Consolidate some simple codes before the exam.

I wish everyone can pass, excellent!!

catalogue

  1. Simple output

2. for loop

3,eval()   Dequote

4. abs() absolute value   divmod() Division   pow() Power max min Min

5. Bit operation    & |  ^  ~    It should be a multiple-choice question

6. Escape character

7. Slice

8. Format output

9. String

10. for loop

11. Exception handling

12. List

13. tuple

14. Dictionary

15. set {,}

16. Documents

17. Dimensions of data organization   

18. Functions

20. random library

22. jieba participle

23. worldcloud word cloud

24. Overview of Python third-party libraries

  1. Simple output

print('Hello world!')

2. for loop

for i in range(10):
    if i%2==0:
        continue
    print(i)

3,eval()   Dequote
 

a=input("Please enter your name:") #Accept tpye(a) according to the character type
b=eval(input("Please enter your age: ")) #eval dequote
print("This is a string.")
print(a,b)
print("You are?{} ，you{}Yes".format(a,b))

4. abs() absolute value   divmod() Division   pow() Power max min Min

print(abs(-25))  #absolute value
print(divmod(10,3))  #Divide to get cells (3, 1)
x,y=divmod(10,3)  #Unpacking assignment cell
print(x,y,"\n")

print("pow(10,2)={}".format(pow(10,2)) ) #Calculate the y-power of x
print("pow(10,2,3)={}\n".format(pow(10,2,3)) ) #Calculate the y-power of x and take the remainder 3


print("max(1,2,3,4,6,4,8,9)={}".format(max(1,2,3,4,6,4,8,9)))
print("min(1,2,3,4,6,4,8,9)={}".format(min(1,2,3,4,6,4,8,9)))

5. Bit operation    & |  ^  ~    It should be a multiple-choice question

x=0b10101111
y=0b11111110             #One can be considered an opcode
print("0b10101111&0b11111110={}\n".format(bin(x&y)))#Bitwise and, 1 unchanged, 0 cleared
print("0b10101111|0b11111110={}\n".format(bin(x|y))) #Press bit or, 1 full 1, 0 unchanged

print("~0b10101111={}\n".format(bin(~x))) #Reverse by bit - 0b1011000
print("0b10101111^0b11111111={}\n".format(bin(x^y))) #By bit or, the use is unknown

print("0b10101111<<2={}".format(bin(x<<2))) #Shift left
print(x)
print("x<<2={}\n".format(x,x<<2)) #Shift left, shift left 1 bit, double

print("0b10101111>>2={}".format(bin(x>>2))) #Shift right with symbol

6. Escape character

print("123\n456")  # \n line feed
print("123\t456")  # \t tab 4 spaces
print("123\b")  # \b backspace 

7. Slice

Index with [], excluding the second bit,

Note that starting from bit 0

s='Computer level II Examination'
print(s[0:2])
print(s[-1:2])  #No result 
print(s[-1:2:-1])    #The result is grade two

8. Format output

Formatted output is most likely an operation problem,

s=eval(input("Please enter a string:"))
print("{:->20,}".format(s))

  To remember the position of the format, fill it first, then left and right, and then width

Chang Kao

For example: character class:

s='python'
print("{:*<20}".format(s))  #*Fill, left justified, 20 characters
print("{:\^20}".format(s))  # \Fill, center, 20 characters
print("{:.5}".format(s))    #Keep only the first 5 characters result: Python

{} is a placeholder and must be added, otherwise it is an ordinary string ":. 5"

It is mainly to fill in some characters for output

Digital class:

print("{:5,}".format(456789123))  #Width 5 (useful only if less than 5), comma separated result: 456789123

print("{0:b},{0:c},   {0:d},  {0:o},   {0:x},   {0:X}".format(520))
# Binary, Unicode character, decimal, octal, hexadecimal, hexadecimal
#1000001000,   Ȉ,       520,   1010,    208,     208

print("{0:e},    {0:E},        {0:f},        {0:%}".format(3.1415926))
#E exponential form e exponential form standard floating point form percentage form of floating point number
#3.141593e+00, 3.141593E+00, 3.141593,     314.159260%

