Question

how many parameters are required for write function

Answer 1

three orfour parameters indicates one of two problems: The function is doing too much. It should be split into several smaller functions, each which have a smaller parameter set.

Answer 2

Creating Functions

Overview

Teaching: 30 min 
Exercises: 0 min

Questions

How can I define new functions?

What’s the difference between defining and calling a function?

What happens when I call a function?

Objectives

Define a function that takes parameters.

Return a value from a function.

Test and debug a function.

Set default values for function parameters.

Explain why we should divide programs into small, single-purpose functions.

At this point, we’ve written code to draw some interesting features in our inflammation data, loop over all our data files to quickly draw these plots for each of them, and have Python make decisions based on what it sees in our data. But, our code is getting pretty long and complicated; what if we had thousands of datasets, and didn’t want to generate a figure for every single one? Commenting out the figure-drawing code is a nuisance. Also, what if we want to use that code again, on a different dataset or at a different point in our program? Cutting and pasting it is going to make our code get very long and very repetitive, very quickly. We’d like a way to package our code so that it is easier to reuse, and Python provides for this by letting us define things called ‘functions’ — a shorthand way of re-executing longer pieces of code. Let’s start by defining a function fahr_to_celsius that converts temperatures from Fahrenheit to Celsius:

def fahr_to_celsius(temp): return ((temp - 32) * (5/9))



The function definition opens with the keyword deffollowed by the name of the function (fahr_to_celsius) and a parenthesized list of parameter names (temp). The body of the function — the statements that are executed when it runs — is indented below the definition line. The body concludes with a return keyword followed by the return value.

When we call the function, the values we pass to it are assigned to those variables so that we can use them inside the function. Inside the function, we use a return statement to send a result back to whoever asked for it.