Making it easier to use libyaml in PyYAML

[edemaine@…]

I really like PyYAML with the libyaml "plugin". I've been using it a lot without any troubles. So hopefully it will make it out of alpha soon :-). I have a couple of suggestions with respect to seamlessness between PyYAML in Python mode and PyYAML in C mode.

1. yaml.load's default Loader. I would suggest that this becomes CLoader when it is available (i.e., when yaml.cyaml imports successfully).

2. yaml.dump's and yaml.safe_dump's default Dumpers. Ditto.

3. Loader vs. CLoader, Dumper vs. CDumper, Emitter vs. CEmitter, etc. I would like a uniform way (without using if's) to subclass from the C version of these classes when they are available, and otherwise the Python versions of these classes. One possible solution:

• Python Loader etc. classes get renamed to PyLoader, PythonLoader, PLoader, or something along those lines.
• Loader becomes an alias to CLoader or PyLoader, whichever is the best available.
• It could also be possible to control the aliases by a function call, e.g., to force them to the Python version. Perhaps:

  def set_language(lang):
    """default supported languages: 'C', 'Python'"""
    import yaml
    global Loader, Dumper, Emitter, ...
    Loader = yaml.__dict__[lang + 'Loader']
    Dumper = yaml.__dict__[lang + 'Dumper']
    Emitter = yaml.__dict__[lang + 'Emitter']
    ...
  try:
    set_language('C')
  except KeyError:
    set_language('Py')
  

Currently all of my code that imports yaml starts like this:

import yaml
if hasattr (yaml, 'CLoader'):
  Loader = yaml.CLoader
else:
  Loader = yaml.Loader
if hasattr (yaml, 'CDumper'):
  Dumper = yaml.CDumper
  SafeDumper = yaml.CSafeDumper
else:
  Dumper = yaml.Dumper
  SafeDumper = yaml.SafeDumper
def yaml_load (x):
  return yaml.load (x, Loader = Loader)
def yaml_dump (x):
  return yaml.dump (x, Dumper = Dumper)
def yaml_safe_dump (x):
  return yaml.dump (x, Dumper = SafeDumper)

Then I use yaml_load in place of yaml.load, yaml_dump in place of yaml.dump, and I use Loader etc. whenever I want to subclass. Needless to say, it's annoying to have to repeat this in all of my projects.

Another motivation for all this, I think, is that it's not obvious out-of-the-box how to use CLoader and friends. I don't think the average user should have to know about this distinction. If libyaml is installed, it should just work (faster).

A more minor point: Once out of alpha, could we replace setup.py and setup_with_libyaml.py with a single setup.py that does the right thing depending on what's available in the environment? (If PyRex? is installed, I don't see why we shouldn't install, unless a command-line option tells us not to. Or even if RyRex? isn't installed, as suggested in anotehr ticket.)

[xi]

The updated setup.py detects if libyaml is installed and builds the bindings automatically.

[Laurens]

I agree with the original poster: I thought that by installing the windows python bindings (which include libyaml), pyyaml would use those libraries. Only when investigating why my yamlloading was quite slow, I figured out I was _NOT_ using libyaml bindings.

So, I definately second the request to use libyamlbindings by default if available.

If that's not possible, please change the documentation so that "In order to use LibYAML based parser and emitter, use the classes CParser and CEmitter." in http://pyyaml.org/wiki/PyYAMLDocumentation is not listed under 'Installation'; this is not about installation, it's about usage. I missed it for that reason: I had it already installed, so I didn't think I needed to read the installation-documentation.

[anonymous]

Replying to Laurens:

I agree with the original poster: I thought that by installing the windows python bindings (which include libyaml), pyyaml would use those libraries. Only when investigating why my yamlloading was quite slow, I figured out I was _NOT_ using libyaml bindings. So, I definately second the request to use libyamlbindings by default if available. If that's not possible, please change the documentation so that "In order to use LibYAML based parser and emitter, use the classes CParser and CEmitter." in http://pyyaml.org/wiki/PyYAMLDocumentation is not listed under 'Installation'; this is not about installation, it's about usage. I missed it for that reason: I had it already installed, so I didn't think I needed to read the installation-documentation.

+1