The function of annotation
The classification and grammar of annotations
Characteristics of annotation
By using a familiar language , In the program, some codes are annotated , That's what annotations do , Can greatly enhance the readability of the program .
Annotations fall into two categories ： Single line comments and multi line comments
Single-line comments
Only one line can be annotated , The grammar is as follows ：
# The comment
Multiline comment
You can annotate multiple lines of content , It is usually used to comment a piece of code , The grammar is as follows ：
""" The first line notes Second line of notes The third line notes …… """ ''' notes 1 notes 2 notes 3 …… '''
Be careful ： The interpreter does not execute any comment content
summary
The function of annotation
Is it treated in a language familiar to humans? Explain it , Convenient later maintenance .
Classification of notes
Single-line comments ：# The comment , Shortcut key Ctrl+/
Multiline comment ：""" The comment """ perhaps ''' The comment '''
The interpreter does not execute annotation content
Role of variables
Defining variables
Understanding data types
Example experience ： Let's go to the library to read , How to quickly find the books you want ？ Is the administrator putting the book in a fixed position in advance , And numbered this position , We only need to search the designated location according to this number in the library to find the books we want .
This number is actually a name for the shelf where the books are stored , Easy to find and use later .
In the program , Data is temporarily stored in memory , To find or use this data more quickly , Usually we define a name after storing this data in memory , The name is the variable .
A variable is just the name of the memory address where the current data is stored .
Variable name = value
Variable name customization , To satisfy the identifier naming rules
2.1 identifier
Identifier naming rules Python A unified specification for defining various names in , As follows ：
By digital 、 Letter 、 Underline composition
Cannot start with a number
You can't use built-in keywords
Case sensitive
False None True and as assert 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
2.2 Naming habits
See the name and know the meaning
Hump ： That is, every word is capitalized , for example ：MyName
Little hump ： the second （ contain ） Later words are capitalized , for example ：myName
Underline ： for example ：my_name
my_name='Tom' print(my_name) schoolName=" Black horse programmer " print(schoolName)
stay Python In order to meet different business needs , Also divide the data into different types
# int—— integer
num1 = 1
# float—— floating-point , It's a decimal
num2 = 1.1
# str—— character string , characteristic ： Data should be quoted
a = 'hello whorld'
# bool—— Boolean type , Usually used in judgment . Boolean has two values ：True and False
b = True
# list—— list
c = [10,20,30]
# tuple—— Tuples
d = (10,20,30)
# set—— aggregate
e = {10,20,30}
# dict—— Dictionaries ： Key value pair
f={'name':'TOM','age':'18'}summary
The syntax for defining variables
Variable name = value
identifier
By digital 、 Letter 、 Underline composition
Cannot start with a number
You can't use built-in keywords
Case sensitive
data type
integer ：int
floating-point ：float
character string ：str
Boolean type ：bool
Tuples ：tuple
aggregate ：set
Dictionaries ：dict
Debug The tool is pycharm IDE Tools integrated in to debug programs , Here, the programmer can view the execution details and process of the program or mediation bug.
Debug How to use the tool ：
Breaking point
Debug debugging
Breakpoint location
The first line of code of the code block to be debugged by the target can , That is, a breakpoint .
The way to interrupt
Click the blank space to the right of the line number of the object code .
Format output
Format symbol
f- character string
print The terminator
Output
effect ： Program output content to users
demand ： Output “ My age this year is 18 year ”
The so-called formatted output is to output content in a certain format .
1.1 Format symbol
%s character string %d Signed decimal integers %f Floating point numbers %c character %u An unsigned decimal integer %o Octal integer %x Hexadecimal integer （ A lowercase letter ox）%X Hexadecimal formal （ Capitalization OX）%e Scientific enumeration （ A lowercase letter 'e'）%E Scientific enumeration （ Capitalization 'E'）%g%f and %e Abbreviation %G%f and %E Abbreviation skill %06d, Indicates the number of integer display digits of the output , not enough 0 completion , If it exceeds the current digit, it will be output as is
%.2f, Represents the number of decimal places displayed after the decimal point
'''
1、 Prepare the data
2、 Format symbol output data
'''
age = 18
name = 'TOM'
weight = 75.5
stu_id = 1
# 1、 My age this year is x year —— Integers %d
print(' My age this year is %d year '%age)
# 2、 My name is X—— character string %s
print(' My name is %s'%name)
# 3、 My weight is x kg —— Floating point numbers %f
print(' My weight is %f kg '%weight)
print(' My weight is %.2f kg '%weight) Be careful ： This one has two decimal places
# 4、 My student number is x
print(' My student number is %d'%stu_id)
print(' My student number is %03d'%stu_id) Be careful ： This integer is expressed in 3 Bit integer display
# 5、 My name is x, This year, x Year old
print(' My name is %s, This year, %d Year old '%(name,age))
# 5.1 My name is x, This year, x Year old
print(' My name is %s, This year, %d Year old '%(name,age+1))
# 6、 My name is x, This year, x Year old , weight x kg , The student number is x
print(' My name is %s, This year, %d Year old , weight %.2f kg , The student number is %03d'%(name,age,weight,stu_id))
print(' My name is %s, This year, %s Year old , weight %s kg '%(name,age,weight))1.2 f'{ expression }'
Format string except %s, It can also be written as f'{ expression }'
name='TOM'
age=18
# My name is X, This year, X Year old
print(f' My name is {name}, This year, {age} Year old ')f- The format string is Python3.6 New formatting method in , This method is easier to read
1.3 Translate characters
\n: Line break
\t: tabs , One tab key （4 A space ） Distance of
print("hello \n world")
print("\t abcd")1.4 Terminator
Think about it , Why two print Will wrap output ？
print(' Output content ',end="\n")stay Python in ,print(), Default by oneself
end="\n"This newline Terminator , So it leads to every two print Direct line feed display , Users can change the terminator as required
summary
Format symbol
%s： Format output string
%d： Format output integers
%f： Format output floating point number
f- character string
f'{ expression }'
Escape character
\n： Line break
\t： tabs
print Terminator
print(' Content ',end="")Syntax of input function
Input input Characteristics
1.1 The role of input
stay Python in , The function of the program to accept the data entered by the user is to input .
