._format_action_invocation(action) # type: str
      width = self._subcommand_max_length
      help_text = ""
      if action.help:
          help_text = self._expand_help(action)
      return "  {:{width}} -  {}\n".format(subcommand, help_text, width=width)

    elif type(action) == argparse._SubParsersAction:
      # process subcommand help section
      msg = '\n'
      for subaction in action._get_subactions():
          msg += self._format_action(subaction)
      return msg
    else:
      return super(CustomHelpFormatter, self)._format_action(action)


def check():
  print("status")
  return 0

parser = argparse.ArgumentParser(usage="sub <command>", add_help=False,
             formatter_class=CustomHelpFormatter)

subparser = parser.add_subparsers(dest="cmd")
subparser.add_parser('status', help='show status')
subparser.add_parser('list', help='print list')

# custom help messge
parser._positionals.title = "commands"

# hack to show help when no arguments supplied
if len(sys.argv) == 1:
  parser.print_help()
  sys.exit(0)

args = parser.parse_args()

if args.cmd == 'list':
  print('list')
elif args.cmd == 'status':
  sys.exit(check())

Here you may see the failure of OOP (object oriented programming). The proper answer to this formatting problem is just to define a data structure for command line help in JSON or similar format and let people dump and process it with templates. Once option definition is parsed, the information there is static, so there is no need in those intertwined recursive method calls. So just do it in 2 pass - get dataset and render template.

Saturday, September 17, 2016

Python Usability Bugs: subprocess.Popen executable

subprocess.Popen seems to be designed as a "swiss army knife" of managing external processes, and while the task is pretty hard to solve in cross-platform way, it seems the people who have contributed to it did manage to achieve that. But it still came with some drawbacks and complications. Let's study one of these that I think is a top one from usability point of view, because it confuses people a lot.

I've got a simple program that prints its name and own arguments (forgive me for Windows code, as I was debugging the issue on Windows, but this works the same on Linux too). The program is written in Go to get single executable, because subprocess has special handling for child Python processes (another usability bug for another time).
>argi.exe 1 2 3 4
prog: E:\argi.exe
args: [1 2 3 4]
Let's execute it with subprocess.Popen, and for that I almost always look up the official documentation for Popen prototype:
subprocess.Popen(argsbufsize=0executable=Nonestdin=None, stdout=Nonestderr=Nonepreexec_fn=Noneclose_fds=False, shell=Falsecwd=Noneenv=Noneuniversal_newlines=False, startupinfo=Nonecreationflags=0)
Quite scary, right? But let's skip confusing part and quickly figure out something out of it (because time is scarce). Looks like this should do the trick:
import subprocess

args = "1 2 3 4".split()
p = subprocess.Popen(args, executable="argi.exe")
p.communicate()
After saving this code to "subs.py" and running it, you'd probably expect something like this :
> python subs.py
prog: E:\argi.exe
args: [1 2 3 4]
And... you won't get this. What you get is this:
> python subs.py
prog: 1
args: [2 3 4]
And that's kind of crazy - not only the executable was renamed, but the first argument was lost, and it appears that this is actually a documented behavior. So let's define Python Usability Bug as something that is documented but not expected (by most folks who is going to read the code). The trick to get code do what is expected is never use executable argument to subprocess.Popen:
import subprocess

args = "1 2 3 4".split()
args.insert(0, "argi.exe")
p = subprocess.Popen(args)
p.communicate()
>python suby.py
prog: argi.exe
args: [1 2 3 4]
The explanation for former "misbehavior" is that executable is a hack that allows to rename program when running subprocess. It should be named substitute, or - even better - altname to work as an alternative name to pass to child process (instead of providing alternative executable for the former name). To make subprocess.Popen even more intuitive, the args argument should have been named command.

From the high level design point of view, the drawbacks of this function is that it *does way too much*, its arguments are not always intuitive - it takes *a lot of time to grok official docs*, and I need to read it *every time*, because there are too many little important details of Popen behavior (have anybody tried to create its state machine?), so over the last 5 years I still discover various problems with it. Today I just wanted to save you some hours that I've wasted myself while debugging pymake on Windows.

That's it for now. Bonus points to update this post with link when I get more time / mana for it:

  • [ ] people who have contributed to it
  • [ ] it came with drawbacks
  • [ ] have anybody tried to create its state machine?
  • [ ] subprocess has special handling for child Python processes

Thursday, June 16, 2016

Why Python community should take UX seriously

UX is a discipline that is dedicated to measuring user emotions and satisfaction while using a product in order to improve them. When you grow experience in any programming language you start to experience negative emotions towards small warts and glitches that constantly get in your way. You compare it to different languages and soon you're no more satisfied with it. Backward compatibility etc. doesn't allow to change things, but they should be changed, and UX is the criteria and method to answer how. But why?

