Serializing YAML with PyYAML

Internal

• YAML in Python

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:

YAML in Python | Representer

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)