print("{0:.2f}".format(3.1415926))
#Save two decimal places result: 3.14

9. String

Single string operation

s='Hello World'
print(str(s))   #Force type conversion to str
print(len(s))   #String length
print(s.count('or'),'\n')  #Number substring

print(s.lower())  #All lowercase, unchanged s  
print(s.upper(),'\n')   #All uppercase, without changing s, only when s = s.upper()

print(s.replace("He",'hh')) #he is replaced by hh and s remains unchanged
print(s.center(15,"*"),'\n')  #String centering function, fillchar parameter optional

print(s.split(' '))  #Returns a list with sep as the separation point, and sep is blank by default
print(s.strip("H")) #Removes the characters listed in chars to the left and right of the string str
print(s.join("123"),'\n') #Insert s as a separator into "123". Generally, s is like ','

print(s)  #s hasn't changed

Inter string operation

a='python'
b='520'
print(a+b)  #String connection
print(b*2)  #String copy
print(a in b)  #Does the string exist in

In particular, split(),strip(),join() is often used in operation questions

Chapter IV:

10. for loop

for loop variable   in   Combined variables (string, file, range() function, list, dictionary):     (don't forget the colon)

for i in range(1,4):
    print(i)

1.continue statement
Used to end the current loop, that is, jump out of the following unexecuted statements in the loop body, but do not jump out of the current loop.
2.break statement
Jump out of the innermost loop. After terminating the loop, continue execution from the code after the loop.

11. Exception handling

Single branch selection structure. The usage syntax is:

s=input('Please input number:')
while 1:
    try:
        s=int(s)
        print(s)
        break
    except ValueError:
        print("a number!! ")
        s=input("Please input number:")

try...except...else...
This structure can be regarded as a double branch structure,
The code in else is executed only when the code in try does not throw an exception.

try...except...finally...
In this structure, no matter whether an exception occurs in the try code or not, the code in the finally statement block will always be executed.
 

Exception handling structure for capturing multiple exceptions

try:
    <>
    Exception < exception type >:
        < Operation >
    Exception < exception type >:
        < Operation >

  Common errors

• ZeroDivisionError: division by zero # division error
• TypeError: Can't convert 'int' object to str implicitly   Program exception handling
• TypeError: unsupported operand type(s) for *: 'set' and 'int'   Operation type is not supported
• NameError: name 'name' is not defined   Variable name does not exist
• FileNotFoundError: [Errno 2] No such file or directory: 'wangyan.txt'   file does not exist
• TypeError: object of type 'int' has no len()   Parameter type mismatch

Chapter V: combination type

12. List

• A pair[   ] Inside, separated by commas;
• There is no length limit, element types can be different, and predefined lengths are not required
• Elements are in order, and indexes can be used
• Linear data structure
• The list is variable

Create list  

a_list=[1,'python',[5,2，0]]  #Create list directly
print(a_list)

s='python'
s_list=list(s)  #The list() function converts the iteratable object into a list (string)
print(s_list)  

ls=['book',23,[2010,'stud1'],20]   #Multilist nested list
print(ls[2][1][-1])

List operation method

s=list('woaiwangbingbing')
print(s)

The following code is manually copied into the IDLE Shell to run

s.count('a')  #Methods are followed by arguments, and () must have arguments
s.index('a',0,10)  #The first occurrence of the corner sign of the 'a' element, search from 0 to 10

s.append("h")   #The return value is none, indicating that it is modified locally and s has been changed
s.insert(-1,"0")   #If the return value is none, it means that it is modified locally. Finally, only the last bit can be pushed back, which is complementary to append
s.extend([1,2,3])  #Modify in place, which is equivalent to multiple append


del s[0]  #Delete function
s.remove('a')  #From left to right, delete an a
s.pop(0)  #Show s[0] and delete it from the list


s.reverse()  #Modify in place, reverse order
s.clear()  #clear list 
s.sort(key=None,reverse=True)   #No sort, flip
s.copy()   #Copy all elements in the list

  List operator

x=[1,2,3]
print(x)     #[1, 2, 3]
x=x+[4]  #You can add a list directly
print(x)     #[1, 2, 3, 4]
x+=[5]  #Self addition is also OK
print(x)     #[1, 2, 3, 4, 5]
x=x*2
print(x)    #[1, 2, 3, 4, 5, 1, 2, 3, 4, 5]

