Examples

JSON to NestedText

This example implements a command-line utility that converts a JSON file to NestedText. It demonstrates the use of dumps() and NestedTextError.

#!/usr/bin/env python3
"""
Read a JSON file and convert it to NestedText.

usage:
    json-to-nestedtext [options] [<filename>]

options:
    -f, --force            force overwrite of output file
    -i <n>, --indent <n>   number of spaces per indent [default: 4]
    -s, --sort             sort the keys
    -w <n>, --width <n>    desired maximum line width; specifying enables
                           use of single-line lists and dictionaries as long
                           as the fit in given width [default: 0]

If <filename> is not given, JSON input is taken from stdin and NestedText output 
is written to stdout.
"""

from docopt import docopt
from inform import done, fatal, full_stop, os_error, warn
from pathlib import Path
import json
import nestedtext as nt
import sys
sys.stdin.reconfigure(encoding='utf-8')
sys.stdout.reconfigure(encoding='utf-8')

cmdline = docopt(__doc__)
input_filename = cmdline['<filename>']
try:
    indent = int(cmdline['--indent'])
except Exception:
    warn('expected positive integer for indent.', culprit=cmdline['--indent'])
    indent = 4
try:
    width = int(cmdline['--width'])
except Exception:
    warn('expected non-negative integer for width.', culprit=cmdline['--width'])
    width = 0

try:
    # read JSON content; from file or from stdin
    if input_filename:
        input_path = Path(input_filename)
        json_content = input_path.read_text(encoding='utf-8')
    else:
        json_content = sys.stdin.read()
    data = json.loads(json_content)

    # convert to NestedText
    nestedtext_content = nt.dumps(
        data,
        indent = indent,
        width = width,
        sort_keys = cmdline['--sort']
    )

    # output NestedText content; to file or to stdout
    if input_filename:
        output_path = input_path.with_suffix('.nt')
        if output_path.exists():
            if not cmdline['--force']:
                fatal('file exists, use -f to force over-write.', culprit=output_path)
        output_path.write_text(nestedtext_content, encoding='utf-8')
    else:
        sys.stdout.write(nestedtext_content + "\n")

except OSError as e:
    fatal(os_error(e))
except nt.NestedTextError as e:
    e.terminate()
except UnicodeError as e:
    fatal(full_stop(e))
except KeyboardInterrupt:
    done()
except json.JSONDecodeError as e:
    # create a nice error message with surrounding context
    msg = e.msg
    culprit = input_filename
    codicil = None
    try:
        lineno = e.lineno
        culprit = (culprit, lineno)
        colno = e.colno
        lines_before = e.doc.split('\n')[max(lineno-2, 0):lineno]
        lines = []
        for i, l in zip(range(lineno-len(lines_before), lineno), lines_before):
            lines.append(f'{i+1:>4}> {l}')
        lines_before = '\n'.join(lines)
        lines_after = e.doc.split('\n')[lineno:lineno+1]
        lines = []
        for i, l in zip(range(lineno, lineno + len(lines_after)), lines_after):
            lines.append(f'{i+1:>4}> {l}')
        lines_after = '\n'.join(lines)
        codicil = f"{lines_before}\n     {colno*' '}▲\n{lines_after}"
    except Exception:
        pass
    fatal(full_stop(msg), culprit=culprit, codicil=codicil)

Be aware that not all JSON data can be converted to NestedText, and in the conversion much of the type information is lost.

json-to-nestedtext can be used as a JSON pretty printer:

> json-to-nestedtext < fumiko.json
treasurer:
    name: Fumiko Purvis
    address:
        > 3636 Buffalo Ave
        > Topeka, Kansas 20692
    phone: 1-268-555-0280
    email: fumiko.purvis@hotmail.com
    additional roles:
        - accounting task force

NestedText to JSON

This example implements a command-line utility that converts a NestedText file to JSON. It demonstrates the use of load() and NestedTextError.

#!/usr/bin/env python3
"""
Read a NestedText file and convert it to JSON.

usage:
    nestedtext-to-json [options] [<filename>]

options:
    -f, --force   force overwrite of output file
    -d, --dedup   de-duplicate keys in dictionaries