1.2 Input syntax
input(" Prompt information ")1.3 The characteristics of input
When the program is executed to input, Waiting for user input , After the input is completed, continue to execute down
stay Python in ,input After receiving user input , Generally stored in scalar , Easy to use
stay Python in ,input The received data input by any user will be treated as a string .
password=input(' Please enter your password ：')
print(f' The password you entered is {password}')The necessity of data type conversion
Common methods of data type conversion
ask ：input() The data received from the user is of string type , If user input 1, I want to know how to operate an integer ？
answer ： Convert the data type , Convert string type to integer
int(x[,base]) take x Convert to an integer float(x) take x Convert to a floating point number complex(real[,imag]) Create a complex number ,real It is the real part ,imag It is the imaginary part str(x) Put the object x Convert to string repr(x) Put the object x Converts to an expression string eval(str) Used to calculate the validity in a string Python expression , And returns an object tuple(s) The sequence of s Converts to a tuple list(s) The sequence of s Convert to a list chr(x) Convert an integer to a Unicode character ord(x) Converts a character to its ASCII An integer value hex(x) Convert an integer to a hexadecimal string # 1、float()—— Convert data to floating point num1 = 1 str1 = '10' print(type(float(num1))) # float print(float(num1)) # 1.0 print(float(str1)) # 10.0 # 2、str()—— Convert data to string type print(typr(str(num1))) #str # 3、tuple()—— Convert a sequence into tuples list1 = [10 ,20 ,30] print(tuple(list1)) #(10 ,20 ,30) # 4、list()—— Convert a sequence into a list t1 = (100 ,200 ,300) print(list(t1)) #[100 ,200 ,300] # 5、eval()—— Calculate the validity of in string Python expression , And returns an object str2 = '1' str3 = '1.1' str4 = '(1000 ,2000 ,3000)' str5 = '[1000 ,2000 ,3000]' print(type(eval(str2))) # int print(type(eval(str3))) # float print(type(eval(str4))) # tuple print(type(eval(str5))) # list
summary
Common functions for converting data types
int()
float()
str()
list()
tuple()
eval()
Master the functions of common operators
Arithmetic operator
Assignment operator
Compound assignment operator
Comparison operator
Logical operators
Be careful ：
Mixed operation priority order ：() higher than ** higher than *///% higher than +-
= The result on the right is assigned to the variable on the left of the equal sign Single variable assignment
num = 1 print(num)
Multiple variable assignments
num1,float1,str1=10,0.5,'hello world' print(num1) print(float1) print(str1)
Many variables are given the same value
a = b = 10 print(a) print(b)
Be careful ：
The operation order is to operate the calculation on the right side of the compound assignment operator first , Then perform the compound assignment operation
Comparison operators are also called relational operators , Usually used to judge
expand — Logical operations between numbers
a=0 b=1 c=2 # and Operator , As long as a value of 0, The result is 0, Otherwise it turns out to be the last non 0 Numbers print(a and b)#0 print(b and a)#0 print(a and c)#0 print(c and a)#0 print(b and c)#2 print(c and b)#1 # or Operator , Only all values are 0, The result is 0, Otherwise it turns out to be the first non 0 Numbers print(a or b)#1 print(a or c)#2 print(b or c)#1
Priority of arithmetic operations
Mixed budget priorities ：() higher than ** higher than *///% higher than +-
Assignment operator
=
Compound assignment operator
+=
-=
priority
Let's start with the expression to the right of the compound assignment operator
Then calculate the arithmetic operation of compound assignment operation
Final assignment operation
Comparison operator
Judge equal ：==
Greater than or equal to ：>=
Less than or equal to ：<=
It's not equal to ：!=
Logical operators
And ：and
or ：or
Not ：not
Conditional statements work
if sentence
if……else……
Multiple judgments
if nesting
Suppose a scenario ：
Have you ever been to an Internet cafe at this age ？
What is the one thing you must do when you go to an Internet cafe to surf the Internet ？
Why give the ID card to the staff ？
Is it to judge whether you are an adult ？
If adults can surf the Internet ？ If you are not an adult, you are not allowed to surf the Internet ？
In fact, the so-called judgment here is conditional statement , namely If the condition holds, execute some code , If the condition does not hold, the code will not be executed
2.1 grammar
if Conditions : Conditional execution code 1 Conditional execution code 2 ……
2.2 Quick experience
if True:
print(" Conditional execution code 1")
print(" Conditional execution code 2")Demand analysis ： If the user is older than or equal to 18 year , That's adult , Output “ Has reached adulthood , You can go online ”
3.1 Simple version
age=20
if age>=18:
print(" Has reached adulthood , You can go online ")
print(" System off ")3.2 premium
New demand ： Users can output their own age , And then the system decides whether or not you're an adult , Adults export “ Your age is ‘ The age entered by the user ’, Has reached adulthood , You can go online ”.