List related examples

a = [[1,2,3], [4,5,6], [7,8,9]]
s = 0
for c in a:  #c is an iterative variable, which is equal to [1,2,3], [4,5,6], [7,8,9] respectively
    for j in range(3): #j add the elements in c from 0, 1 and 2 
        s += c[j]  
print(s)  #So this is a double ergodic summation

13. tuple

• All elements are placed in parentheses ();
• If there is only one element, a comma must be added at the end, otherwise it will form a number instead of a tuple
• Creating empty tuples using tuples
• Support bi-directional indexing
• Tuples can be keys to dictionaries
• Tuples are immutable

Tuple creation

x=(1,2,3)
print(x[-1])

try :
    x[1]=1
except  TypeError:
     print('Tuple cannot change a value')

14. Dictionary

• dict() generates an empty dictionary
• A collection of keys and values connected by colons
• Key value pairs have no order and cannot be repeated
• Element types can be different
• Use curly braces{   } express
• The dictionary is stored as key value pairs, so the key is the index of the value
• Dictionaries are variable and can store any type

Establishment of dictionary

d=dict()

d={'name':'jack','age':'18','gender':'man'}

Dictionary lookup

d={'name':'jack','age':'18','gender':'man'}
print(d['name'])  Direct search key, with[ ]
try:
    d['123']
except KeyError:
    print("No key value pair")


print(d.keys())    #Return key, list form
print(d.values())   #Return value
print(d.items())   #Return key value, primitive form
print(d.get('key','default'))   #Check the key. If no value of defaul is returned, note that quotation marks must be added

Dictionary deletion

d={'name':'jack','age':'18','gender':'man'}

print(d.clear())    #Empty dictionary
print(d.popitem())    #Randomly take a key value pair (cell form) and delete it
print(d.pop(key,default))    #If the key exists, the corresponding value is returned, and the key value pair is deleted. Otherwise, the default value is returned

15. set {,}

• The elements in the collection are not repeatable
• Type can only be immutable
• Collection elements have no order and cannot be compared or sorted
• Curly braces {} indicate that there is no concept of index and location
• Can be created using set()

Set establishment

s={101,'python',23.2}
s=set()
s=set((1,2,5,4,2,1,4,3))  #lack order

Operation of collection

s={1,2,3,4,5}
t={3,4,5,6,7}


print(s-t)    #Only {1, 2}
print(s&t)    #Hand in {3, 4, 5}
print(s^t)    #Respective special {1, 2, 6, 7}
print(s|t)    #And {1, 2, 3, 4, 5, 6, 7}

The following code is manually copied into the IDLE Shell to run

s.add(x)      #Add element x
s.remove(x)   #Delete x, if none, KeyError exception
s.clear()     #Delete all, return to None and change locally
s.update( )   #Add a new element, return to None, and change it locally
s.pop()     #Randomly delete and return an element of the collection
x  in  s    #x is in the s set, judgment statement
x not in s 
s.discard(x)   #Specific delete x  

Chapter VI: Documents

16. Documents

File type: text file, binary file

File opening method:

How files are opened

Open mode	meaning
'r'	Read only mode. If the file does not exist, an exception FileNotFoundError is returned
'w'	Overwrite the write mode. If the file does not exist, it will be created. If it exists, it will be overwritten
'x'	Create a write mode. If the file does not exist, it will be created. If it exists, an exception FileExistsError will be returned
'a'	Append write mode. If the file does not exist, it will be created. If it exists, the content will be appended at the end of the file
'b'	Binary file mode
't'	Text file mode
'+'	It is used with r/w/x/a to add simultaneous reading and writing function on the basis of the original function

File operation

f=open('chapter6.txt','r')  #Open the file. Note that you must have a to open it
txt = f.read()      #read
txt_l = f.readline()  #Read a line
txt_ls = f.readlines() #Read in all rows to form a list for each behavior element
f.close()

f=open('chapter6.txt','w')  #Open the file. Note that you must have a to open it
f.write(txt)      #write
f.writelines(txt_ls)   #Write by list
f.close()

