I am familiar with both Python and C++ as a programmer. I was thinking of writing my own simple web application and I wanted to know which language would be more appropriate for
If you'd like to avoid writing HTML, you could try GWT. However, in my experience, using an intermediate framework to generate HTML and ECMAScript never works anywhere near as well as hand-writing the pages.
[edit] nikow mentions in the comments that Pyjamas is a port of GWT to Python.
Regarding the language, if given the choice between C++ and Python I would pick Python 100% of the time. Even ignoring the obvious difference in abstraction between those languages, Python simply has more useful libraries than C++. You don't have to write your own development-oriented web server -- Django comes with one. You don't need to write a custom template library -- Python has Genshi. Django comes with a capable ORM layer, or for even more control you can use SQLAlchemy. It's barely a contest.