Fixed import and stabilized YouTube transcript extraction

Ensured proper import of YouTubeTranscriptApi and simplified transcript fetching.
Resolves 'name not defined' and transcript retrieval errors.

app.py

@@ -1,94 +1,104 @@
+
+# YouTube Learning Assistant (Personalized MEM Style)
+# Stable Final Version – works on Hugging Face Spaces
+
+
 import streamlit as st
-from youtube_transcript_api import YouTubeTranscriptApi as yta
-from transformers import pipeline
 import re
+from transformers import pipeline
+import requests
 
+# Safe import of transcript library 
+try:
+    from youtube_transcript_api import YouTubeTranscriptApi
+except ImportError:
+    st.error("youtube-transcript-api not found. Make sure it’s in requirements.txt")
 
-# Helper functions
 
+# Helper Functions
 
-def extract_video_id(url):
-    """Extract YouTube video ID from a full URL."""
+
+def extract_video_id(url: str):
+    """Extract the 11-character YouTube video ID from any valid URL."""
     pattern = r"(?:v=|\/)([0-9A-Za-z_-]{11}).*"
     match = re.search(pattern, url)
     return match.group(1) if match else None
 
 
-def get_transcript(video_id):
-    """Fetch transcript text for a given video ID (compatible with all versions)."""
+def get_transcript(video_id: str) -> str:
+    """
+    Fetch the English transcript text for a given YouTube video.
+    Falls back to YouTube oEmbed check if unavailable.
+    """
     try:
-        # Standard way — works in most versions
+        # Standard transcript fetch
         transcript = YouTubeTranscriptApi.get_transcript(video_id, languages=['en'])
+        text = " ".join([t["text"] for t in transcript])
+        if not text.strip():
+            raise Exception("Transcript empty.")
+        return text
     except Exception as e:
-        # Fallback: try fetching manually from other available languages
-        try:
-            transcript_list = YouTubeTranscriptApi.list_transcripts(video_id)
-            transcript = transcript_list.find_transcript(['en']).fetch()
-        except Exception:
-            raise Exception(f"Transcript not available or video has no subtitles. Details: {str(e)}")
-
-    text = " ".join([t["text"] for t in transcript])
-    return text
-
+        # Graceful fallback: check if video exists / has captions
+        check = requests.get(f"https://www.youtube.com/oembed?url=https://www.youtube.com/watch?v={video_id}")
+        if check.status_code == 200:
+            raise Exception("Transcript not available — this video likely has no English subtitles.")
+        else:
+            raise Exception(f"Invalid video ID or unavailable video. Details: {str(e)}")
 
 
-def summarize_MEM_style(text):
-    """
-    Summarize transcript in MEM style:
-    simple, story-like, structured, and step-by-step.
-    """
+def summarize_MEM_style(text: str) -> str:
+    """Summarize transcript using MEM (Model Explanation Method)."""
     summarizer = pipeline("summarization", model="facebook/bart-large-cnn")
 
-    # Prepare chunks to fit within model limits (~1024 tokens)
-    max_chunk = 1000
-    text_chunks = [text[i:i+max_chunk] for i in range(0, len(text), max_chunk)]
-
+    max_chunk = 1000  # keep inside model token limit
+    chunks = [text[i:i + max_chunk] for i in range(0, len(text), max_chunk)]
     summary = ""
-    for chunk in text_chunks:
-        # Add MEM-style instruction to the input prompt
+
+    for chunk in chunks:
         prompt = f"""
-        Summarize and explain this text using the MEM (Model Explanation Method):
+        Summarize and explain this content using the MEM (Model Explanation Method):
         - Use simple, story-like language.
         - Explain step-by-step, as if teaching a beginner.
         - Focus on understanding, not technical detail.
-        - Keep the explanation calm, structured, and easy to remember.
+        - Keep tone calm, structured, and easy to remember.
 
         Text:
         {chunk}
         """
-        summary_part = summarizer(prompt, max_length=200, min_length=80, do_sample=False)[0]['summary_text']
-        summary += summary_part + " "
+        out = summarizer(prompt, max_length=200, min_length=80, do_sample=False)[0]['summary_text']
+        summary += out + " "
 
     return summary.strip()
 
 
 # Streamlit Interface
 
-st.set_page_config(page_title="🎥 YouTube Learning Assistant (MEM Style)", layout="centered")
-st.title("🎓 YouTube Learning Assistant (MEM Style)")
-st.markdown("Paste a **YouTube video link** below to generate its transcript and MEM-style explanation.")
+
+st.set_page_config(page_title="🎥  YouTube Learning Assistant (Personalized MEM Style)", layout="centered")
+st.title("🎓 YouTube Learning Assistant (Personalized MEM Style)")
+st.markdown("Paste a **YouTube video link** below to generate its transcript and a MEM-style explanation.")
 
 url = st.text_input("Enter YouTube URL:")
 
 if st.button("Generate MEM Summary"):
-    if url:
-        with st.spinner("Fetching transcript... please wait ⏳"):
-            video_id = extract_video_id(url)
-            if not video_id:
-                st.error("Invalid YouTube URL. Please check and try again.")
-            else:
+    if not url:
+        st.warning("Please paste a YouTube link first.")
+    else:
+        video_id = extract_video_id(url)
+        if not video_id:
+            st.error("Invalid YouTube URL. Please check and try again.")
+        else:
+            with st.spinner("Fetching transcript… please wait ⏳"):
                 try:
                     text = get_transcript(video_id)
-                    st.success("Transcript fetched successfully!")
-                    st.subheader(" Transcript (first 500 chars)")
-                    st.write(text[:500] + "...")
-                    
-                    with st.spinner("Creating your MEM-style summary... this may take a minute ⏳"):
+                    st.success("Transcript fetched successfully ✅")
+                    st.subheader("📝 Transcript Preview")
+                    st.write(text[:600] + "…")
+
+                    with st.spinner("Creating your MEM-style summary… ⏳"):
                         summary = summarize_MEM_style(text)
-                    st.subheader("MEM-Style Explanation")
+                    st.subheader("📘 MEM-Style Explanation")
                     st.write(summary)
 
                 except Exception as e:
                     st.error(f"Error: {str(e)}")
-    else:
-        st.warning("Please paste a YouTube link first.")