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demo_bert / src /streamlit_app.py

Update src/streamlit_app.py

af794b4 verified 9 months ago

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import streamlit as st
import torch
import numpy as np
import pandas as pd
from transformers import AutoTokenizer, AutoModel, pipeline
from typing import Optional, Tuple, Dict, Any, List
import json

try:
    from sklearn.decomposition import PCA
except ImportError:
    PCA = None
try:
    import plotly.express as px
except ImportError:
    px = None

st.set_page_config(page_title="BERT – Tokenizer & Embeddings Demo", layout="wide")

st.title("BERT – Architecture, Tokenizer, ID↔Token, Fill-Mask, Embeddings, PCA Map")

# -----------------------------
# Helpers
# -----------------------------

def _device() -> torch.device:
    return torch.device("cuda" if torch.cuda.is_available() else "cpu")


def count_params(model: torch.nn.Module) -> Tuple[int, int]:
    total = sum(p.numel() for p in model.parameters())
    trainable = sum(p.numel() for p in model.parameters() if p.requires_grad)
    return total, trainable


def safe_json(obj: Any) -> str:
    try:
        return json.dumps(obj, indent=2, ensure_ascii=False, default=str)
    except Exception:
        return str(obj)
    
# ----------------------------
# Sidebar: model selection
# ----------------------------

st.sidebar.header("⚙️ Settings")
model_name = st.sidebar.text_input("Hugging Face model name", value="google-bert/bert-base-uncased")
use_hidden_states = st.sidebar.checkbox("output_hidden_states", value=False)
max_vocab_rows = st.sidebar.slider("Rows per page (vocab viewer)", 50, 2000, 500, step=50)

device = _device()
st.sidebar.write("Device:", str(device))


@st.cache_resource(show_spinner=False)
def load_tokenizer_and_model(model_name: str, output_hidden_states: bool):
    tok = AutoTokenizer.from_pretrained(model_name, use_fast=True)
    mdl = AutoModel.from_pretrained(model_name, output_hidden_states=output_hidden_states)
    mdl.eval()
    return tok, mdl


@st.cache_resource(show_spinner=False)
def load_fill_mask(model_name: str):
    # fill-mask uses AutoModelForMaskedLM under the hood when you pass model id
    return pipeline("fill-mask", model=model_name)


with st.spinner("Loading tokenizer + model…"):
    tokenizer, model = load_tokenizer_and_model(model_name, use_hidden_states)
model = model.to(device)

# ----------------------------
# "Tabs" controlled via session_state
# (workaround so the active section does not reset to the first one)
# ----------------------------
TAB_LABELS = [
    "Architecture",
    "Tokenizer vocab",
    "ID ↔ Token",
    "Fill-mask",
    "Embeddings output",
    "Embeddings map",  
]

if "active_tab" not in st.session_state:
    st.session_state["active_tab"] = TAB_LABELS[0]

active_tab = st.radio(
    "Section",
    TAB_LABELS,
    index=TAB_LABELS.index(st.session_state["active_tab"]),
    horizontal=True,
    key="main_tab_selector",
)
st.session_state["active_tab"] = active_tab

# ----------------------------
# Architecture tab
# ----------------------------

if active_tab == "Architecture":
    col1, col2 = st.columns([1, 1])

    with col1:
        st.subheader("Infos générales")
        total, trainable = count_params(model)
        st.write(
            {
                "model_id": model_name,
                "model_class": model.__class__.__name__,
                "total_params": total,
                "trainable_params": trainable,
                "dtype": str(next(model.parameters()).dtype),
                "device": str(next(model.parameters()).device),
            }
        )

        st.subheader("model.eval()")
        st.write("✅ Le modèle est en mode évaluation (`eval()`).")

        st.subheader("config (model.config)")
        try:
            cfg = model.config.to_dict()
        except Exception:
            cfg = vars(model.config)
        st.code(safe_json(cfg), language="json")

    with col2:
        st.subheader("Architecture (str(model))")
        # éviter d'afficher 5000 lignes
        model_str = str(model)
        if len(model_str) > 12000:
            model_str = model_str[:12000] + "\n...\n[tronqué]"
        st.code(model_str)

        st.subheader("Couche d’input embeddings")
        try:
            emb_layer = model.get_input_embeddings()
            w = emb_layer.weight
            st.write(
                {
                    "embedding_weight_shape": list(w.shape),
                    "vocab_size (weight)": int(w.shape[0]),
                    "hidden_dim": int(w.shape[1]),
                }
            )
        except Exception as e:
            st.warning(f"Impossible d’accéder à get_input_embeddings(): {e}")