17. Dimensions of data organization   

csv data format

'''   One dimensional data: one dimensional data is composed of ordered or disordered data with equal relationship,
It is organized in a linear manner, corresponding to the concept of array in mathematics. ''
'''
Storage of one-dimensional data: separate the data with spaces, commas, line breaks or other symbols,
The comma separated storage format is called CSV format. ''

ls=['Tiananmen','the Imperial Palace','Jiuhua Mountain','Mount Huangshan']
fo=open('visity.csv','w')
fo.write(','.join(ls))
fo.close()

fi=open('visity.csv','r')
ls2=fi.read().strip('\n').split(',')  #strip removes' \ n 'on both sides, and split s are separated by', 'to form a list
print(ls2)
fi.close()

  two-dimensional

ls=[['scenic spot','Ticket Price'],['Tiananmen','15'],['the Imperial Palace','120'],['Jiuhua Mountain','160']]
fo=open('ticket.csv','w')
for row in ls :
    fo.write(','.join(row)+'\n')
fo.close()

fi = open('ticket.csv','r')
ls2=[]
for line in fi:
    ls2.append(line.strip('\n').split(','))
fi.close()
print(ls2)

#High dimensional data
'''
High dimensional data is composed of key value pair type data, which is organized in object mode and can be nested at multiple levels.
High dimensional data derives the syntax structure of specific data organizations such as HTML, XML and JSON.

'''

Chapter 7: function

18. Functions

#1 definition of function

def interchange(a,b):
    print(b,a)

interchange(1,3)

#2 functions with default values

• When using the formal parameter name, the parameter transfer order can be adjusted arbitrarily.
• Positional parameters must be passed in before keyword parameters.
• Position parameters cannot appear on the right of any default value parameter.
• The function is called multiple times and parameters are not passed for the default value parameter. The default value parameter is interpreted and initialized only once during definition.

def data(name,age=18):  #The default value can only be on the far right
    print(name+str(age)+'year')
data('Zhang San',126)
data('Li Si',26)

#3 keyword parameter transfer

def data(name,age=18):  #The default value can only be on the far right
    print(name+str(age)+'year')
data(age=180,name='Zhang San')  #Keyword parameter transfer, and the parameter transfer order can be adjusted arbitrarily

#4 variable length parameters*

*Param and * * param

• *param receives any number of parameters in a tuple
• **param receives any number of keyword parameters and puts them into the dictionary

def demo(*p):  #The feeling of the pointer
    print(p)
demo(1,2,'t')     #Results: (1, 2,'t ')

def demo1(**p):  #Reflect mapping relationship
    print(p)
demo1(a=1,b=2,c=3)   #Result: {a ': 1,' B ': 2,' C ': 3}

#5 sequence unpacking when passing parameters*

def demo(a,b,c):
    print(a*b*c)
lis = [2,3,4]
demo(*lis) #Unpacking assignment
#demo([2,3,4])  #This won't work because it's actually a parameter

tup = (3,4,5)
demo(*tup)   #Tuples can also be unpacked

dic={1:'a',2:'b',3:'c'}
demo(*dic)   #Unpack dictionary keys

def demo(a,b,c):
    print(a+b+c)
demo(*dic.values()) #Unpack dictionary values

set = {4,5,6}
demo(*set)  #Unpack collection

#6. Unpack the dictionary and transfer it to keyword reference

p={'a':1,'b':2,'c':3} 
def f(a,b,c):  #All keys in the dictionary must be formal parameter names of functions or correspond to two * variable length parameters.
    print(a,b,c)   
f(**p)    #Results: 1 2 3
''' #It is equivalent to passing a = 1, B = 2 and C = 3, which is a bit like keyword assignment
'''
def f(**p):
    for i in p.items():
        print(i)
p={'x':1,'y':2,'z':3}
f(**p)  
#Result: ('x', 1)
#      ('y', 2)
#      ('z', 3)

•     Multiple position variable parameters use an asterisk * in front of the formal parameter;
•     Multiple keyword variable parameters use two asterisks * * in front of the formal parameter;
•     Position variable parameters and keyword parameters can collect several arguments, multiple position variable parameters can be collected to form a tuple, and multiple keyword variable parameters can be collected to form a dict;
•     When mixed parameters are used, variable length parameters should be placed at the end of the parameter list, ordinary parameters should be placed in front of the parameter list, and position variable parameters should be placed before keyword variable parameters.