If <filename> is not given, NestedText input is taken from stdin and JSON output 
is written to stdout.
"""

from docopt import docopt
from inform import done, fatal, os_error, full_stop
from pathlib import Path
import json
import nestedtext as nt
import sys
sys.stdin.reconfigure(encoding='utf-8')
sys.stdout.reconfigure(encoding='utf-8')


def de_dup(key, state):
    if key not in state:
        state[key] = 1
    state[key] += 1
    return f"{key} — #{state[key]}"


cmdline = docopt(__doc__)
input_filename = cmdline['<filename>']
on_dup = de_dup if cmdline['--dedup'] else None

try:
    if input_filename:
        input_path = Path(input_filename)
        data = nt.load(input_path, top='any', on_dup=on_dup)
        json_content = json.dumps(data, indent=4, ensure_ascii=False)
        output_path = input_path.with_suffix('.json')
        if output_path.exists():
            if not cmdline['--force']:
                fatal('file exists, use -f to force over-write.', culprit=output_path)
        output_path.write_text(json_content, encoding='utf-8')
    else:
        data = nt.load(sys.stdin, top='any', on_dup=on_dup)
        json_content = json.dumps(data, indent=4, ensure_ascii=False)
        sys.stdout.write(json_content + '\n')
except OSError as e:
    fatal(os_error(e))
except nt.NestedTextError as e:
    e.terminate()
except UnicodeError as e:
    fatal(full_stop(e))
except KeyboardInterrupt:
    done()

PyTest

This example highlights a PyTest package parametrize_from_file that allows you to neatly separate your test code from your test cases; the test cases being held in a NestedText file. Since test cases often contain code snippets, the ability of NestedText to hold arbitrary strings without the need for quoting or escaping results in very clean and simple test case specifications. Also, use of the eval function in the test code allows the fields in the test cases to be literal Python code.

The test cases:

# test_expr.nt
test_substitution:
  -
    given:   first  second
    search: ^\s*(\w+)\s*(\w+)\s*$
    replace: \2 \1
    expected: second first
  -
    given: 4 * 7
    search: ^\s*(\d+)\s*([-+*/])\s*(\d+)\s*$
    replace: \1 \3 \2
    expected: 4 7 *

test_expression:
  -
    given: 1 + 2
    expected: 3
  -
    given: "1" + "2"
    expected: "12"
  -
    given: pathlib.Path("/") / "tmp"
    expected: pathlib.Path("/tmp")

And the corresponding test code:

# test_misc.py
import parametrize_from_file
import re
import pathlib

@parametrize_from_file
def test_substitution(given, search, replace, expected):
    assert re.sub(search, replace, given) == expected

@parametrize_from_file
def test_expression(given, expected):
    assert eval(given) == eval(expected)

PostMortem

PostMortem is a program that generates a packet of information that is securely shared with your dependents in case of your death. Only the settings processing part of the package is shown here.

This example includes references, key normalization, and different way to implement validation and conversion on a per field basis with voluptuous. References allow you to define some content once and insert that content multiple places in the document. Key normalization allows the keys to be case insensitive and contain white space even though the program that uses the data prefers the keys to be lower case identifiers.

Here is a configuration file that Odin might use to generate packets for his wife and kids:

my GPG ids: odin@norse-gods.com
sign with: @ my gpg ids
name template: {name}-{now:YYMMDD}
estate docs:
    - ~/home/estate/trust.pdf
    - ~/home/estate/will.pdf
    - ~/home/estate/deed-valhalla.pdf

recipients:
    Frigg:
        email: frigg@norse-gods.com
        category: wife
        attach: @ estate docs
        networth: odin
    Thor:
        email: thor@norse-gods.com
        category: kids
        attach: @ estate docs
    Loki:
        email: loki@norse-gods.com
        category: kids
        attach: @ estate docs

Notice that estate docs is defined at the top level. It is not a PostMortem setting; it simply defines a value that will be interpolated into settings later. The interpolation is done by specifying @ along with the name of the reference as a value. So for example, in recipients attach is specified as @ estate docs. This causes the list of estate documents to be used as attachments. The same thing is done in sign with, which interpolates my gpg ids.

Here is the code for validating and transforming the PostMortem settings. For more on report_voluptuous_errors, see Validate with Voluptuous.

#!/usr/bin/env python3

from inform import error, os_error, terminate
import nestedtext as nt
from pathlib import Path
from voluptuous import (
    Schema, Invalid, MultipleInvalid, Extra, Required, REMOVE_EXTRA
)
from voluptuous_errors import report_voluptuous_errors
from pprint import pprint