# ----------------------------
# 1) Tokenizer vocab
# ----------------------------
if active_tab == "Tokenizer vocab":
    st.subheader("Tokenizer vocabulary")
    st.write({"len(tokenizer)": len(tokenizer), "model": model_name})

    # Efficient vocab browsing: build only the requested slice
    total = len(tokenizer)
    if total == 0:
        st.warning("Tokenizer vocabulary appears empty.")
    else:
        # page slider on ID range
        max_start = max(total - max_vocab_rows, 0)
        start = st.slider("Start ID", 0, max_start, min(1000, max_start), step=max_vocab_rows)
        end = min(start + max_vocab_rows, total)

        ids = list(range(start, end))
        # decode single id -> token string (close to your original)
        tokens = [tokenizer.decode(i) for i in ids]

        df = pd.DataFrame({"ID": ids, "token": tokens})
        st.dataframe(df, use_container_width=True, height=520)

        with st.expander("Special tokens"):
            st.write("special_tokens_map:", tokenizer.special_tokens_map)
            st.write("all_special_tokens:", getattr(tokenizer, "all_special_tokens", []))
            st.write("all_special_ids:", getattr(tokenizer, "all_special_ids", []))

# ----------------------------
# 2) ID ↔ Token conversion
# ----------------------------
if active_tab == "ID ↔ Token":
    st.subheader("Convert text → ids/tokens and ids → text")

    text = st.text_area(
        "Text to tokenize",
        value="Sustainable thermal insulation biocomposites from rice husk",
        height=100,
    )

    enc = tokenizer(text, return_tensors="pt")
    ids = enc["input_ids"][0].tolist()
    toks = tokenizer.convert_ids_to_tokens(ids)
    decoded_list = tokenizer.decode(ids, skip_special_tokens=False)
    decoded_clean = tokenizer.decode(ids, skip_special_tokens=True)

    c1, c2 = st.columns(2)
    with c1:
        st.markdown("**input_ids**")
        st.code(ids)
        st.markdown("**tokens**")
        st.code(toks)
    with c2:
        st.markdown("**decode(ids) (keep specials)**")
        st.code(decoded_list)
        st.markdown("**decode(ids) (skip specials)**")
        st.code(decoded_clean)

    st.divider()
    st.subheader("Single conversions")
    cc1, cc2 = st.columns(2)

    with cc1:
        st.markdown("**ID → token**")
        id_in = st.number_input("ID", min_value=0, max_value=max(len(tokenizer) - 1, 0), value=min(101, max(len(tokenizer) - 1, 0)))
        # decode([id]) gives the string form for that single id
        st.write({"id": int(id_in), "token": tokenizer.decode([int(id_in)])})

    with cc2:
        st.markdown("**token → ID**")
        tok_in = st.text_input("Token (as in vocab, e.g. 'insulation' or '##ing')", value="insulation")
        if tok_in:
            st.write({"token": tok_in, "id": int(tokenizer.convert_tokens_to_ids(tok_in))})

# ----------------------------
# 3) Embeddings output
# ----------------------------
if active_tab == "Embeddings output":
    st.subheader("Model forward → last_hidden_state")

    text2 = st.text_area(
        "Text for embeddings",
        value="Sustainable thermal insulation biocomposites from rice husk",
        height=90,
    )

    inputs = tokenizer(text2, return_tensors="pt").to(device)
    with torch.no_grad():
        outputs = model(**inputs)

    last_hidden = getattr(outputs, "last_hidden_state", None)
    if last_hidden is None:
        st.warning("This model output has no last_hidden_state (unexpected for AutoModel). Try another model.")
    else:
        toks = tokenizer.convert_ids_to_tokens(inputs["input_ids"][0].tolist())
        emb = last_hidden[0].detach().cpu().numpy()  # (seq_len, hidden_dim)

        df = pd.DataFrame(
            emb,
            index=[f"{i} {t}" for i, t in enumerate(toks)],
            columns=[f"d{j}" for j in range(emb.shape[1])],
        )
        st.dataframe(df, use_container_width=True, height=520)

# ----------------------------
# 4) Embeddings map (multi-sentence)
# ----------------------------
if active_tab == "Embeddings map":
    st.subheader("Multi-sentence embeddings → PCA map")
    st.write("Enter several sentences (one per line). Embeddings are computed and projected to 2D for visualization.")

