egeneralov / python-yaml-patch

Apply patches to a yaml string, keeping most of the formatting and comments.

yaml-patch

Apply patches to a yaml string, keeping most of the formatting and comments.

Some formatting is not kept due to underlying yaml library limitations:

• Indentation will be forced to two spaces
• Spacing before sequence dashes will be forced to two spaces
• Empty lines at the start of the string will be removed

Installation

pip install yaml-patch

As a command line tool

You can pass any number of patches to be applied, they use the following syntax options:

Override a single value:

<field>.<subfield>=<value>

Example:

yaml-patch -f test.yml "spec.replicas=2"

Override a value inside a single list item:

<field>.[<position]>.<subfield>=<value>

Example:

yaml-patch -f test.yml "spec.template.containers.[0].image='mycontainer:latest'"

Override a value inside all list items:

<field>.[].<subfield>=<value>

Example:

yaml-patch -f test.yml "spec.template.containers.[].image='mycontainer:latest'"

Append a single value:

<field>.<subfield>+=<value>

Example (increment int):

yaml-patch -f test.yml "spec.replicas+=2"

Example (append string):

yaml-patch -f test.yml "spec.template.containers.[0].image+=':latest'"

Example (append item to list):

yaml-patch -f test.yml "spec.template.containers.[0].args+=['--verbose']"

As a Python library

To use yaml-patch as a library just import the function and pass patches as you would in the CLI examples above.

Example:

from yaml_patch import patch_yaml
from textwrap import dedent

def override_list_all_values():
    source_yaml = dedent(
        """\
        some_list:
          - alice
          - bob
        """
    )
    patches = ["some_list.[]='charlie'"]
    expected_yaml = dedent(
        """\
        some_list:
          - charlie
          - charlie
        """
    )
    assert patch_yaml(source_yaml, patches) == expected_yaml