[FIXED] How to initialize yaml parser/loader/dumper for a class

Issue

I want to initialize yaml with following parameters

from ruamel.yaml import YAML
...
def null_representer(self, data):
    return self.represent_scalar(u'tag:yaml.org,2002:null', u'null')

yaml = YAML()
yaml.representer.ignore_aliases = lambda *data: True
yaml.indent(mapping=2, sequence=4, offset=2)
yaml.preserve_quotes = True
yaml.representer.add_representer(type(None), null_representer)

I wanted to know if there's a way I can initialize yaml like this to use in my class

class A:
   def __init__(self):
        self._yaml = (the yaml I initialized)

For example, python logging module has this fucntion -

import logging

def init_logging():
    log = logging.getLogger()
    log.setLevel(logging.INFO)
    sh = logging.StreamHandler()
    formatter = logging.Formatter('%(asctime)s - %(levelname)s - %(message)s', datefmt='%Y-%m-%d %H:%M:%S')
    sh.setFormatter(formatter)
    log.addHandler(sh)

class A:
   def __init__(self):
        self._log = logging.getLogger('A')

Solution

If you want the YAML() instance to be the global one that you already initialised, and class A is anywhere in the same file, you can just do

def __init__(self):
    self._yaml = yaml

as long as you don't make an instance of A before yaml is assigned to.

If you have the class A in a different file, just import yaml from the Python file, just like you import getLogger. E.g. if the first code block is in myyaml.py:

from util.myyaml import yaml

Make sure you have (an empty) __init__.py files in the subdirectory util

Of course you can also give an instance of class A its own YAML() instance:

from ruamel.yaml import YAML

def null_representer(self, data):
    return self.represent_scalar(u'tag:yaml.org,2002:null', u'null')

class A:
   def __init__(self):
       self.yaml.load(.....)

   @property
   def yaml(self):
       try:
           return self._yaml
       except AttributeError:
           pass
       self._yaml = yaml = YAML()
       yaml.representer.ignore_aliases = lambda *data: True
       yaml.indent(mapping=2, sequence=4, offset=2)
       yaml.preserve_quotes = True
       yaml.representer.add_representer(type(None), null_representer)
       return yaml

This is the way I usually do things. If self.yaml is not used in the __init__(), the instantiation of YAML() will be delayed until you first use it, which might speed up your program startup.

Answered By - Anthon

Answer Checked By - Robin (PHPFixing Admin)