pftag

A string template processor: %{tags} in text are resolved when the text is used, each optionally piped through functions. Both a library and a command.

Overview

A template is ordinary text with tags in it. A tag is %{, a name, optional functions, }:

run-%{timestamp}-on-%{hostname}.log
%{inputWorkingFile|rmext}.jpg
%{timestamp|replace(:,-)|md5(6)}
%{"Subject12345"|sha256(8)}

Names resolve against the core tags (timestamp, date, hostname, platform, user, pid) and against dictionaries the calling program registers. Functions read left to right, each feeding the next; text after the closing } is kept. Nothing outside %{...} is a tag, so printf "%s", date +%Y%m%d and %20 in a URL pass through untouched. An unknown name is left as written unless --strict.

The full reference is docs/tags.adoc. The pf* family uses pftag wherever a user writes a template on the command line: pfdo_run's --exec string, pflog's telemetry URLs.

Installation

pip install pftag            # no dependencies
pip install 'pftag[names]'   # adds faker, for the dcmname pseudonym function

Python 3.11 or newer.

Command

pftag --tag "run-%{timestamp}-on-%{hostname}.log"
pftag --tag "run-%{timestamp|replace(:,-)|md5(6)}.log"
pftag --tag "run-%{timestamp|strftime(%Y%m%d-%H%M)}.log"
pftag --lookupDictAdd '{"s": {"user": "chris"}}' --tag "user %{user}, hash %{user|md5(8)}"
pftag --tag "%{nope}" --strict        # exit 1: unknown tag
pftag --tag "..." --json              # the whole result: tags found, unknown, legacy, functions applied, errors
pftag --man

Library

import shlex
from pftag import Pftag, TagOptions

tagger = Pftag(TagOptions(lookups={"run": {"subject": "sub-01", "file": "T1.nii.gz"}}))
tagger("%{subject}/%{file|rmext}.jpg").result  # 'sub-01/T1.nii.jpg'
tagger.argv_process(shlex.split("convert %{file} %{file|rmext}.jpg")).argv

process(template) is for text; argv_process(argv) is for commands: split the user's command first, then each argument is a template of its own, so a value with a space or a quote cannot change the shape of the command. lookup_add(name, values) registers a dictionary; a FunctionRegistry passed to Pftag takes new functions with add(name, fn), where fn(value, args) -> str.

Functions

Changes in 3.0

• Tags are %{...} only. The bare %name form is gone; a bare % is always literal. A bare %name of a known name is reported as a 1.x tag (and fails under --strict) so that old templates do not pass through silently.
• Functions are |fn(arg, arg) in pipe order; arguments bare or quoted; fn or fn(). A quoted head starts a chain from literal text, replacing %literal and echo.
• Names may contain underscores; %{dict.name} qualifies; two dictionaries defining one name is an error at registration.
• argv_process for commands. Values are substituted once, never re-processed.
• Functions renamed to common names: replace, re, mask; ext, basename, dirname, strip, pad, slice, sha256, strftime added; chrplc, strrepl, strmsk, echo gone. dcmname moves behind the names extra and seeds its own generator.
• Core tags: timestamp, date, hostname, platform, user, pid; os, release, machine, arch, literal gone.
• No configurable markers, no dependencies, no pudb/loguru/XDG_CONFIG_HOME side effects; pyproject.toml only, CI on 3.11–3.14 and 3.14t, published from a v* tag; the Docker image is no longer built.