ruamel.yaml.representer.RepresenterError: cannot represent an object: {'value': }

from ruamel.yaml import YAML class Config(dict): def __init__(self, filename, auto_dump=True): self.filename = filename self.auto_dump = auto_dump self.changed = False self.yaml = YAML() self.yaml.preserve_quotes = True # uncomment and adapt to your specific indentation # self.yaml.indent(mapping=4, sequence=4, offset=2) if os.path.isfile(filename): with open(filename) as f: # use super here to avoid unnecessary write super(Config, self).update(self.yaml.load(f) or {}) def dump(self, force=False): if not self.changed and not force: return with open(self.filename, "w") as f: self.yaml.dump(self, f) self.changed = False # following methods unchanged from PyYAML example def updated(self): if self.auto_dump: self.dump(force=True) else: self.changed = True def __setitem__(self, key, value): super(Config, self).__setitem__(key, value) self.updated() def __delitem__(self, key): super(Config, self).__delitem__(key) self.updated() def update(self, kwargs): super(Config, self).update(kwargs) self.updated() cfg = Config("test.yaml") print(cfg) cfg['a'] = 3 # <=Error occurs print(cfg) cfg.update({"b": 4}) cfg.update(c=5) del cfg['a'] print(cfg)

It looks like the code in "PyYAML - Saving data to .yaml files" was not tested, normally there would be some output (which is automatically included in the answers I post).

The code almost works, but needs a cast of self to dict to get the key-value pairs, otherwise ruamel.yaml tries to dump the attributes (.filename, etc).

If you want both (dict-like) arguments as well as key-value arguments for .update() you'll need to extend it argument list:

import os
from ruamel.yaml import YAML

class Config(dict):
    def __init__(self, filename, auto_dump=True):
        self.filename = filename
        self.auto_dump = auto_dump
        self.changed = False
        self.yaml = YAML()
        self.yaml.preserve_quotes = True
        # uncomment and adapt to your specific indentation
        # self.yaml.indent(mapping=4, sequence=4, offset=2)
        if os.path.isfile(filename):
            with open(filename) as f:
                # use super here to avoid unnecessary write
                super(Config, self).update(self.yaml.load(f) or {})

    def dump(self, force=False):
        if not self.changed and not force:
            return
        with open(self.filename, "w") as f:
            self.yaml.dump(dict(self), f)
        self.changed = False

    # following methods unchanged from PyYAML example
    def updated(self):
        if self.auto_dump:
            self.dump(force=True)
        else:
            self.changed = True

    def __setitem__(self, key, value):
        super(Config, self).__setitem__(key, value)
        self.updated()

    def __delitem__(self, key):
        super(Config, self).__delitem__(key)
        self.updated()

    def update(self, *args, **kw):
        for arg in args:
            super(Config, self).update(arg)
        super(Config, self).update(**kw)
        self.updated()


cfg = Config("test.yaml")
print(cfg)
cfg['a'] = 3  # <=Error occurs
print(cfg)
cfg.update({"b": 4})
cfg.update(c=5)
del cfg['a']
print(cfg)

print('------')
print(open(cfg.filename).read())

which gives:

{}
{'a': 3}
{'b': 4, 'c': 5}
------
b: 4
c: 5

This dumps the config as if it were a dict and there is no tag in the YAML to indicate what has been dumped and nothing would help identifying during reading back of the configuration. So it would IMO be better to make this a dumpable class in the normal way and dump with a tag like !Config.

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