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This is my example YAML file,

# Employee records

Developer:

  Department: IT

  Manager: ABCD

  Floor: 2nd

  Lab: 4

Support:

  Department: General

  Manager: XYZ

  Floor: 1st

  Lab: 1

Martin:

  name: Martin Devloper

  job: Developer

  skills:

    - python

I want to read this yaml file from a particular directory, edit it and then save the edited text on the same yaml file. I got this code from a link somewhere as follows:

import sys

from ruamel.yaml import YAML

inp_fo = open("C:/<Users>/Master 

1TB/source/repos/New_insertdata/PythonApplication3/inp.yaml").read() 

#Read the YAML File



yaml = YAML()

code = yaml.load(inp_fo)

sys.stdout.write('n')

code.insert(1, 'sensor', 'None', comment="new key")

inp_fo2 = open("inp.yaml","w") #Open the file for Write

yaml.dump(code, inp_fo2) ##Write to file with new parameter

inp_fo2.close() ## close the file

When I execute it I get output as follows:

# Employee records

Developer:

  Department: IT

  Manager: ABCD

  Floor: 2nd

  Lab: 4

Support:

  Department: General

  Manager: XYZ

  Floor: 1st

  Lab: 1

Martin:

  name: Martin 

  job: Developer

  skills:

    - python

Tabitha: None 

But instead I need:

# Employee records

Developer:

  Department: IT

  Manager: ABCD

  Floor: 2nd

  Lab: 4

Support:

  Department: General

  Manager: XYZ

  Floor: 1st

  Lab: 1

Martin:

  name: Martin 

  job: Developer

  skills:

    - python

Tabitha:

  name: Tabitha Bitumen

  job: Developer

  skills:

    - Java

How to code this?

I entered value for 'Tabitha' as None because code.insert was not getting executed if I don't insert a value for it.

Now, I want to edit this yaml file repeatedly so I want to define a variable for each key value, so everytime once the variable value changes the code will be executed and new key values will be inserted in the existing yaml file. I don't want to delete the earlier contents of YAML file just need to go on adding new contents (key & value) (content will be employee details like name, job, skills).

I am completely new to this coding language so if I am wrong please correct me. Also can anyone explain me what is the use of indent, sequence & mapping in ruamel.yaml and how can I use them in code?

I am a learner and the above example is a random yaml file just an example to learn ruamel.yaml.

Let me explain you what I want exactly,
The following content will remain static.

 # Employee records

Developer:

  Department: IT

  Manager: ABCD

  Floor: 2nd

  Lab: 4

Support:

  Department: General

  Manager: XYZ

  Floor: 1st

  Lab: 1

But the key values (employee details) are going to change. Example I want:
Martin:
name: Martin Devloper
job: Developer
skills:
- python

"Martin" should be a "variableP"

name: "variableQ"

job: "variableR"

skills:

  - "variableS"

similarly if another employee adds his details the code will automatically add another employee details in those variables.
because according to your code, I will have to repeatedly add

code['Tabitha'] = dict(name='Tabitha Bitumen', job='Developer', skills=['Java'])

again and again for other employee data which I don't want, I just want a code where I could define a variable whose value will keep on changing and will edit the same yaml file repeatedly and do not delete the earlier employee details.
There is no limit for list of employees to be get added so I don't want to edit the code again and again.

I basically know C and arduino programming language so looking for a way to define variables in a code which will make my work easy.

The following assumes you are using Python3 (and you should if you are
learning Python), because it uses pathlib that is in the standard
library for Python3. There is a
pathlib2 package that provides that
functionality for Python2.

The example code that you present does a few strange things:

• it is not necessary to read in the content of a file
  (open(...).read()) and then hand that to the .load() method, you
  can directly pass in the file pointer (i.e. the result from just
  doing open(), or you can use the Path object and hand this to
  .load() without even opening the file (as shown below).




• it is unclear why a newline is written to sys.stdout, that really
  has no function in this snippet




• the call code.insert(1, 'sensor', 'None', comment="new key") does put 'sensor' as
  a new key, in position 1 of the dictionary like object code, with the value None
  and the end-of-line comment "new key". (Position counting starts at 0.

If you had really ran that code you would get as output:

# Employee records

Developer:

  Department: IT

  Manager: ABCD

  Floor: 2nd

  Lab: 4

sensor: None  # new key

Support:

  Department: General

  Manager: XYZ

  Floor: 1st

  Lab: 1

Martin:

  name: Martin Devloper

  job: Developer

  skills:

  - python

At the root of your input file is a mapping with keys Developer,
Support and Martin. The values associate with a key can again be a
mapping (as is the case for all your root-level keys), but they can
also be a sequence (as is the value for skills, indicated by dash
(-) or scalar values (string, number, etc). The root of a YAML
document can be a scalar (which is then the only object in the
document), or a sequence. And a sequence has elements that can be
scalars (as your final line python), but those elements can also be
mappings or other sequences.