    default_sentences = "Sustainable thermal insulation biocomposites.\nRice husk and natural fibers.\nEnergy-efficient building materials.\nRecycled plastic composites.\nWood fiber insulation."
    sentences_text = st.text_area("Sentences (one per line)", value=default_sentences, height=120, key="embed_map_sentences")

    level = st.radio("Embedding level", ["Token level", "Sentence level"], horizontal=True, key="embed_map_level")

    if st.button("Compute embeddings and plot", type="primary", key="embed_map_btn"):
        lines = [s.strip() for s in sentences_text.strip().split("\n") if s.strip()]
        if not lines:
            st.warning("Enter at least one sentence.")
        elif PCA is None:
            st.error("scikit-learn is required for PCA. Install it with `pip install scikit-learn`.")
        elif px is None:
            st.error("plotly is required. Install it with `pip install plotly`.")
        else:
            with st.spinner("Computing embeddings…"):
                all_embeddings: List[np.ndarray] = []
                all_labels: List[str] = []

                for sent in lines:
                    inputs = tokenizer(sent, return_tensors="pt", padding=True, truncation=True, max_length=512).to(device)
                    with torch.no_grad():
                        out = model(**inputs)

                    last_hidden = out.last_hidden_state[0].detach().cpu().numpy()  # (seq_len, hidden)
                    ids = inputs["input_ids"][0].tolist()
                    tokens = tokenizer.convert_ids_to_tokens(ids)

                    if level == "Token level":
                        special = {"[CLS]", "[SEP]", "[PAD]", "<s>", "</s>", "<pad>", "<unk>"}
                        for i, tok in enumerate(tokens):
                            if tok in special or (tok.startswith("[") and tok.endswith("]")):
                                continue
                            all_embeddings.append(last_hidden[i])
                            all_labels.append(f"{tok}|{sent[:20]}…" if len(sent) > 20 else f"{tok}|{sent}")
                    else:
                        mask = (inputs["attention_mask"][0].cpu().numpy() == 1)
                        mask[0] = False  # exclude [CLS]
                        idx = np.where(mask)[0]
                        if len(idx) >= 2:
                            mask[idx[-1]] = False  # exclude [SEP]
                        pooled = last_hidden[mask].mean(axis=0) if mask.any() else last_hidden[0]
                        all_embeddings.append(pooled)
                        all_labels.append(sent[:80] + "…" if len(sent) > 80 else sent)

            if len(all_embeddings) < 2:
                st.warning("Not enough points to plot (need at least 2). Try more sentences or token-level mode.")
            else:
                X = np.array(all_embeddings)
                pca = PCA(n_components=2)
                reduced = pca.fit_transform(X)

                fig = px.scatter(
                    x=reduced[:, 0],
                    y=reduced[:, 1],
                    text=all_labels,
                    title="BERT embeddings (PCA 2D)",
                )
                fig.update_traces(textposition="top center", mode="markers+text", textfont_size=9)
                fig.update_layout(
                    xaxis_title="PC1",
                    yaxis_title="PC2",
                    height=600,
                    showlegend=False,
                )
                st.plotly_chart(fig, use_container_width=True)
                st.caption(f"Points: {len(all_labels)} | Variance explained: {pca.explained_variance_ratio_.sum():.1%}")

# ----------------------------
# 5) Fill-mask
# ----------------------------
if active_tab == "Fill-mask":
    st.subheader("Masked language modeling (pipeline: fill-mask)")
    st.caption("For English BERT, use [MASK]. For RoBERTa-like models, mask token differs (e.g. <mask>).")

    with st.spinner("Loading fill-mask pipeline…"):
        fill_mask = load_fill_mask(model_name)

    mask_token = getattr(fill_mask.tokenizer, "mask_token", "[MASK]")
    st.write({"mask_token": mask_token})

    default_prompt = f"Peintre officiel de la marine et fondateur de la société {mask_token} des artistes français"
    prompt = st.text_area("Prompt with a mask token", value=default_prompt, height=90)

    top_k = st.slider("top_k", 1, 20, 5)

    if st.button("Run fill-mask"):
        try:
            results = fill_mask(prompt, top_k=top_k)
            # results: list[dict]
            out_df = pd.DataFrame(
                [{"sequence": r.get("sequence"), "score": float(r.get("score", 0.0)), "token_str": r.get("token_str")} for r in results]
            )
            st.dataframe(out_df, use_container_width=True, height=300)
        except Exception as e:
            st.error(f"fill-mask failed: {e}")
            st.info("Tip: make sure your prompt uses the right mask token for the selected model.")

