Basic data types and strings

1, Variable

1. Three elements of variables: variable name, variable value and variable data type

2. Format: variable name = variable value

3. Output variable: Print (variable name)

""" variable """
# 1,Three elements of variables: variable name, variable value and data type of variable value
# 2,Define the format of the variable: variable name = Variable value
money = 1080  # Variable name ---> money  Variable value ---> 1080  Data type of variable ---> int
# 3,Output variables: print(Variable name)
print(money, type(money))  # type() View the data type of the variable

4. Naming rules for variables

• Variable names are composed of letters, numbers and underscores (numbers cannot start)

• Case sensitive (A and a are two different variables)

• Do not conflict with keywords and system reserved words

"""Naming rules for variable names"""
# Variable names are composed of letters, numbers and underscores (numbers cannot start)
a = 6
print(a, type(a))
a2 = 'Hello World'
print(a2, type(a2))
student_name = 'Zhang Shengsheng'
print(student_name, type(student_name))
# Case sensitive( A,a Are two different variables)
A = 3
a = 6
print(A)
print(a)
# Do not conflict with keywords and system reserved words(in,on,class)

2, Data type and data type conversion

1. Data type

• Integer type (int): indicates integer -- > 1, - 2235

• Floating point type: represents decimal -- > 1.5, 3.14, 88.5;

• String type (str): 'hello'

• Boolean: indicates true / false judgment -- > true / false

• Null value type (None): indicates that there is no -- > blank and no data

  ------->Get the value type in the data: type() function

"""data type"""
# Integer type( int): Represents an integer
age = 12
print(age, type(age))
# Floating point type( float): Represents a decimal
high = 178.9
print(high, type(high))
# String type( str): 'hello'
name = "Li Zijie"
print(name, type(name))
# Boolean type( bool): Indicates true or false judgment --->True/False
a = True
b = False
print(a, type(a))
print(b, type(b))
# Null type( None): It means nothing ---> Blank, no data
address = None
print(address, print(address))     

2. Data type conversion

• Function int(): int (str()), int(float()) str are integers and will not be rounded

• Function float(): float (str()), float(int())

• Functions str(): str (int()), str(float())

• Function bool():bool(""), bool(0), bool(None) False, other True

"""Data type conversion"""
# 1,function int() : int(str()),int(float())  str Itself is an integer and will not be rounded(round()function)
a = "65"  # String to integer type, which must be in integer form
print(type(a))
charge_a = int(str(a))
print(type(charge_a))  # String to floating-point type must be in decimal form
b = "3.58"
print(type(b))
charge_b = float(str(b))
print(type(charge_b))
# 2, function float() : float(str()) , float(int())
c = "3.58"
print(type(c))
charge_c = float(str(c))
print(type(charge_c))
c1 = 88
print(c1, type(c1))
charge_c1 = float(int(c1))
print(c1, type(charge_c1))
# function str() : str(int()),str(float())
d = 22
print(type(d))
charge_d = str(int(d))
print(type(charge_d))
d1 = 3.15
print(type(d1))
charge_d1 = str(float(d1))
print(type(charge_d1))
# function bool():bool(" "),bool(0),bool(None) False   rest True
f = 6
e = 9
print(bool(f))
print(bool(e))
print(bool(""))
print(bool(0))
print(bool(None))

3, Operator

1. Arithmetic operator

• Addition, subtraction, multiplication and division (+, -, *, /)

• Power (* *)

• Only the division of the integer part of the result (/ /) is retained

• Surplus (%)

"""Arithmetic operator """
# Addition, subtraction, multiplication and division(+,-,*,/)
a = 6
b = 7
print(a + b)  # 13
print(a - b)  # -1
print(a * b)  # 42
print(round(a / b, 2))  # round()Keep the specified decimal places and will be rounded
# Power(**)
c = 9
print(c ** 2)
print(c ** 3)
# Division that preserves only the integer portion of the result(//)
d = 6
f = 5
print(d // f)
# Surplus(%)
a1 = 11
a2 = 5
print(a1 % a2)

2. Assignment operator

operator	describe
=	Simple assignment operator
+=	Additive assignment operator
-=	Subtraction assignment operator
*=	Multiplication assignment operator
/=	Division assignment operator
%=	Modulo assignment operator
**=	Power assignment operator
//=	Rounding assignment operator

"""Assignment Operators """
# =    Simple assignment operator 
a = 5  # The right is assigned to the left
print(a)
# +=    Additive assignment operator
a1 = 3
a1 = a1 + 1
a1 += 2
print(a1)
# -=    Subtraction assignment operator
b = 10
b = b - 1
b -= 1
print(b)
# *=    Multiplication assignment operator
c = 3
c = c * 3
c *= 2
print(c)
# /=    Division assignment operator
d = 6
d = d / 3
d /= 3
print(round(d, 2))
# %=    Modulo assignment operator
e = 1
e = e % 2
e %= 1
print(e)
# **=    Power assignment operator
f = 3
f = f ** 3
f **= 4
print(f)
# //=Rounding assignment operator
g = 10
g = g // 6
g //= 6
print(g)

3. Comparison operator

operator	describe
==	be equal to
!=	Not equal to
>	greater than
<	less than
>=	Greater than or equal to
<=	Less than or equal to

