Detailed explanation of python basic knowledge

一.VariablesNaming rules

1.Variable names can only be any combination of letters, numbers, and underscores

2. Variable names cannot start with numbers

3. Some reserved words segments cannot be used as self-defined variables names

4 variable names It needs to have a clear meaning, such as a variable that saves a name, it is best to define it as a variable name such as name

2. Character encoding

The role of character encoding is to convert the input characters into Machine code. ASCII code is the earliest character encoding in the world. The earliest character encoding in China is GB2312, which contains more than 7,000 Chinese characters and symbols. After the first expansion, more than 20,000 Chinese characters were included. The character encoding is GBK1.0. The second After this expansion, a total of more than 27,000 Chinese characters were included, and the character encoding is GB18030. In order to unify character encoding internationally, Unicode character encoding was introduced because this encoding requires more storage space than the original ASCII encoding when storing English. Later, After compression optimization, UTF-8 character encoding was introduced. This encoding is still one character per byte when storing English, and three bytes when storing a Chinese character.

3. Python user interactive program

Python has a variety of interactive programs, which can also be called interpreters. The most commonly used interactive program is CPython, and the fastest code running speed is PyPy.

4.if judgment statement

#!/usr/bin/env python
age_of_oldboy = 56
guess_age = int(input("guess_age:"))
if guess_age == age_of_oldboy:
   print("yes,you got it.")
elif guess_age > age_of_oldboy:
   print("think smaller")
else:
   print("think bigger")

The function of this code is to allow the user to enter a number to guess the value of age_of_oldboy. It should be noted that in Python, when a line of code is not dependent on the above code The relationship needs to be entered in the top box, and when there is a subordinate relationship, a certain indentation needs to be used to express the subordinate relationship. Generally, it is indented four spaces. In addition, special statements that express judgment and looping, such as if, elif, else, while, for, etc., need to end with a : sign. This code is written in the environment of python3.X. In python2.X, do not add () to print. In python2.X, input() needs to be changed to raw_input().

5.while loop

age_of_oldboy = 56
count = 0
while count <3:
    guess_age = int(input("guess_age:"))
    if guess_age == age_of_oldboy:
       print("yes,you got it..")
       break
    elif guess_age > age_of_oldboy:
       print("think smaller...")
    else:
       print("think bigger")
    count += 1
    if count == 3:
       continue_confirm = input("do you want to guessing...")
      if continue_confirm != &#39;n&#39;:
         count = 0

break means to end the current loop, and countinue means to skip the following loop statement and start the next loop. You can write an else statement after the while loop. When the loop ends normally, that is, if no break, countinue, etc. actions have been performed, the actions under the else statement will be executed.

6. for loop

for count in range(3):
    guess_age = int(input("guess_age:"))
    if guess_age == age_of_oldboy:
       print("yes,you got it..")
       break
    elif guess_age > age_of_oldboy:
       print("think smaller...")
    else:
       print("think bigger")
else:
    print("sorry,you try too mary times..")
 
for i in range(0,10,2): #range(初值，条件，步长)
    print(i)

7. Quote Variable method

1 Use placeholder

name=input("name:")
age=input("age:")
job=input("job:")
salary=input("salary:")
info='''-----info of %s-----
Name:%s
Age:%s
Job:%s
Salary:%s
'''% (name,name,age,job,salary)

Use placeholder %s to indicate that the position needs to be filled with a string , followed by % It is the string used to fill the previous placeholder position, and the variable can be referenced at this position. Other placeholders include %d and %f respectively indicating filling with integer type and filling with floating point type

info2='''-----info of {_name}-----
Name:{_name}
Age:{_age}
Job:{_job}
Salary:{_salary}
'''.format(_name=name,_age=age,_job=job,_salary=salary)
info3='''-----info of {0}-----
Name:{0}
Age:{1}
Job:{2}
Salary:{3}
'''.format(name,age,job,salary)

8.''' The role of '''

1Multi-line comments

'''-----info of {0}-----
Name:{0}
Age:{1}
Job:{2}
Salary:{3}
'''

2Multi-line output

info3='''-----info of {0}-----
Name:{0}
Age:{1}
Job:{2}
Salary:{3}
'''
print(info3)

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