How to update yaml file using python

Question

I have a some.yaml file with the below contents.

    init_config: {}     instances:         - host: <IP>           username: <username>           password: <password> 

The yaml file should be parsed and updated as below.

    init_config: {}     instances:         - host: 1.2.3.4           username: Username           password: Password 

How do I parse the values and update them appropriately?

Answer 1

The ruamel.yaml package was specifically enhanced (by me starting from PyYAML) to do this kind of round-trip, programmatic, updating.

If you start with (please note I removed the extra initial spaces):

init_config: {} instances:     - host: <IP>              # update with IP       username: <username>    # update with user name       password: <password>    # update with password 

and run:

import ruamel.yaml  file_name = 'input.yaml' config, ind, bsi = ruamel.yaml.util.load_yaml_guess_indent(open(file_name))  instances = config['instances'] instances[0]['host'] = '1.2.3.4' instances[0]['username'] = 'Username' instances[0]['password'] = 'Password'  yaml = ruamel.yaml.YAML() yaml.indent(mapping=ind, sequence=ind, offset=bsi)  with open('output.yaml', 'w') as fp:     yaml.dump(config, fp) 

The output will be:

init_config: {} instances:     - host: 1.2.3.4           # update with IP       username: Username      # update with user name       password: Password      # update with password 

The ordering of mapping keys (host, username and password), the style and the comments are preserved without any further specific action.

Instead of having the indent and block sequence indent guessed, you can do a manual traditional load, and set the indent values yourself:

yaml = ruamel.yaml.YAML() yaml.indent(mapping=6, sequence=4) with open(file_name) as fp:     config = yaml.load(fp) 

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If you look at the history of this answer, you can see how to do this with a more limited, PyYAML like, API.

Answer 2

This is how i can read from the above file i mentioned, parse and update as needed.

import yaml  fname = "some.yaml"  stream = open(fname, 'r') data = yaml.load(stream)  data['instances'][0]['host'] = '1.2.3.4' data['instances'][0]['username'] = 'Username' data['instances'][0]['password'] = 'Password'  with open(fname, 'w') as yaml_file:     yaml_file.write( yaml.dump(data, default_flow_style=False))