	import streamlit as st
	import torch
	import numpy as np
	import pandas as pd
	from transformers import AutoTokenizer, AutoModel, pipeline
	from typing import Optional, Tuple, Dict, Any, List
	import json

	try:
	from sklearn.decomposition import PCA
	except ImportError:
	PCA = None
	try:
	import plotly.express as px
	except ImportError:
	px = None

	st.set_page_config(page_title="BERT – Tokenizer & Embeddings Demo", layout="wide")

	st.title("BERT – Architecture, Tokenizer, ID↔Token, Fill-Mask, Embeddings, PCA Map")

	# -----------------------------
	# Helpers
	# -----------------------------

	def _device() -> torch.device:
	return torch.device("cuda" if torch.cuda.is_available() else "cpu")


	def count_params(model: torch.nn.Module) -> Tuple[int, int]:
	total = sum(p.numel() for p in model.parameters())
	trainable = sum(p.numel() for p in model.parameters() if p.requires_grad)
	return total, trainable


	def safe_json(obj: Any) -> str:
	try:
	return json.dumps(obj, indent=2, ensure_ascii=False, default=str)
	except Exception:
	return str(obj)

	# ----------------------------
	# Sidebar: model selection
	# ----------------------------

	st.sidebar.header("⚙️ Settings")
	model_name = st.sidebar.text_input("Hugging Face model name", value="google-bert/bert-base-uncased")
	use_hidden_states = st.sidebar.checkbox("output_hidden_states", value=False)
	max_vocab_rows = st.sidebar.slider("Rows per page (vocab viewer)", 50, 2000, 500, step=50)

	device = _device()
	st.sidebar.write("Device:", str(device))


	@st.cache_resource(show_spinner=False)
	def load_tokenizer_and_model(model_name: str, output_hidden_states: bool):
	tok = AutoTokenizer.from_pretrained(model_name, use_fast=True)
	mdl = AutoModel.from_pretrained(model_name, output_hidden_states=output_hidden_states)
	mdl.eval()
	return tok, mdl


	@st.cache_resource(show_spinner=False)
	def load_fill_mask(model_name: str):
	# fill-mask uses AutoModelForMaskedLM under the hood when you pass model id
	return pipeline("fill-mask", model=model_name)


	with st.spinner("Loading tokenizer + model…"):
	tokenizer, model = load_tokenizer_and_model(model_name, use_hidden_states)
	model = model.to(device)

	# ----------------------------
	# "Tabs" controlled via session_state
	# (workaround so the active section does not reset to the first one)
	# ----------------------------
	TAB_LABELS = [
	"Architecture",
	"Tokenizer vocab",
	"ID ↔ Token",
	"Fill-mask",
	"Embeddings output",
	"Embeddings map",
	]

	if "active_tab" not in st.session_state:
	st.session_state["active_tab"] = TAB_LABELS[0]

	active_tab = st.radio(
	"Section",
	TAB_LABELS,
	index=TAB_LABELS.index(st.session_state["active_tab"]),
	horizontal=True,
	key="main_tab_selector",
	)
	st.session_state["active_tab"] = active_tab

	# ----------------------------
	# Architecture tab
	# ----------------------------

	if active_tab == "Architecture":
	col1, col2 = st.columns([1, 1])

	with col1:
	st.subheader("Infos générales")
	total, trainable = count_params(model)
	st.write(
	{
	"model_id": model_name,
	"model_class": model.__class__.__name__,
	"total_params": total,
	"trainable_params": trainable,
	"dtype": str(next(model.parameters()).dtype),
	"device": str(next(model.parameters()).device),
	}
	)

	st.subheader("model.eval()")
	st.write("✅ Le modèle est en mode évaluation (`eval()`).")

	st.subheader("config (model.config)")
	try:
	cfg = model.config.to_dict()
	except Exception:
	cfg = vars(model.config)
	st.code(safe_json(cfg), language="json")

	with col2:
	st.subheader("Architecture (str(model))")
	# éviter d'afficher 5000 lignes
	model_str = str(model)
	if len(model_str) > 12000:
	model_str = model_str[:12000] + "\n...\n[tronqué]"
	st.code(model_str)

	st.subheader("Couche d’input embeddings")
	try:
	emb_layer = model.get_input_embeddings()
	w = emb_layer.weight
	st.write(
	{
	"embedding_weight_shape": list(w.shape),
	"vocab_size (weight)": int(w.shape[0]),
	"hidden_dim": int(w.shape[1]),
	}
	)
	except Exception as e:
	st.warning(f"Impossible d’accéder à get_input_embeddings(): {e}")