People are dying too quickly. The process of learning new technology is fun and exciting, but when you look at the ideas in the past you'll see that we are not inventing anything new. People thought about many ideas, and couldn't implement them. I still don't have automation line that pours me coffee in the morning and bakes omelet and this idea is like 20 years old. I have no information about where my products are coming from - this idea is about 10 years old, and those fruits that are coming from hydroponics and pretty tasteless, so I'd prefer to buy something bathed in organic sun. Where are those inventions now? I am pretty sure somebody is trying to design these things in own basement, but those inventions will never see the light, because they are fragile, needs a lot of experience and education. Why learning is hard? It needs a lot of experience and education to learn concepts, operating systems internals and get used to various glitches and workarounds from the past. If Python was easier, if operating systems were more easy to learn and intuitively understand, not relying on elitist part of hacker culture, we could hack on more fun and reliable things today.

Tuesday, June 07, 2016

Why Roundup needs a router?

http://bugs.python.org/ is powered by ancient software. Most people nowadays won't install it. They would rather find something newer, with more features (consumers) or invent something from scratch that will be more modern from the start (makers).

How about trying a different approach - how about an approach that means constant evolution of the software? The reason why people reinvent things from scratch is because they often can not understand the complexity of what was already written. The burden of complexity is like tar that glues us to the surface, needs more force to take a step and slows us down. One way to get rid of it is to start again clean. But there is no guarantee that the same story won't happen if you couldn't see past complexity before.

A way of evolution is to face the complexity and deal with it. The way to deal with complexity tar is to learn to fly over it. Visualization, art, story-telling are helping to people to overcome limitations of our attention, interest, motivation and focus. There are tools to make complex things simple, there are things to look at the surface from above and choose a path that is still unexplored.

Router is a component that directs URL request to processing. Router says that http://../file142 should be processed by function that handles files, and http://../issue42 should be handled by function that processes issues. This logic is hardcoded into Roundup, so its URL structure doesn't change. If Roundup had this router, then it could be used as a replacement for existing trackers without breaking links. Router also allows Roundup extensions add new endpoints, such as ones required for OAuth2 processing or REST and ajax interface.

So, how to evolve software? It takes media and coordination skills first, and code review and design second. Additional code that makes code more complex should be backed up by documentation that explains it, every lengthy documentation that gives details should be accompanied by concise overview and reminder picture, every yak shaving process should be automated, every upstream tools need to be improved. Evolution is a global process, and it is hard (if not impossible) to evolve one agent if the whole ecosystem is not changing. Changing ecosystem or tools that are already stable like Python require process shift that drastically changes how people coordinate, approve, mutate and select the branches with features that comfort them.

Wednesday, May 11, 2016

Open Source, Death, and Open Economy

Open Source is a great idea, great movement and a great boost to the progress of civilization. Open Data made transparent governments possible, which allowed people to regulate tough problems, not hide them. Open systems like Linux and Open Stack enabled building more useful software on top of more solid and stable basis (first for single operating system nodes and now for clouds and networks).

So why Open Source is dead? Because there is no such thing as software product - any software is alive as long as its code is live in the heads of its maintainers. As soon as maintainers leave, the product enters death spiral - new people enter the field to patch the product to the death. Open Source is dead, because maintaining Open Source software requires time, and every minute of that time you need to pay for food, for shelter, for the privilege to meet with your friends and be inspired. Open Source maintenance does not release maintainers from paying for all this stuff and doesn't bring them those payment tokens called `money`. So code in maintainers heads will have to die.

How come that current economy is so flawed? Does Open Source produce value? Definitely, yes. Does it solve problems for people? Yes. Do people feel grateful for Open Source? Well, sometimes (but that's also the question of consumer culture forced by current economy). And still open source developers leave their products to join (often meaningless) activities of reinventing things from scratch for other projects. Often doing things that they've paid for and not things they know and like.

How come that people with developed skills doing useful things have nothing to eat, and for food and shelter have to reformat their brain and became compliant with office slavery? Sometimes I feel like we should extend software freedom conservancy model from software to people and remove "people with money" from power part of this equation. Blockchain allows us to calculate personal values to remove this money-for-money gameplay. Gameplay that creates parasites out of people, parasites that are motivated to produce garbage, to consume and to battle each other for "market domination". Parasites don't like to be exposed, and they don't like to be parasites, so maybe Open Economy is an answer that can bring our focus back to the planet with depleting resources and increasing pollution that pushes our health and general feeling of the world down to the level of committing a suicide.

I'd like to believe, but I am loosing my insight sometimes. There are many good people who care about me in this world, and this letter won't be there if not them. But their lifetime is limited, and so is mine. I really wanted to boost progress to help with my health and global problems, but it seems I failed. This post is filled under a Python tag, which always was a part of that unconscious plan. I thought that I could enhance it to be an easier, and more intuitive tool to augment limited human abilities for automation, to help them concentrate on more important things. But it seems I failed. I still see things how they should be done, I still see that DX (developer's experience) need to raise to the top of people priorities. It is just that I am exhausted to compete for food and shelter and feel depressed over the need to reformat my natural intelligence network to do those (often meaningless) office things just to keep my body alive.