Mappings are loaded as Python dicts, sequences are loaded as Python
lists. In order to preserve comments (and other information),
ruamel.yaml will create dict- resp. list-like objects when used as
in the example. You would not be able to call code.insert() on a regular
Python dict but you can do so on what you got back (from YAML().load())

If you just want to add a key-value pair at the end of a dict, you don't need to
use .insert, you can just do:

code['Tabitha'] = dict(name='Tabitha Bitumen', job='Developer', skills=['Java'])

If you need to move something to the end of the YAML file, you actually cannot
just update the value using e.g.

code['Support'] = dict(Department='General', Manager='KLM', Floor='1st', Lab=1)

this will get you the key/value in the old position. You would have to do

del code['Support']

first to make it forget this old position.

As indicated ruamel.yaml supports multiple ways on how to read and
write to a file. The with statement as Moralous answer introduced
is already better than explicit opening, reading and closing. You can also use
pathlib.Path like objects with the .load() and .dump() methods:

from pathlib import Path

from ruamel.yaml import YAML



path = Path('inp.yaml')  # I shortened this a bit, as I don't have a C: drive

opath = Path('outp.yaml')



yaml = YAML()

code = yaml.load(path)

code['Tabitha'] = dict(name='Tabitha Bitumen', job='Developer', skills=['Java'])

yaml.dump(code, opath)

which gives:

# Employee records

Developer:

  Department: IT

  Manager: ABCD

  Floor: 2nd

  Lab: 4

Support:

  Department: General

  Manager: XYZ

  Floor: 1st

  Lab: 1

Martin:

  name: Martin Devloper

  job: Developer

  skills:

  - python

Tabitha:

  name: Tabitha Bitumen

  job: Developer

  skills:

  - Java

This is almost what you want, but the default indentation of the YAML output
is 2 positions for both the dict (as you want it to be) and for the
sequence (it is counted to the beginning of your element, not to the
dash).

To get what you want, you need to specify an indent of four for the sequence, and
an offset of two for the dash withing those for spaces. You can do so by inserting,
after the yaml = YAML() line, a line with:

yaml.indent(sequence=4, offset=2)

You can also use your YAML instance itself in a with statement:

import sys

from pathlib import Path

from ruamel.yaml import YAML



path = Path('inp.yaml')  # I shortened this a bit, as I don't have a C: drive

opath = Path('outp.yaml')



with YAML(output=opath) as yaml:

    yaml.indent(sequence=4, offset=2)

    code = yaml.load(path)

    code['Tabitha'] = dict(name='Tabitha Bitumen', job='Developer', skills=['Java'])

    yaml.dump(code)

That will also give you exactly you want:

# Employee records

Developer:

  Department: IT

  Manager: ABCD

  Floor: 2nd

  Lab: 4

Support:

  Department: General

  Manager: XYZ

  Floor: 1st

  Lab: 1

Martin:

  name: Martin Devloper

  job: Developer

  skills:

    - python

Tabitha:

  name: Tabitha Bitumen

  job: Developer

  skills:

    - Java

You tagged your question with PyYAML as well. Please note that with that package
you cannot do the above: your comments in the YAML file will be lost, and
you don't have the kind of fine control over indentation to get the result you
wanted.

The YAML library you're using converts between YAML formatting and Python dictionaries. Therefore you could simple edit the dictionary to add or change a value in the YAML file. For example:

import sys

from ruamel.yaml import YAML

filename = "C:/<Users>/Master/1TB/source/repos/New_insertdata/PythonApplication3/inp.yaml"



yaml = YAML()

with open(filename) as inp_fo:

    code = yaml.load(inp_fo)



    code["Tabitha"] = {

                        "name":"Tabitha Bitman",

                        "job":"Developer",

                        "skills":["Python"]

                      }



with open(filename, "w") as file:

    yaml.dump(code, file) ##Write to file with new parameter

There is no need to close the files as they were opened in "with"
statements

This will update Tabitha's details in the YAML file, assuming that the rest of your code is correct.

You can also parse a variable into the key:value lookup, replacing code["Tabitha"] with code[variable_name].

If you are working with YAML (or JSON) files I also highly recommend looking into and understanding dictionaries in Python.