#7 the formal parameters in the function have nothing to do with the external arguments

def func(a,b):
    c=a**2+b
    b=a
    return c
a=10
b=100
c=func(a,b)+a

print('a=',a)         #a= 10
print('b=',b) #b It is not changed due to the assignment in the function   #b= 100
print('c=',c)            #c= 210

#8 function return value

• The return statement is used to end the function and return the program to the location where the function is called to continue execution;
• The return statement can appear in any part of the function;
• It can return the results of 0 or more function operations to the variable where the function is called at the same time;
• When return returns multiple values, the returned values form a tuple data type.

def cal(x,y):
    return x+y,x*y
print( cal(4,6) ) #return when multiple values are returned, they are in the form of cells. Obviously, they can't be changed. It's reasonable (10, 24)
a,b = cal(4,6)
print(a,b)   10 24

#9 scope of function

Local variables:

•     Naming rules are the same as identifiers
•     It is defined inside the function and is only valid inside the function. It is destroyed when the function exits

Global variables:

•     Naming rules are the same as identifiers
•     When a global variable is used inside a function, it needs to be declared with the global keyword, which has the same name as the global variable of the external variable
•     Variables defined outside the function are valid throughout the execution of the program

def demo():
    global x #Use externally defined variables
    x = 3
    y = 4
    print(x,y)
#x=6  #If it is not defined externally, it is defined internally
demo()
# print(y) #A function defined within a function cannot be used outside. An error is reported

x=3
def demo():
    print(x)#Exception. When global is not used in the function, it cannot be operated on
    x=x+1  
#    print(x)
demo()

#When a local variable has the same name as a global variable, the local variable will temporarily hide the global variable with the same name in its scope.
 

x=3
def demo():
    x=6
    print(x)  
demo()   #Output local variable 6 instead of global variable 3

#12 lambda function

    Anonymous functions are suitable for situations where a function similar to a function is temporarily needed but you don't want to define a function,
You can omit the function definition process and consider the function naming, so as to make the code more concise and readable.

myMax = lambda x,y : x if x>y else y   #Anonymous function for larger value
print(myMax(1,2))

Chapter 9: Python standard library

19. turtle Library

Import turtle Library

from turtle import * Import all, no more points
setup( )  Open directly

#Brush

setup( )  Open directly
fd(100) Go forward 100, (abbreviation)
backward(200) back off
seth(180 )  Abbreviation of rotation angle ,Absolute angle setheading
circle(100) Draw a circle, counterclockwise
circle(100,90) 90 radian
undo( ) revoke
right( ) Forward right, counterclockwise
left( ) Forward left, clockwise
goto( ) Moving to absolute coordinates will leave a moving track
speed( 1) Set brush speed, 1-10，Greater than 10, instant completion
dot(r,color ) Draw a circle with the brush as the center
home( ) Brush to the origin, facing east

#Brush state function

direct fd(10) No setup( ) Open
penup( )Pick up the brush, the brush can move, but there is no handwriting
pendown( ) Put down the brush
pensize( ) Brush thickness
pencolor( ) stroke color 
dot( ) Point a point
color( )Brush color, fill color
clear( ) empty
begin_fill( ) Before filling
end_fill( ) After filling
filling( ) stay begin_fill After that Ture,end_fill front
reset( )Empty, reset properties
write(' character string',font=('arial',20,'normal')
bgcolor( ) Canvas background color
hideturtle( ) Hide brush shapes
showturtle( ) Display shape
isvisible( ) Visible

example:

