NAME

kera — Fill template files with structured data

SYNOPSIS

kera plate_files... data_files...

OPTIONS

-o, --out-dir : The directory in which to write all files. Defaults to the current directory.

INSTALL

kera can be installed using the pip package manager, where it is available under the name kera.

To install just the executable command line interface, I would use pipx:

pipx install kera

To install it as a library, use pip and a venv.

DESCRIPTION

This program takes a collection of template files, a collection of data files, and then uses the data to fill placeholder "slots" in the templates. Each individual data file produces an output for each individual template file.

To represent a simple slot in a template file, surround it in double hashes:

= ##title##
by ##name## on ##date##

##content##

And provide the data in your format of choice:

{
    "title": "kera",
    "name": "C Wiebe",
    "date": "JAN 01 1970",
    "content": "Fill template files with structured data."
}

This results in:

= kera
by C Wiebe on JAN 01 1970

Fill template files with structured data.

GLOSSARY

plate file : A file containing a template; optionally can have the extension .plate

data file : A file containing structured data; can be either a JSON file or a YAML file

slot : A string in a plate file that will be replaced with data from a data file

key : The identifier used to select which value from a data file is used to fill any given slot; the key in a key / value pair

conditional slot : A slot that has a condition attached to it

collection slot : A slot whose key points to a collection of nested data

AS AN EXECUTABLE

The executable version of kera has the name kera and takes any number of filenames as its arguments.

Template files can have the extension .plate, but any file that isn't a data file will be read as a template by default. Supported data filetypes are:

• JSON
• YAML

If you want to use a data file as a template file, it must have the .plate extension, e.g. .json.plate.

The default filename of the filled template is the name of the data file (minus extension), an underscore, and the name of the template file (with extension, minus .plate if present). These output files can be redirected to a different directory with the --out option.

As an example:

$ ls
> 123.sql 456.sql.plate abc.json def.yml
$ kera --out output 123.sql 456.sql.plate abc.json def.yml
$ ls output
> abc_123.sql abc_456.sql def_123.sql def_456.sql

AS A LIBRARY

The library version of kera has the name kera and provides one function:

process(plate: str, data: dict[str, any]) -> str

This function takes a plate (a string containing the template text whose slots will be filled) and a data (a dictionary containing the key / value pairs that will be used to populate the template). The function will fill all the template slots using the data and then returns the populated template string.

As a simple example:

import kera

plate = "Hello, ##name##!"
data = {
    "name": "World",
}

result = kera.process(plate, data)
print(result)
#> Hello, World!

CONDITIONAL SLOTS

kera supports additional types of slots that introduce additional functionality. Conditional slots (analogous to if statements) can be represented as such:

##[ condition ]{{ if true }}{{ if false (optional) }}

The condition is simply a key found in the data, and it is true if the value of the key is truthy according to Python. If the key is not found, it is automatically false. The "body" of the conditional slot is treated the same as the rest of the text; you can include other slots inside it and nest slots as much as you wish.

An example of conditional slots in use:

<div class="profile">
    <h3>##name##</h3>
    <ul class="inline">
        ##[pronouns]{{ <li>##pronouns##</li> }}
        ##[language]{{ <li>##language##</li> }}
        ##[join-date]{{ <li>Joined ##join-date##</li> }}
    </ul>
    ##[desc]{{
        ##desc##
    }}{{
        <p>No bio provided.</p>
    }}
</div>

With this, you can process both full profiles:

name: Scofflaw Saxwulf
pronouns: he/him
language: ENG | FIN
join-date: AUG 23 2025
desc: <p>INSERT INTERESTING BIO HERE</p>

<div class="profile">
    <h3>Scofflaw Saxwulf</h3>
    <ul class="inline">
        <li>he/him</li>
        <li>ENG | FIN</li>
        <li>Joined AUG 23 2025</li>
    </ul>
    <p>INSERT INTERESTING BIO HERE</p>
</div>

And partial profiles:

name: Lusaka Hernesto
pronouns: she/her

<div class="profile">
    <h3>Lusaka Hernesto</h3>
    <ul class="inline">
        <li>she/her</li>
        
        
    </ul>
    <p>No bio provided.</p>
</div>

COLLECTION SLOTS

Collection slots (analogous to for loops) are represented as:

##collection{{ body for each collection member }}

In a collection body, the "scope" that contains available keys now includes the keys nested within the collection key (when names conflict, the child keys override the parent keys). This is easier shown than explained:

table: Person
joins:
  - table: Place
    alias: a
    join-on: addressId

  - table: Place
    alias: w
    join-on: workAddressId

  - table: Job
    alias: j
    join-on: workId

SELECT  *
FROM    ##table##
     -- ^ Table in the parent scope
##joins{{
JOIN    ##table## ##alias## ON ##join-on## = ##alias##.id
     -- ^ Table in the child scope overrides parent scope
}};

SELECT  *
FROM    Person
     -- ^ Table in the parent scope
JOIN    Place a ON addressId = a.id
     -- ^ Table in the child scope overrides parent scope
JOIN    Place w ON workAddressId = w.id
     -- ^ Table in the child scope overrides parent scope
JOIN    Job j ON workId = j.id
     -- ^ Table in the child scope overrides parent scope;

By default each member of the collection is joined with a newline, but you can alter this by providing a join string before the collection body that is surrounded by parenthesis:

table: Record
columns:
  - name: create_date
    type: DATE

  - name: update_date
    type: DATE

  - name: id
    type: INTEGER

  - name: content
    type: TEXT

CREATE PROCEDURE insert_into_##table##
( ##columns(\n, ){{
    p_##name## IN ##type##
  }}
)
BEGIN

    INSERT
    INTO    ##table##
            ( ##columns(\n            , ){{
                ##name##
              }}
            )
    VALUES  ( ##columns(\n            , ){{
                p_##name##
              }}
            );

END insert_into_##table##;

CREATE PROCEDURE insert_into_Record
( p_create_date IN DATE
, p_update_date IN DATE
, p_id IN INTEGER
, p_content IN TEXT
)
BEGIN

    INSERT
    INTO    Record
            ( create_date
            , update_date
            , id
            , content
            )
    VALUES  ( p_create_date
            , p_update_date
            , p_id
            , p_content
            );

END insert_into_Record;

APPENDIX

ACCESSING NESTED VALUES

Say you have a nested object like so:

{
    "parent": {
        "child": "value"
    }
}

In these instances, the values within the nested object can be accessed using dot notation, e.g. ##parent.child##.

OVERRIDING DEFAULT NAMES

The default name of an output file produced by the executable can be overriden by including the key _out_file in the data file, where the value of _out_file is the name of the resulting file. If that data file is used with multiple plate files, it will result in the same name each time.

RETURN CODES

0 : Code execution was successful.

1 : Unable to create or find the given output directory.

BUGS

1. If a key in YAML is made up of numbers and only numbers, the YAML parser will store it as an integer, which won't be resolved properly when kera tries to retrieve it as a string. To prevent this, surround such keys with double quotes:

   # bad:
   1: this won't be resolved
   # good:
   "1": this WILL be resolved
   

SEE ALSO

• Source code
• Online README
• CHANGELOG