Add example app source files for st.pagination (#1492)

Add widget.pagination.py (basic usage) and widget.pagination_dataframe.py
(paginated dataframe) to support the embedded app demos referenced in the
st.pagination docstring at doc-pagination.streamlit.app and
doc-pagination-dataframe.streamlit.app.

Co-authored-by: blackary <>

Author: blackary

python/api-examples-source/widget.pagination.py

@@ -0,0 +1,4 @@
+import streamlit as st
+
+page = st.pagination(num_pages=10)
+st.write(f"Showing page {page}")

python/api-examples-source/widget.pagination_dataframe.py

@@ -0,0 +1,15 @@
+import streamlit as st
+import pandas as pd
+
+df = pd.DataFrame({"A": range(100), "B": range(100, 200)})
+rows_per_page = 10
+total_pages = (len(df) + rows_per_page - 1) // rows_per_page
+
+# Use placeholders to show dataframe above pagination
+dataframe_slot = st.empty()
+with st.container(horizontal_alignment="right"):
+    page = st.pagination(num_pages=total_pages)
+
+start_idx = (page - 1) * rows_per_page
+end_idx = start_idx + rows_per_page
+dataframe_slot.dataframe(df.iloc[start_idx:end_idx])