There are two keyword to define a function in Python: "def" and "return". The structure is always the same: def function_name(input1, input2 = 2): [INDENT] "main body" return output Remember that in Python using the ":" at the end of the definition line and indenting the following lines is essential. Every output is placed after the keyword return. The inputs can be mandatory or optional. Every optional input need to be given a default value, like this: optional_input = Default_value. Finally, it is good practice to put all the mandatory inputs first, and then the optional ones.