[Python for Hikari-] Chapter 06-01 Functions (Intrinsic Functions and Function Definitions)

[Python] Chapter 06-01 Built-in functions and function definitions

From this chapter, we will explain about Functions. Functions are a concept that appears in any programming language, not just Python. Let's hold it down.

Speaking of functions, I think I learned linear and quadratic functions in mathematics when I was in junior high school and high school. For example, the following quadratic function,

f(x) = x^2+3x+4

When there is, if x = 2

f(2) = 2^2+3.2+4
=14

I was able to ask.

Even in a program, if you enter some value like x = 2 above, you can define a function that ** returns a value **. This time I would like to see how to create that function.

Built-in functions

In fact, you've probably touched on things like ** print, int, str, len, sorted, range **, etc. in the past. Let's actually see it. Enter the following code from the ** Python Console **.

>>> str = 'hello'
>>> len(str)
5
>>> ls = [1, 2, 3, 4, 5]
>>> len(ls)
5

I explained it with ** len function ** now, but it is the same as specifying x = 2 above, and if you put a string variable or list variable in len, the length (or number of elements) will be returned. I will come.

Not only ** len function **, but ** print function, int function, str function, sorted function, range function ** are functions originally prepared in Python. These functions are called ** built-in functions **. There are many built-in functions. You can check the built-in functions and usage from the links below.

https://docs.python.org/ja/3/library/functions.html

In addition, using a function is often referred to as ** "calling a function" **.

Create your own function

I mentioned the built-in functions prepared in advance, but you can also create and use the functions yourself. This is called ** Function Definition **.

By using function definitions, long programs can be divided into parts for each role, and readability is improved.

There are the following methods to actually define the function.

def Self-made function name(argument):
What is executed when the function is called

The first ** def ** means a definition, such as defining, and is a description that defines a function. Then, define the function name you created, add **: ** (colon) as in the case of if statement and while statement, and then describe the processing contents in the function.

In addition, about the above ** argument (hikisu) **, this is the place to enter the value such as ** x = 2 ** earlier. I would like to explain this next time.

I'll show you an example of a function from now on, but first I'd like to explain it without any arguments. Create a new chap06 </ font> and create a file with the file name samp06-01-01.py </ font> in it. Create it and write the following code. Simply put, you can think of it as a function for greeting.

def greet_func():
    print('Running inside a function')
    print('Hello!')

def greet_func():
    print('Running inside a function')
    print('Hello!')

print('From now on greet_Call the func function.')

#greet_Call the func function
greet_func()

print('The processing inside the function is finished!')

def greet_func():
    print('Running inside a function')
    print('Hello!')

def morning_func():
    print('The morning function was called.')
    print('Good morning!')

def afternoon_func():
    print('The daytime function was called.')
    print('Hello!')

def night_func():
    print('The night function was called.')
    print('Good evening!')

#Where to enter numbers
judge = int(input('Enter 0 for morning, 1 for noon, 2 for night:'))

if judge == 0:
    morning_func()
elif judge == 1:
    afternoon_func()
elif judge == 2:
    night_func()
else:
    print('Please enter the correct value.')