Before introducing Python variables and data types, we also need to understand the reserved words and identifiers in Python.

Reserved words: some words are given special meanings in Python, and these words cannot be used when naming objects.

# View reserved words in Python
import keyword
print(keyword.kwlist)

# Reserved word list
'''['False', 'None', 'True', '__peg_parser__', 'and', 'as', 'assert', 'async', 
'await', 'break', 'class', 'continue', 'def', 'del', 'elif', 'else', 'except', 
'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is', 'lambda', 
'nonlocal', 'not', 'or', 'pass', 'raise', 'return', 'try', 'while','with','yield']'''

Identifier: the name given to variables, functions, classes, modules, and other objects.

Naming rules: letters, numbers and underscores are strictly case sensitive. They cannot start with numbers or be named with reserved words.

1. Definition and use of variables

A variable is a box with labels, which can put the required data into it. It consists of three parts:

Identification: indicates the memory address stored by the object, which can be obtained by using the built-in function id();

Type: represents the data type of the object, which can be obtained by using the built-in function type();

Value: represents the specific data stored by the object. You can use the print() function to print.

name = "michael"
print(name, id(name), type(name))

'''name Is a variable name, which can be customized;
"= "Is an assignment operator, which can assign a value to a variable;
"michael"This string is the value'''

# Output results
michael 2623526618800 <class 'str'>

Variables, called variables, can be changed. After multiple assignments, the variable name will point to the new space.

name = "michael"
print(name, id(name), type(name))
# Reassign name
name = "jackson"
print(name, id(name), type(name))

# Output results
'''As you can see, name The memory address of the variable is changed, which proves that it points to the new space,
And disconnect from the original address, and the original memory address will also become memory garbage'''
michael 2787167717040 <class 'str'>
jackson 2787163459952 <class 'str'>

2. Data type of Python

Integer type: int (98)

Floating point type: float (3.14)

String type: str ("michael jackson")

Boolean type: bool (True, False)

a = 98
b = 3.14
c = "michael jackson"
d = True
# Print data type
print(type(a), type(b), type(c), type(d))

# Output results
<class 'int'> <class 'float'> <class 'str'> <class 'bool'>

2.1 integer type

English is integer, abbreviated as int, which can represent positive numbers, negative numbers and zero.

Different decimal representations of integers:

Base system	Basic number	Representation method	example
Decimal (default)	0,1,2,3,4,5,6,7,8,9	Default representation	118
Binary	0,1	Start with 0b	0b111010
octal number system	0,1,2,3,4,5,6,7	Start with 0o	0o116
hexadecimal	0,1,2,3,4,5,6,7,8,9 A,B,C,D,E,F	Start with 0x	0x76

a = 118
b = 0b111010
c = 0o116
d = 0x76
print(a, b, c, d)

# Output results
118 58 78 118

2.2 floating point number type

It consists of integer part and decimal part.

Storage imprecision: when using floating-point number type for calculation, the number of decimal places may be inaccurate.

e = 3.1415
print(e, type(e))

n1 = 1.1
n2 = 2.2
print(n1+n2)

'''Floating point number calculation has uncertainty, so we need to introduce Decimal library'''

from decimal import Decimal
print(Decimal("1.1")+Decimal("2.2"))

# Output results
3.1415 <class 'float'>
3.3000000000000003
3.3

2.3 string type

Also known as immutable character sequence, it can be defined with single quotation marks, double quotation marks (must be on one line) or three quotation marks (multiple lines).

str1 = "michael"
str2 = 'jackson'
str3 = '''michael
jackson'''
print(str1, type(str1))
print(str2, type(str2))
print(str3, type(str3))

# Output results
michael <class 'str'>
jackson <class 'str'>
michael
jackson <class 'str'>

2.4 boolean type

Used to represent true or False values. True is true and False is False.

Boolean values can also be converted to integers, true -- > 1, false -- > 0.

f1 = True
f2 = False
print(f1, type(f1))
print(f2, type(f2))
print(1+f1)
print(1+f2)

# Output results
True <class 'bool'>
False <class 'bool'>
2
1

3. Data type conversion

Splice data of different data types together.

Function name	effect	matters needing attention	example
int()	Convert other data types to integers	1. Text and decimals cannot be converted to integers 2. Convert floating-point number to integer and erase it	int("123") int(9.8)
float()	Convert other data types to floating point numbers	1. Text cannot be converted to floating point number 2. Convert integer to floating point number, and add. 0 at the end	float("9.9") float(9)
str()	Convert other data types to strings	You can also use quotation marks to convert	str(123) "123"

a1 = "michael"
a2 = 18
a3 = 98.5
print("My name is"+a1+"，this year"+str(a2)+"Years old, my grades are"+str(a3))

print(type(a1), type(a2), type(a3))
print(type(str(a2)), type(int(a3)))

# Output results
 My name is michael，I am 18 years old and my grade is 98.5
<class 'str'> <class 'int'> <class 'float'>
<class 'str'> <class 'int'>