In this chapter, you've learned how to write and call functions of your own. We've explored scope and namespace issues, talked about argument passing, saw a number of functional tools such as lambda and map , and studied new function- related statements def , return , and global . We've also talked a little about how to go about gluing functions together, and looked at common function cases that can trip up new users. In Chapter 5 we'll learn about modules, which, among other things, lets you group functions into packages of related tools.