The mapping and dataframe demo (streamlit hello, select mapping option on left hand size, have "show code" checked) seems to be missing "import urllib" in the code section below the live demo;

The code uses except urllib.error.URLError as e: but urllib is never imported; copying and pasting the code into an app does show the import error.

Tested on streamlit 0.78.0, python 3.8.

EDIT 1: make it clearer
EDIT 2: Just realized the same thing happens for the Dataframe demo, edited.