	# ----------------------------
	# 1) Tokenizer vocab
	# ----------------------------
	if active_tab == "Tokenizer vocab":
	st.subheader("Tokenizer vocabulary")
	st.write({"len(tokenizer)": len(tokenizer), "model": model_name})

	# Efficient vocab browsing: build only the requested slice
	total = len(tokenizer)
	if total == 0:
	st.warning("Tokenizer vocabulary appears empty.")
	else:
	# page slider on ID range
	max_start = max(total - max_vocab_rows, 0)
	start = st.slider("Start ID", 0, max_start, min(1000, max_start), step=max_vocab_rows)
	end = min(start + max_vocab_rows, total)

	ids = list(range(start, end))
	# decode single id -> token string (close to your original)
	tokens = [tokenizer.decode(i) for i in ids]

	df = pd.DataFrame({"ID": ids, "token": tokens})
	st.dataframe(df, use_container_width=True, height=520)

	with st.expander("Special tokens"):
	st.write("special_tokens_map:", tokenizer.special_tokens_map)
	st.write("all_special_tokens:", getattr(tokenizer, "all_special_tokens", []))
	st.write("all_special_ids:", getattr(tokenizer, "all_special_ids", []))

	# ----------------------------
	# 2) ID ↔ Token conversion
	# ----------------------------
	if active_tab == "ID ↔ Token":
	st.subheader("Convert text → ids/tokens and ids → text")

	text = st.text_area(
	"Text to tokenize",
	value="Sustainable thermal insulation biocomposites from rice husk",
	height=100,
	)

	enc = tokenizer(text, return_tensors="pt")
	ids = enc["input_ids"][0].tolist()
	toks = tokenizer.convert_ids_to_tokens(ids)
	decoded_list = tokenizer.decode(ids, skip_special_tokens=False)
	decoded_clean = tokenizer.decode(ids, skip_special_tokens=True)

	c1, c2 = st.columns(2)
	with c1:
	st.markdown("input_ids")
	st.code(ids)
	st.markdown("tokens")
	st.code(toks)
	with c2:
	st.markdown("decode(ids) (keep specials)")
	st.code(decoded_list)
	st.markdown("decode(ids) (skip specials)")
	st.code(decoded_clean)

	st.divider()
	st.subheader("Single conversions")
	cc1, cc2 = st.columns(2)

	with cc1:
	st.markdown("ID → token")
	id_in = st.number_input("ID", min_value=0, max_value=max(len(tokenizer) - 1, 0), value=min(101, max(len(tokenizer) - 1, 0)))
	# decode([id]) gives the string form for that single id
	st.write({"id": int(id_in), "token": tokenizer.decode([int(id_in)])})

	with cc2:
	st.markdown("token → ID")
	tok_in = st.text_input("Token (as in vocab, e.g. 'insulation' or '##ing')", value="insulation")
	if tok_in:
	st.write({"token": tok_in, "id": int(tokenizer.convert_tokens_to_ids(tok_in))})

	# ----------------------------
	# 3) Embeddings output
	# ----------------------------
	if active_tab == "Embeddings output":
	st.subheader("Model forward → last_hidden_state")

	text2 = st.text_area(
	"Text for embeddings",
	value="Sustainable thermal insulation biocomposites from rice husk",
	height=90,
	)

	inputs = tokenizer(text2, return_tensors="pt").to(device)
	with torch.no_grad():
	outputs = model(**inputs)

	last_hidden = getattr(outputs, "last_hidden_state", None)
	if last_hidden is None:
	st.warning("This model output has no last_hidden_state (unexpected for AutoModel). Try another model.")
	else:
	toks = tokenizer.convert_ids_to_tokens(inputs["input_ids"][0].tolist())
	emb = last_hidden[0].detach().cpu().numpy() # (seq_len, hidden_dim)

	df = pd.DataFrame(
	emb,
	index=[f"{i} {t}" for i, t in enumerate(toks)],
	columns=[f"d{j}" for j in range(emb.shape[1])],
	)
	st.dataframe(df, use_container_width=True, height=520)

	# ----------------------------
	# 4) Embeddings map (multi-sentence)
	# ----------------------------
	if active_tab == "Embeddings map":
	st.subheader("Multi-sentence embeddings → PCA map")
	st.write("Enter several sentences (one per line). Embeddings are computed and projected to 2D for visualization.")