Sunday, January 10, 2016

Reaction to Python development moving to GitHub

If you don't know, the Python core developers are considering move to GitHub, which I believe will abandon Roundup, Mercurial and a couple of other initiatives that some of us picked, because they were used by community and were useful to it. For example I added support for Jinja2 to Roundup, tried to add a new router component for it to enable adding new web APIs more easily, and now I am doing a release of new version, because that package is valuable.

Below is my post sent to https://mail.python.org/mailman/listinfo/core-workflow as an immediate reaction to the PEP that addresses the migration. I think that people need to consider Python as something with much better potential than just "a product to execute computer scripts". I want people to think about it as about open process with all the involved complexity and dynamics issues, a place to study and learn about different culture than following the orders of your owner founder. Some want to see it to be isolated coding playground without all that disturbances and annoying people with external world problems. But it is unavoidable. There are already diversity statement and codes of conducts. It is time to stop being ignorant to economics for the balance.

Blender is a good example. 3D editor that every two years chooses a problem that is actual for community and makes a movie together with building necessary features in the editor. They discuss economics, try to address funding issues by working with funds outside of coding domain, bringing new initiatives, communicating and still staying open - not ignoring the issues and not trying to bring the same hammer on the new "nail". Why Python fails to follow the same route?

I don't know why it bother me that much. Probably because I am jobless and living in northern country where you can't live on street and need to pay rent, so "getting paid for the useful stuff that you do" is extremely important issue for me. But also I feel that my time is limited, and that it is very sad to spend my life behind the screen of computer, reinventing some code that was written numerous time for a company that can not support something that is already written.

I realize that with reduced exposure to a projects like Roundup and Mercurial it will be much harder (if possible at all) to gather critical mass of resources around people to experiment with sustainability models for open source, and doing these things is important, because we coming into the age of extremely powerful automation where people may not be that needed anymore. For me open source is the only way to gather data on what will happen, and maybe the only way to find the balance. Open source economics right now is when resources are limited, but there are many people how could use them, but if they use them, others (who probably can do better) may feel bad about this. This is a just a single problem that needs to be addressed in the process, and I wish that there could be that sustainable working process in the list.

Here is original mail sent:


Thursday, September 03, 2015

SCons build targets

SCons is awesome. Just saying. If you want to know (or troubleshoot) how SCons selects targets to be built, add this snippet at the end of your SConstruct:
def dump_targets(targets):
  for t in targets:
    if type(t) == str:
      name = t
    else:
      name = t.name
    print("  <" + str(t.__class__.__name__) + "> " + name)

print("[*] Default targets:")
dump_targets(DEFAULT_TARGETS)

print("[*] Command line targets:")
dump_targets(COMMAND_LINE_TARGETS)
print("[*] All build targets:") dump_targets(BUILD_TARGETS)
For my copy of Wesnoth, 'scons .' produces this output:
[*] Default targets:
  <Alias> wesnoth
  <Alias> wesnothd
[*] Command line targets:
  <str> .
[*] All build targets:
  <str> .
And if you want to know how to specify targets or what do they mean, read the second page of SCons man documentation. Just for convenience I quote it here.



scons is normally executed in a top-level directory containing a SConstruct file, optionally specifying as command-line arguments the target file or files to be built.

By default, the command
scons
will build all target files in or below the current directory. Explicit default targets (to be built when no targets are specified on the command line) may be defined the SConscript file(s) using the Default() function, described below.

Even when Default() targets are specified in the SConscript file(s), all target files in or below the current directory may be built by explicitly specifying the current directory (.) as a command-line target:
scons .
Building all target files, including any files outside of the current directory, may be specified by supplying a command-line target of the root directory (on POSIX systems):
scons /
or the path name(s) of the volume(s) in which all the targets should be built (on Windows systems):
scons C:\ D:\
To build only specific targets, supply them as command-line arguments:
scons foo bar
in which case only the specified targets will be built (along with any derived files on which they depend).

Specifying "cleanup" targets in SConscript files is not usually necessary. The -c flag removes all files necessary to build the specified target:
scons -c .
to remove all target files, or:
scons -c build export
to remove target files under build and export. Additional files or directories to remove can be specified using the Clean() function. Conversely, targets that would normally be removed by the -c invocation can be prevented from being removed by using the NoClean() function.

A subset of a hierarchical tree may be built by remaining at the top-level directory (where the SConstruct file lives) and specifying the subdirectory as the target to be built:
scons src/subdir
or by changing directory and invoking scons with the -u option, which traverses up the directory hierarchy until it finds the SConstruct file, and then builds targets relatively to the current subdirectory:
cd src/subdir
scons -u .