20. random library

Mason rotation algorithm is not a real random number. It is calculated by the algorithm

seed( ) Initializes the random number seed. The default is the current system time. It does not have to be set
 It is a seed that can generate a pile of random numbers in the same order
random( ) generate[0.0 , 1.0) Random decimal between
randint( a,b) generate[a, b]The integer between the left and right are closed intervals
getrandbitts(k )Generate memory k Random integer within
0b111 7 Max in memory 3
randrange(a,b[,c])generate[a,b) step c Random integer
uniform(a, b )generate[a,b]Random decimal between
choice( s) Returns a random element from a sequence
shuffle(s) Scramble the sequence and return
sample( p,k) from p Random selection in type k Elements returned as a list

choice( ls)   randint(a,b) is widely used

Example: # guessing games

from random import*
seed(0)
x = randint(0,100)
while 1:
    try:
        s=eval(input('enter a number:'))
        if s==x:
            print('bingo!')
            break
        elif s>x:
            print("Big")
        else:
            print('Small')
    except:
        print('************')

21,time

Time processing, time formatting, timing

from time import *
time( ) Returns the timestamp, floating-point number, in seconds, and the number of seconds elapsed from the starting point to the present
localtime(time stamp )Return time, structure form, default to current time
asctime(localtime())  Standardized output time structure
ctime(time stamp )Returns the normalized time string. The default is the current time
gmtime( ) Almost and localtime equally
mktime(gmtime()) Returns the number of seconds
time( )
mktime(gmtime( )) Return timestamp
process_time( ) cpu Running time, y-x Calculable program running time
sleep(3) cpu Sleep, not counting time
time( ) Subtraction can count sleep()Time
perf_counter( )Program timing can be performed

 # Formatted output of time:

strftime('%a %b %d %H %: M :%S  %Y',gmtime()) Time structure required

Y-year,
m-month (01-12), B-month (January), B-month abbreviation
d-day date (01-31)
A-week, a-week abbreviation
H-hour (24), I-hour (12)
M-minutes (00-59)
S-seconds (00-59)
p - morning and afternoon (AM,PM)

It's actually a placeholder to format the output
strptime(x) go back and find the timestamp

Chapter 10: third party Library

22. jieba participle

import jieba
jieba.lcut('character string')
jieba.lcut('character string',cut_all=True)
jieba.lcut_fot_search("character string")
jieba.add_word("Word package")  Add word pack

23. worldcloud word cloud

from worldcloud import WorldCloud
txt="text"
words = jieba.lcut(txt)  #jieba word segmentation of txt string
worldcloud = WorldCloud(font_path= 'Font path'，
width = ,height='',mask= 'Word cloud shape'
font_step= Font size step interval
max_font_size= Maximum font size
max_words = Maximum number of times, 200 by default
stopwords = Excluded list 
background_color = Picture background color_)  #Beautification work

worldcloud.generate(text) 
worldcloud.to_file(filename)  #Which file to save as

24. Overview of Python third-party libraries

Please ignore Chinese automatically. Chinese is just for memory

1. Web crawler
import requests
requests.get()

  2. Data analysis
numpy   number   Number (ndim dimension, shape array shape, number of size elements, itemsize memory size)
scipy  
pandas   
redis-py   data storage
PyMongo data storage   Monte mountain energy storage
seaborn marine data

3. Text processing direction
pdfminer   pdf Text
openpyx1   
beautifulsoup4   Beautify text, parse and process HTML and XML
SnowNLP   Natural language processing   Show show text
xpinyin   Pinyin   Chinese character to Pinyin
NLTK natural language processing

4. Data visualization
matplotlib   image processing
TVTK   three-dimensional
mayavi   After visualization, it's may  
vispy 

5. User graphical interface
PyQt5   Image interface   Pq5 generation 5 image
wxPython     Wechat interface
PyGTK   gif picture

6. Machine learning
lscikit - learn
TensorFlow   flow thinking surge
Theano 
mxnet   Neural network node
keras   Kress intelligence
PyTorch torch

 

7. Web development
Django     Zhang gou
Pyramid   ramid   Remi website
Flask   flash -- Web site
pylons     Long long website

8. Games  
pygame 
2Panda3D       2D, 3D games
3cocos2d

9. More
PIL   image processing
SymPy 
WeRoBot WeChat official account
MyQR QR code
loso natural language processing
Luminoth   machine vision
TimeSide network audio processing framework
PyOCR image recognition

Like third-party libraries, standard libraries need to be import ed when used