Serializing YAML with PyYAML
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Internal
Overview
The process of serialization to YAML is rendering an in-memory data structure as a YAML-formatted string. The simplest sequence of statements that does that is:
import yaml
data = {
'color': 'red',
'size': 10,
'parts': ['top', 'middle', 'bottom']
}
yaml_string = yaml.dump(data)
The YAML-formatted string will be:
color: red
parts:
- top
- middle
- bottom
size: 10
Customizing Output
Customizing Output with dump() Parameters
# with the default flow style, the document is rendered in a non-indented manner
print (yaml.dump(data, default_flow_style=False))
Customizing Output with Representers
The general process of using a custom representer of a data type is described here:
Configure yaml.dump() to render blank instead of null
PyYAML dump()
uses Representer()
to represent None
. By default, the representer dump()
is configured with represents None
as "null". To change that:
1. Define a method that "represents" None
def representer_for_none(self, _):
return self.represent_scalar('tag:yaml.org,2002:null', '')
2. Add it to the module:
import yaml
[...]
yaml.add_representer(type(None), represent_none)
This will render:
d = {
'a': None,
'b': 'c'
}
as:
a:
b: c
what is the lifecycle of the method registered to the module?
Configure yaml.dump() to render | multi-lines
def literal_presenter(dumper, data):
return dumper.represent_scalar('tag:yaml.org,2002:str', data, style='|')
def default_presenter(dumper, data):
return dumper.represent_scalar('tag:yaml.org,2002:str', data, style='')
try:
yaml.add_representer(str, literal_presenter)
yaml_text = yaml.dump(config)
return yaml_text
finally:
yaml.add_representer(str, default_presenter)