If you've been experimenting with Python, as I have, then you might notice that some words are saved for some certain processes. For example lambda is one of these words. I tried to use it as a variable name. it will usually highlight in blue if it is important. So an alternative is to use lamb_da or lamb_duh etc.
Other words include:
Langtangen, H. P. (2012). A Primer on Scientific Programming with Python (3rd ed.). Heidelberg: Springer. doi:10.1007/978-3-642-30293-0