# Settings schema
# First define some functions that are used for validation and coercion
def to_str(arg):
    if isinstance(arg, str):
        return arg
    raise Invalid(f"expected text, found {arg.__class__.__name__}")

def to_ident(arg):
    arg = to_str(arg)
    if arg.isidentifier():
        return arg
    raise Invalid('expected simple identifier')

def to_list(arg):
    if isinstance(arg, str):
        return arg.split()
    if isinstance(arg, dict):
        raise Invalid(f"expected list, found {arg.__class__.__name__}")
    return arg

def to_paths(arg):
    return [Path(p).expanduser() for p in to_list(arg)]

def to_email(arg):
    email = to_str(arg)
    user, _, host = email.partition('@')
    if '.' in host and '@' not in host:
        return arg
    raise Invalid('expected email address')

def to_emails(arg):
    return [to_email(e) for e in to_list(arg)]

def to_gpg_id(arg):
    try:
        return to_email(arg)      # gpg ID may be an email address
    except Invalid:
        try:
            int(arg, base=16)     # if not an email, it must be a hex key
            assert len(arg) >= 8  # at least 8 characters long
            return arg
        except (ValueError, TypeError, AssertionError):
            raise Invalid('expected GPG id')

def to_gpg_ids(arg):
    return [to_gpg_id(i) for i in to_list(arg)]

def to_snake_case(key):
    return '_'.join(key.strip().lower().split())

# provide user-friendly error messages
voluptuous_error_msg_mappings = {
    "extra keys not allowed": ("unknown key", "key"),
    "expected a dictionary": ("expected key-value pairs", "value"),
}

# define the schema for the settings file
schema = Schema(
    {
        Required('my_gpg_ids'): to_gpg_ids,
        'sign_with': to_gpg_id,
        'avendesora_gpg_passphrase_account': to_str,
        'avendesora_gpg_passphrase_field': to_str,
        'name_template': to_str,
        Required('recipients'): {
            Extra: {
                Required('category'): to_ident,
                Required('email'): to_emails,
                'gpg_id': to_gpg_id,
                'attach': to_paths,
                'networth': to_ident,
            }
        },
    },
    extra = REMOVE_EXTRA
)

# this function implements references
def expand_settings(value):
    # allows macro values to be defined as a top-level setting.
    # allows macro reference to be found anywhere.
    if isinstance(value, str):
        value = value.strip()
        if value[:1] == '@':
            value = settings.get(to_snake_case(value[1:]))
        return value
    if isinstance(value, dict):
        return {k:expand_settings(v) for k, v in value.items()}
    if isinstance(value, list):
        return [expand_settings(v) for v in value]
    raise NotImplementedError(value)

def normalize_key(key, parent_keys):
    if parent_keys != ('recipients',):
        # normalize all keys except the recipient names
        return to_snake_case(key)
    return key

try:
    # Read settings
    config_filepath = Path('postmortem.nt')
    if config_filepath.exists():

        # load from file
        settings = nt.load(
            config_filepath,
            keymap = (keymap:={}),
            normalize_key = normalize_key
        )

        # expand references
        settings = expand_settings(settings)

        # check settings and transform to desired types
        settings = schema(settings)

        # show the resulting settings
        print(nt.dumps(settings, default=str))

except nt.NestedTextError as e:
    e.report()
except MultipleInvalid as e:
    report_voluptuous_errors(e, keymap, config_filepath)
except OSError as e:
    error(os_error(e))
terminate()

This code uses expand_settings to implement references, and it uses the Voluptuous schema to clean and validate the settings and convert them to convenient forms. For example, the user could specify attach as a string or a list, and the members could use a leading ~ to signify a home directory. Applying to_paths in the schema converts whatever is specified to a list and converts each member to a pathlib path with the ~ properly expanded.

Notice that the schema is defined in a different manner than in the :ref:` Volupuous example <voluptuous example>`. In that example, you simply state which type you are expecting for the value and you use the Coerce function to indicate that the value should be cast to that type if needed. In this example, simple functions are passed in that perform validation and coercion as needed. This is a more flexible approach that allows better control of the conversions and the error messages.

This code does not do any thing useful, it just reads in and expands the information contained in the input file. It simply represents the beginnings of a program that would use the specified information to generate the postmortem reports. In this case it simply prints the expanded information in the form of a NestedText document, which is easier to read that if it were pretty-printed as Python or JSON.

Here are the processed settings:

my_gpg_ids:
    - odin@norse-gods.com
sign_with: odin@norse-gods.com
name_template: {name}-{now:YYMMDD}
recipients:
    Frigg:
        email:
            - frigg@norse-gods.com
        category: wife
        attach:
            - ~/home/estate/trust.pdf
            - ~/home/estate/will.pdf
            - ~/home/estate/deed-valhalla.pdf
        networth: odin
    Thor:
        email:
            - thor@norse-gods.com
        category: kids
        attach:
            - ~/home/estate/trust.pdf
            - ~/home/estate/will.pdf
            - ~/home/estate/deed-valhalla.pdf
    Loki:
        email:
            - loki@norse-gods.com
        category: kids
        attach:
            - ~/home/estate/trust.pdf
            - ~/home/estate/will.pdf
            - ~/home/estate/deed-valhalla.pdf