Study from Python Hour3: Functions

When I tried to do something with Python, I first searched for a sample script and somehow executed it.
7 hours I want to hit REST API with automatic execution, check the result, and even operate the VM
This time how to use the function. From the prepared functions to the functions you create yourself.

Learning materials

Learn the basics in just one day! A super introduction to Python
https://a.r10.to/hbHMiv

Past posts

environment

Windows
Python Ver3 series

The function that came out this time

print()
len()
str() / int()
sorted () * Sorted. ascending order? Tuple? Let's leave it here
abs()

Function naming convention

Basically the same as variables
Reserved words (reserved words if or NG in Python)
Variable names starting with numbers (1a or NG)
Generally, there are many rules for "word __word" such as my _ function ().

How to use the function

What only functions can do. So-called primitive processing such as hitting the OS or hardware. That's right with print ()
Complexity makes processing easy. That's right, sorted ().
Eliminate code duplication. You don't write similar code over and over to improve readability and maintainability.

Try using the function: sorted

Try sorting the list

org_list = [1, 20, 19, 4, 3]
sort_list = sorted(org_list)

print('org_list'+ str(org_list))
print('sort_list'+ str(sort_list))

Try to run

>test09_function.py
org_list[1, 20, 19, 4, 3]
sort_list[1, 3, 4, 19, 20]

I think you can sort and write by yourself, but you only need one line.

Create an original function

How to use the function (definition / argument / return value)

def function name (argument 1, argument 2):

Processing

Processing

Return Return value

Let's make the previous process a function

If you give a list, display the original list and the sorted list (try coding without looking at anything for the first time here)

def my_sort(org_list):

	sort_list = sorted(org_list)

	print('org_list'+ str(org_list))
	print('sort_list'+ str(sort_list))
	return
	
my_list = [1, 20, 19, 4, 3]
my_sort(my_list)

Try to run

>test10_myFunction.py
org_list[1, 20, 19, 4, 3]
sort_list[1, 3, 4, 19, 20]

Oh, it worked in one shot. I'm happy.

Function notes

Define the function first
Python needs to be declared before calling a function to process from the beginning of the file. Main processing later.

Function: Check arguments and return values

Earlier I tried a function with simple arguments. The return value is not dealt with in particular. Check the arguments and return value a little more here
There are the following cases about the return value
Case where return is not written >> Return value: None
Case of handling return without argument >> Return value: None
Case where return is handled with arguments >> Return value: Specified argument

Return value

Check the return value

def my_function1(a):
	print('in function1:'+ str(a))
	
def my_function2(b):
	print('in function1:'+ str(b))
	return

def my_function3(c):
	print('in function1:'+ str(c))
	return 1
	
def my_function4(d):
	print('in function1:'+ str(d))
	return 'aaa'

aa = my_function1(5)
print (aa)

bb = my_function1(10)
print (bb)

cc = my_function1(15)
print (cc)

dd = my_function1(20)
print (dd)

Try to run

>test11_myFunction2.py
in function1:5
None                                <<<Return value without return
in function2:10
None                                <<<Return value of return with no arguments
in function3:15
1                                   <<<return value of return 1
in function4:20
aaa                                 <<< return 'aaa'Return value of

It's uselessly long, but I was able to confirm what I wanted to confirm.
You can return not only numbers but also strings

argument

Function arguments can be handled as follows
Handle multiple arguments
"Keyword argument" that allows you to specify arguments in no particular order
Arguments with an undetermined number (variadic arguments)
Any number of arguments such as print () are OK
Multiple arguments and keyword arguments

  def my_function(arg1, arg2, arg3):
  	print(str(arg1)+str(arg2)+str(arg3))
  	aa = arg1 * arg2 * arg3
  	print(aa)
  	return
  
  my_function(2, 3, 4)
  
  my_function(arg2=2, arg1=3, arg3=4)

Try to run

>test12_myFunction_arg.py
234
24
324   <<<Passed arguments out of order
24    <<<Naturally the result is the same

How to use the help function

help (function name)

>>> help(print)
Help on built-in function print in module builtins:

print(...)
    print(value, ..., sep=' ', end='\n', file=sys.stdout, flush=False)

    Prints the values to a stream, or to sys.stdout by default.
    Optional keyword arguments:
    file:  a file-like object (stream); defaults to the current sys.stdout.
    sep:   string inserted between values, default a space.
    end:   string appended after the last value, default a newline.
    flush: whether to forcibly flush the stream.

>>> help(print)

If you think that print just prints, you can specify a delimiter or write to a file. Sometimes when you don't want to start a new line at the end.

About namespaces and function types

Namespace is the range that variables can handle.
Variables declared inside or outside the function
Variables defined inside a function cannot be used outside the function.
Variables defined outside the function can be referenced inside the function. It seems that it cannot be overwritten
There is something about global variables, but it is not recommended, so I will omit it.

Try using built-in functions

range function
A function that creates a serial number of numbers

  a = range(5)
  b = range(2, 5)
  
  print(a)
  print(list(a))
  
  print(b)
  print(list(b))
  
  
  for i in range(4, 7):
  	print(i)

Try to run

>test13_range.py
range(0, 5)         <<<Even if 0 is omitted, range(0, 5)Becomes
[0, 1, 2, 3, 4]
range(2, 5)
[2, 3, 4]
4                  <<<<It seems that it can be used in a for statement
5
6

This summary

Try to use and create functions for simple tasks
It took about 2 hours to think while taking notes

For Quotations / Lightning Talk

Qiita's markdown is not displayed well, but I will continue to copy and paste from Typora
Next time is object-oriented ..... can you understand?