"""Comparison operation"""  # The result is bool Boolean value
# ==be equal to
# !=Not equal to
# >    greater than
# <    less than
# >=Greater than or equal to
# <=Less than or equal to
a = 6
b = 8
print(a == b)  # F
print(a > b)  # F
print(a < b)  # T
print(a >= b)  # F
print(a <= b)  # T
print(a != b)  # T

4. Logical operator

operator	Logical expression	describe
and	x and y	x. If y is true, it is true. If one is false, it is false
or	x or y	x. If one of y is true, it is true, and both are false and false
not	not x	If x is false, not x is true

"""Logical operator"""
a = 9
b = 10
# and    x and y    x,y All true is true, and one false is false
print(a < b and b > a)
# or    x or y    x,y If one is true, it is true, and both are false and false
print(a + b > b and a + b < a)
# not    not x    If x False, then not x For true
print(not a > b)

5. Member operator

operator	describe
in	Returns True if a value is found in the specified sequence, otherwise False.
not in	Returns True if no value is found in the specified sequence, otherwise False.

 

"""member operator """
list_a = [1, 5, 8, 9, 45]
# in Returns if a value is found in the specified sequence True，Otherwise return False. 
print(1 in list_a)
print("a" in list_a)
# not in Returns if no value is found in the specified sequence True，Otherwise return False. 
print("b" not in list_a)
print(45 not in list_a)

6. Identity operator (id() function)

operator	describe
is	is determines whether two identifiers refer to an object
is not	is not determines whether two identifiers are referenced from different objects

 

# Variable data structure( list)，Even if it looks the same, the memory address is different
# Immutable data type(Integer, string)，If they look the same, their memory addresses are the same

"""Identity operator"""
# id()function
a = 6
b = 4
c = 6
print(id(a))
print(id(b))
print(id(c))
list_a = [123456, "321"]
list_b = [2, 8, 9]
print(id(list_a))
print(id(list_b))
# is  Is to determine whether two identifiers refer to an object
print(a is c)
print(a is b)
print(list_a is list_b)
# is not  Determines whether two identifiers are referenced from different objects
print(a is not b)
print(list_a is not list_b)
print(a is not c)

4, String and escape character

1. String format

• Single line:

str_a = "this is a str"

• Multiline

str_b =
""" 
This is a string
 Who am I?
"""

# Format:
# Single line
name = "Li Zijie"
print(name, type(name))
name2 = "Zhang" \
        "l"
print(name2)
# Multiline
str_a = """I'm fine today, don't you think"""
str_b = """Everybody
 I have a present"""
print(str_a, type(str_a))
print(str_b)

2. Escape character

Escape character	describe	effect
\n	Line feed	Print wrap
\	Escape character	Print characters with special meaning
\t	Tab	Empty 4 characters

"""Escape character"""
# \n Line feed
print("hello everyone!\n The show begins")
# \ Escape character
print("hello everyone!\\n The show begins")
# \t Tab 4 characters empty
print("hello everyone!\t The show begins")

3. String format match

Symbol	describe
%c	Formatted characters and their ASCII codes
%s	format string
%d	Format integer
%u	Format unsigned integer
%o	Format unsigned octal number
%x	Format unsigned hexadecimal number
%X	Format unsigned hexadecimal number (upper case)
%f	Format floating-point numbers to specify the precision after the decimal point
%e	Formatting floating point numbers with scientific counting
%p	Format the address of a variable with a hexadecimal number

"""String format match"""
print("Hello, my name is%s" % "Li Zijie" + "\n I this year%d" % 21, "\n My rise%s" % "179.9")

4. String splicing (literal interpolation of string)

• "str".format()

Set the specified location in the default order	"{}{}".format("h","e")
Set specified location	"{0}{1}".format("h","e")
Pass variables by name	My name is {name}. I'm {age} years old format(name = "Zhang Hu", age = 8)

"""String splicing"""
# Set the specified location in the default order  "{}{}".format("h","e")
print("This is{}{}".format("h", "e"))
# Set specified location"{0}{1}".format("h","e")   Indexes
print("This is{1}{0}".format("h", "e"))
# Pass variables by name "My name is{name}，this year{age}year".format(name = "Zhang Hu",age = 8)
print("My name is{name}，this year{age}year".format(name="Zhang Hu", age=8))

• f"xxxx{}

name = "Li Zijie"
age = 20
print(f"My name is{name}，this year{age}")

• +: you need to ensure that each variable value must be of string type

print("Hello, my name is%s" % "Li Zijie", "!I this year%d" % 21 + "My rise%s" % "179.9")

5, String common API

1. Conversion string of jion list

"""jion List conversion string"""
list_a = ['a', 'p', 'p', 'l', 'e']
print("".join(list_a))

2. split data segmentation operation

"""split Data segmentation operation"""
a = "apple red"
print(a.split(" "))
b = "hello world"
print(b.split(" "))

3. replace replaces the target string with the desired character

""" replace Replace the target string with the desired character"""
a = "My name is lizijie"
print(a)
print(a.replace("lizijie", "lizihao"))

4. strip removes leading and trailing spaces

""" replace Replace the target string with the desired character"""
a = " My name is lizijie "
print(a)
print(a.strip())