	default_sentences = "Sustainable thermal insulation biocomposites.\nRice husk and natural fibers.\nEnergy-efficient building materials.\nRecycled plastic composites.\nWood fiber insulation."
	sentences_text = st.text_area("Sentences (one per line)", value=default_sentences, height=120, key="embed_map_sentences")

	level = st.radio("Embedding level", ["Token level", "Sentence level"], horizontal=True, key="embed_map_level")

	if st.button("Compute embeddings and plot", type="primary", key="embed_map_btn"):
	lines = [s.strip() for s in sentences_text.strip().split("\n") if s.strip()]
	if not lines:
	st.warning("Enter at least one sentence.")
	elif PCA is None:
	st.error("scikit-learn is required for PCA. Install it with `pip install scikit-learn`.")
	elif px is None:
	st.error("plotly is required. Install it with `pip install plotly`.")
	else:
	with st.spinner("Computing embeddings…"):
	all_embeddings: List[np.ndarray] = []
	all_labels: List[str] = []

	for sent in lines:
	inputs = tokenizer(sent, return_tensors="pt", padding=True, truncation=True, max_length=512).to(device)
	with torch.no_grad():
	out = model(**inputs)

	last_hidden = out.last_hidden_state[0].detach().cpu().numpy() # (seq_len, hidden)
	ids = inputs["input_ids"][0].tolist()
	tokens = tokenizer.convert_ids_to_tokens(ids)

	if level == "Token level":
	special = {"[CLS]", "[SEP]", "[PAD]", "<s>", "</s>", "<pad>", "<unk>"}
	for i, tok in enumerate(tokens):
	if tok in special or (tok.startswith("[") and tok.endswith("]")):
	continue
	all_embeddings.append(last_hidden[i])
	all_labels.append(f"{tok}\|{sent[:20]}…" if len(sent) > 20 else f"{tok}\|{sent}")
	else:
	mask = (inputs["attention_mask"][0].cpu().numpy() == 1)
	mask[0] = False # exclude [CLS]
	idx = np.where(mask)[0]
	if len(idx) >= 2:
	mask[idx[-1]] = False # exclude [SEP]
	pooled = last_hidden[mask].mean(axis=0) if mask.any() else last_hidden[0]
	all_embeddings.append(pooled)
	all_labels.append(sent[:80] + "…" if len(sent) > 80 else sent)

	if len(all_embeddings) < 2:
	st.warning("Not enough points to plot (need at least 2). Try more sentences or token-level mode.")
	else:
	X = np.array(all_embeddings)
	pca = PCA(n_components=2)
	reduced = pca.fit_transform(X)

	fig = px.scatter(
	x=reduced[:, 0],
	y=reduced[:, 1],
	text=all_labels,
	title="BERT embeddings (PCA 2D)",
	)
	fig.update_traces(textposition="top center", mode="markers+text", textfont_size=9)
	fig.update_layout(
	xaxis_title="PC1",
	yaxis_title="PC2",
	height=600,
	showlegend=False,
	)
	st.plotly_chart(fig, use_container_width=True)
	st.caption(f"Points: {len(all_labels)} \| Variance explained: {pca.explained_variance_ratio_.sum():.1%}")

	# ----------------------------
	# 5) Fill-mask
	# ----------------------------
	if active_tab == "Fill-mask":
	st.subheader("Masked language modeling (pipeline: fill-mask)")
	st.caption("For English BERT, use [MASK]. For RoBERTa-like models, mask token differs (e.g. <mask>).")

	with st.spinner("Loading fill-mask pipeline…"):
	fill_mask = load_fill_mask(model_name)

	mask_token = getattr(fill_mask.tokenizer, "mask_token", "[MASK]")
	st.write({"mask_token": mask_token})

	default_prompt = f"Peintre officiel de la marine et fondateur de la société {mask_token} des artistes français"
	prompt = st.text_area("Prompt with a mask token", value=default_prompt, height=90)

	top_k = st.slider("top_k", 1, 20, 5)

	if st.button("Run fill-mask"):
	try:
	results = fill_mask(prompt, top_k=top_k)
	# results: list[dict]
	out_df = pd.DataFrame(
	[{"sequence": r.get("sequence"), "score": float(r.get("score", 0.0)), "token_str": r.get("token_str")} for r in results]
	)
	st.dataframe(out_df, use_container_width=True, height=300)
	except Exception as e:
	st.error(f"fill-mask failed: {e}")
	st.info("Tip: make sure your prompt uses the right mask token for the selected model.")