app.py

import streamlit as st
import langcodes
from requests_html import HTMLSession

st.write("# Language code/tag search")
st.write("Fed up with language tag confusion? Here's your one-stop shop!")
st.write("Try typing your language below! Accepts either codes like `eng`/`en`, or full names like `English`, and we will use the [langcodes](https://github.com/rspeer/langcodes) library to figure out the correct modern BCP-47 code according to [official W3 Guidelines](https://www.w3.org/International/questions/qa-choosing-language-tags)")
# https://huggingface.co/blog/streamlit-spaces
# https://github.com/psf/requests-html
# https://docs.streamlit.io/library/api-reference/write-magic/st.write
langtext = st.text_input("Language Code/Tag Lookup using langcodes", "english").strip()

st.write("* Checking whether the tag is valid. That is, the language, script, territory, and variants (if present) are all tags that have meanings assigned by IANA.")

if langcodes.tag_is_valid(langtext):
  st.write(f"* ...True! '{langtext}' parses meaningfully as a language tag according to IANA.")
else:
  st.write(f"* ...False! '{langtext}' doesn't parse meaningfully as a language tag according to IANA, some of its subcomponents may be invalid or it might be a natural language description.")
    

try:
  lang = langcodes.Language.get(langtext)
#  st.write(f"{lang} is the BCP-47 tag.")
  if "unknown" in lang.display_name().lower():
    st.write(f"* Attempting to lookup the code directly gives us '{lang.display_name()}', attempting to search for it as a natural language string.")
    lang = None
except langcodes.LanguageTagError as e: 
  st.write(f"* Could not lookup code directly, attempting to search for it as a natural language string.")
  lang = None
  


if lang is None:
  try:
    found = langcodes.find(langtext)
    lang = found
    st.write(f"* Natural language search found the following BCP-47 tag: {lang}")
  except LookupError as e:
    st.write("## Result: failure!")
    st.write(f"Unable to look up language code. But all hope is not lost...")
    st.write(f"* You can also try https://r12a.github.io/app-subtags/")
    st.write(f"* Or possibly https://glottolog.org/glottolog?search={langtext}")
    lang = None


def pull_obsolete_codes(iso_code):
  session = HTMLSession() 
  r= session.get(f"https://iso639-3.sil.org/code/{iso_code}")
  # https://www.w3schools.com/cssref/css_selectors.asp
  obsolete_codes = {}
  for found_element in r.html.find(".views-field-nothing", clean=True):
    lines = found_element.text.splitlines()
    for line in lines:
      for obsolete_code_name in ["639-1","639-2/B", "639-2/T", "639-3"]:
        if obsolete_code_name in line and ":" in line:
          code = line.split()[-1]
          obsolete_codes[obsolete_code_name] = code  
  return obsolete_codes


#st.write(f"langcodes found the following tag: {type(found)}") # a Language object
if lang is not None: 
  display = lang.display_name()
  b_variant = lang.to_alpha3(variant='B')
  t_variant = lang.to_alpha3(variant='T')
  broader_tags = lang.broader_tags()
  st.write("## Results")
  st.write(f"Best-match BCP-47 tag for '{langtext}', according to the langcodes library: {lang}")  
  st.write(f"Breakdown of tag components:")  
  st.write(lang.describe())
  st.write(f"Display name for {lang}: {lang.display_name()}")
  st.write(f"Autonym for {lang}: {lang.autonym()}")
  st.write(f"**Correct, standardized, BCP-47 tag for {langtext}, according to the langcodes library:** `{langcodes.standardize_tag(lang)}`")
  
  
  st.write("## Further Information:")

  st.write(f"Broader tags for this language, if any:")
  st.write(broader_tags)
  st.write(f"Try also: https://r12a.github.io/app-subtags/?lookup={lang}")
  st.write(f"https://glottolog.org/glottolog?search={t_variant} may be of interest, with links to Ethnologue, etc. If that doesn't work, try https://glottolog.org/glottolog?search={b_variant}")  

  # ethnologue prefers T for german (deu), and T for French
  st.write("## Older Codes")

  st.write(f"ISO 639-3 'alpha3' code, 'terminology' variant (deprecated): {t_variant}")
  st.write(f"ISO 639-3 'alpha3' code, 'bibliographic' variant (deprecated): {b_variant}")
  st.write(f"If it exists, the ISO 639 Code Tables entry for the T variant would be at https://iso639-3.sil.org/code/{t_variant}")
  st.write(f"If it exists, the ISO 639 Code Tables entry for the B variant would be at https://iso639-3.sil.org/code/{b_variant}")  
  obsolete_codes = pull_obsolete_codes(t_variant)
  
  #TODO: Cleanup this bit
  if obsolete_codes:
    st.write(f"Obsolete codes from previous ISO-639 iterations, pulled from https://iso639-3.sil.org/code/{t_variant}:")
    st.write(obsolete_codes)
  else:
    obsolete_codes = pull_obsolete_codes(b_variant)      
    if obsolete_codes:
      st.write(f"Obsolete codes from previous ISO-639 iterations, pulled from https://iso639-3.sil.org/code/{b_variant}:")

      st.write(obsolete_codes)