# input String type when accepting user input data , On the condition that age And integers 18 Do judgment , So here it is int Convert data type
age = int(input(" Please enter your age ："))
if age >= 18:
print(f' Your age is {age}, Has reached adulthood , You can go online ')
print(' System off ')effect ： Implementation of conditions if Code below ; Conditions not established , perform else Code below
reflection ： Examples of Internet cafes , If you grow up , Allow access to the Internet , If you're not an adult ？ Should we reply that users can't access the Internet ？
4.1 grammar
if Conditions ： Conditional execution code 1 Conditional execution code 2 …… else： Code executed when the condition does not hold 1 Code executed when the condition does not hold 2 ……
4.2 Utility version ： Internet cafes surf the Internet
age = int(input(" Please enter your age ："))
if age >= 18:
print(f' The age you entered is {age}, Has reached adulthood , You can go online ')
else:
print(f' The age you entered is {age}, Children , Go home and do your homework ')Be careful ： If some conditions are true, the relevant code is executed , In other cases, the code interpreter will not execute
reflection ： The legal working age in China is 18~60 year , That is, if the age is less than 18 Child labor at the age of , illegal ; If the age is 18~60 The legal length of service is between two years old ; Greater than 60 The legal retirement age is 15 years old .
5.1 grammar
if Conditions 1: Conditions 1 Set up the code to execute 1 Conditions 1 Set up the code to execute 2 …… elif Conditions 2: Conditions 2 Set up the code to execute 1 Conditions 2 Set up the code to execute 2 …… …… else: None of the above conditions holds. The executed code
Multiple judgments can also be related to else In combination with . commonly else Put it all over if At the end of the sentence , Indicates the code to be executed when none of the above conditions is true .
age = int(input(" Please enter your age ："))
if age < 18:
print(f" The age you entered is {age}, Child labor ")
elif (age >= 18) and (age <= 60): # perhaps elif 18<=age<=60:
print(f" The age you entered is {age}, legal ")
elif age > 60:
print(f' The age you entered is {age}, retired ')reflection ： By bus ： If you have money, you can get on the bus , You can't get on the bus without money ; When you get on the bus, if you have a seat available , You can sit down ; If there are no empty seats , It's about standing . How to write a program ？
6.1 grammar
if Conditions 1: Conditions 1 Set up the code to execute 1 Conditions 1 Set up the code to execute 2 …… if Conditions 2： Conditions 2 Set up the code to execute 1 Conditions 2 Set up the code to execute 2 ……
Be careful ： Conditions 2 Of if Also out of conditions 1 Inside the indent relationship
6.2 example ： By bus
money = 1
seat = 0
if money == 1:
print(" Local tyrants , Please get in the car ")
if seat == 1:
print(" There are vacant seats , Sit down ")
else:
print(" There are no empty seats , Stand and wait ……")
else:
print(" friend , No money , Run with me , Run faster ")Ternary operators are also called ternary operators or ternary expressions .
7.1 grammar
If the condition is true, the expression of execution if Conditions else An expression executed when the condition is not true .
Quick experience ：
a = 1 b = 2 c = a if a > b else b print(c)
if Sentence syntax
if Conditions : Conditional execution code
if……else……
if Conditions : Conditional execution code else: Code executed when the condition does not hold
Multiple judgments
if Conditions 1: Conditions 1 Set up the code to execute elif Conditions 2: Conditions 2 Set up the code to execute else: None of the above conditions holds. The executed code
if nesting
if Conditions 1: Conditions 1 Set up the code to execute if Conditions 2: Conditions 2 Set up the code to execute ……
Ternary operator
If the condition is true, the expression of execution if Conditions else An expression executed when the condition is not true
