II. Data type

One Basic types of variables

One Immutable

️ A single element in a variable cannot be modified , increase , Delete

1 character string - str - string

2 integer - int - integer

3 floating-point - float

4 Tuples - tuple

(1, 2, 3, " university ")

Two Variable form

1 Dictionaries - dict - dictionary

{'name' : 'Nice', 'age' : 35}

2 list - list - dictionary

[1, 2, 3, 3.14, ' university ']

3、 ... and Common commands

1. len() Determine the length of the string

2. type() Judge the type of variable

3. id() Address corresponding to output variable

Two character string

1. Python Middle single quotation marks and double quotation marks are used exactly the same

2. Use three quotation marks to specify a multiline string

3. word = 'String'
   sentence = "This is sentence"
   paragraph = """This is a paragraph
   that can consist of multiple lines"""

4. Escape character ： The backslash

# ** Be careful ** #
1.  Escape symbols cannot appear at the end of a string 

1. Backslash can be used to escape , Use r You can keep the backslash from escaping . Such as ：r"this is a line with \n" be \n Will be displayed , They don't execute

2. Concatenate strings literally . Such as ："this" "is" "string" Will be automatically converted to this is string

3. String can be used + Operator Connect together , use * Operator repeat

4. Python There are two ways to index strings in , From left to right 0 Start , From right to left -1 Start

5. Python String in cannot be changed

6. Python No separate character type , One character is the length of 1 String

7. Syntax format of string interception ： Variable [ Header subscript ： Tail subscript ： step ]

8. str = '123456789'
   print(str)                
   print(str[0:-1])          # Output all characters from the first to the last 
   print(str[0])             # Output the first character 
   print(str[2:5])
   print(str[2:])            # Output all characters after the third start 
   print(str[1:5:2])          
   # Running results ：24
   print(str * 2)             # Output string twice 
   print(str + 'GAME OVER!')   # Connection string 
   print(r'GAME OVER!\n')      # Use  r  You can keep the backslash from escaping 

3、 ... and “ The amount ” All kinds of changes

One example

# Other data types -> character string 
my_age = 18
my_new_age = str(my_age)
# Other data types -> Integers 
room_number = "520"
room_new_number = int(room_number)
# Other data types -> Floating point numbers 
ticket_price = "3.5"
ticket_new_price = float(ticket_price)

Two matters needing attention

1. Floating point to integer will eliminate the decimal part

2. A non integer number in the string cannot be converted to an integer

3. Non integer in string cannot be converted to floating point

4. String or integer to floating point number , There is one more decimal after the integer

Four Math library math The common method of

One Python Built in mathematical functions

1. The absolute value abs()

2. minimum value min()

3. Maximum max()

Two Python math Library math functions

️ Note that you need to import import math

1. Take the whole number up ceil()

2. Take the whole number down floor()

3. Square root sqrt()