[Python Variable]Name Convention, how to check data type etc.

This article shows basics of variables in Python.

Proper understanding of variable naming conventions improves code readability.

Variable name conventions in Python

In the beginning, I show variable name convention in Python.

Basics of variable name conventions

The following three types of characters can be used in the variable name.

・Alphabet
・Numbers
・'_' : Underscore

Examples of variable names are as follows

test = 100
test1 = 100
test_1 = 100

Simple, but this is the only variable name conventions.

Variable names must be determined while following these conventions and avoiding prohibitions.

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Prohibitions of Variable name

There are three main prohibitions on naming variables.

・Cannot use "number" at the "beginning" of a variable
・Cannot use Reserved Keywords
・Cannot use Symbols

I show these three prohibitions in order.

--- Cannot use "number" at the "beginning" of a variable ---

### syntax error
1a = 100

--- Cannot use Reserved Keywords ---

"if", "for", and other strings that are reserved keywords in Python cannot be specified as variable names.

### syntax error
if = 1

The following are examples of reserved keywords that cannot be used as variable names.

if
True
import
as
return
not
etc.

--- Cannot use Symbols ---

### error
a&b = 1

The following are examples of symbols that cannot be used as variable names.

@
.
+
-
*
%
/
etc.

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Variable Declaration in Python

Other programming languages, such as C, require "variable declaration and variable type declaration" when using variables.

Python, however, does not require this "variable declaration".

In Python, the type of variable is automatically determined.

Comparison of variable declaration in C and Python

--- C ---

int a
a = 1

--- Python ---

a = 1

Python is easier.

However, be aware that dynamic variable declaration in python can also cause bugs.

Examples of bugs in Python

Here is an example of a bug caused by dynamic variable declaration in Python.

Variables of numeric type are overwritten with string.

num = 100
fruit = 'Apple'

num = fruit

sum = num + 1
# >> TypeError: can only concatenate str (not "int") to str

"num" was initially variable of numeric type, but has become string type in the process.

Therefore, addition will cause "TypeError".

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Variable types

Here are the main data types in Python.

Data Type		Description	Example
Numeric	Interger	Numeric type without decimal point	num = 100
	float	Numeric type with decimal point	num = 1.14
	Complex number	Denote imaginary units with j	a = 1 + 2j
Sequence Type	Strings	enclose with ' ' or " "	fruit = 'Apple'
	Tuple	・Defined with ( ) ・Separate with , ・Elements cannot be changed.	(1, 2, 3)
	List	・Defined with [ ] ・Separate with , ・Elements can be changed.	[1, 2, 3]
Set		・Defined with { } ・Duplicate elements are ignored. ・Elements are not ordered.	set1 = {1, 2, 3, 3, 1, 2} print(set1) # {1, 2, 3}
Dictionary		・Defined with { } ・Combination of key and value	price = {"apple":100, "banana":200, "orange" : 100}
Boolean		・True, False	is_ok = True

I give a supplementary explanation about sequence type.

Sequence type is the type that stores multiple elements.

String type is also a member of the sequence type since it contains multiple characters.

fluit = 'Apple'
for char in fluit :
    print(char)
 
###Output###
#A
#p
#p
#l
#e

The elements of the string "Apple" are taken one by one and displayed.

You can see that string type is also sequence type because the elements can be taken out one by one.

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How to check variable types

The data type can be checked by using type() function.

num = 100
fruit = 'Apple'
is_ok = True


print(num, type(num))
print(fruit, type(fruit))
print(is_ok, type(is_ok))

###Output###
# 100 <class 'int'>
# Apple <class 'str'>
# True <class 'bool'>

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How to convert variable types

Data types can be converted.

Below are the main type conversion functions.

int() : Conversion to integer type.
float() : Conversion to float type.
str() : Conversion to string type.

num = "1"
print(type(num))

###Output###
#<class 'str'>

num = int(num)
print(type(num))

###Output###
#<class 'int'>

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【Appendix】Naming Conventions other than variable

As a supplement, I also show naming conventions other than variable.

Item	Rule	Example
Package	・All lowercase ・Underscore is deprecated	tqdm, requests
Module	・All lowercase ・Underscore is available	sys, os
Class	・First letter is uppercase ・Delimiter : uppercase	MyFavoriteClass
Exception	・First letter is uppercase ・Delimiter : uppercase	MyError
Method	・All lowercase ・Delimiter : underscore	my_favorite_method
Function	・All lowercase ・Delimiter : underscore	my_favorite_funcion
Variable	・All lowercase ・Delimiter : underscore	my_favorite_instance
Constant	・All uppercase ・Delimiter : underscore	MY_FAVORITE_CONST

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