File foundation - read / write, storage

Document basis ：

Common codes ：
ASCLL Encoding table ： common 0 yes 48;A yes 65;a yes 97
• 8 Bit binary represents a character
• Capable of representing letters 、 Numbers etc.

UTF-8 Can compile Chinese

Python Common library ：

1. os A large number of operation files are provided 、 Directory method .
2. pathlib2 File system path operation
3. openpyxl operation Excel file .
4. python-docx operation Word file .
5. python-pptx operation PowerPoint file .
6. opencv-python Image processing module , It provides powerful image processing related functions .

Open file ：
Open a file , And return the file object , In the process of file processing, you need to use the operation after opening the file

open(file, mode=‘r’) #mode= Write but not write

Use open() Methods must ensure that the file object is closed , That is to call close() Method
file: It's necessary , File path （ Relative or absolute paths ）“ file name ”.
mode: Optional , File open mode .

1. ‘r’ Reading documents （read）
2. ‘w’ Writing documents （write）
3. ‘a’ Append content at the end of the file （append）
4. ‘b’ Binary （ image file 、binary）
5. ‘t’ text file （text）
6. '+' Reunite with （r+： Reading and writing 、 Write from scratch ;w+： Reading and writing 、 Read / write after emptying the source file ）

Close file ：
Use open() Methods must ensure that the file object is closed , That is to call close() Method .

file.close()

But use with ….as…., Implicit call close() Method to close the file

with open(‘file.txt’, ‘r’) as f:
Close file . After closing, the file can no longer be read or written . No input close

File attribute ：

1. file.name： Return the name of the file ;
2. file.mode： Return to open file , File open mode adopted ;
3. file.encoding： Returns the encoding format used to open the file ;
4. file.closed： Judge whether the document has been closed .

practice ：

f=open("lzs.txt",'r')
print(f.closed) # Check whether the file is closed , It is not closed at this time , Returns the Flase
f.close()# Open before, close now 
print(f.closed)# It will return to True
with open("lzs.txt",'r')as f:  # Open with this 
    print(f.closed) # At this time, judge whether to close , return Flase; It should be in the file 
print(f.closed)# Now outside the file , return True

with open("lzs.txt",'r',encoding="utf-8")as f: # The document is in Chinese , To change the coding table , use encoding
    x=f.readlines()  
    for i in x:
        print(i,end="")

Read the file ：

function read（）： A separate read Errors will be displayed if there are Chinese characters or Chinese symbols in the reading , The reason is that the codes are different , So add... Later encoding="utf-8”, Transcoding can output Chinese .

Read the contents of the file byte by byte or character by character , When there are parameters , Read parameter bytes or characters ;

with open("lzs2.txt",'r')as f:
    x=f.read() # Self understanding ： Read byte , character , Numbers ;（6） The number in the middle represents how many ,6 The delegate reads 6 individual 
	print(x,end=" ")#  Price end=" "  The reason is that there will be a blank line after the function output , It can be used end=" "  To delete .

with open("lzs.txt",'r',encoding="utf-8")as f:  # This file is in Chinese , It can be output , The document is in Chinese , To change the coding table , use encoding
    x=f.readlines()
    for i in x:
        print(i,end="")

 function readline（）：

with open("lzs2.txt",'r')as f:
    x=f.readline()# Read the lines in the file ;（） The number in represents several numbers in the read line , When you enter a number , There is no blank line at the end , But the input number is not greater than the read size 
    print(x.strip()) #.strip  effect ： Put the last '\n' Delete   and end=""  equally , The two methods .

function readlines（）： Read multiple lines of the file at once ,

x=f.readlines()  # What is read out is a list 

with open("lzs2.txt",'r')as f:
    x=f.readlines()   # here x It's a list 
    for i in x: # It can be traversed （ Cyclic output ） it 
        print(i,end="")

Output results ：

12324543645247
1243253543
2143325
1312233421
43154

Format control ：

Format control can be performed during reading ;

Read the file （lzs2.txt） The content of

from datetime import datetime  The import module 
x="lzs2.txt"
with open("lzs2.txt",'r') as f:
    for i in f.readlines():
        mydate,price = i.split(',')#  Define assignment variables   use split With , Separate 
        # print(mydate,end=" ")
        # print(price)
        dt=datetime.strptime(mydate,"%Y/%m/%d") #strptime()  Function parses a time string into a time tuple according to the specified format 
        # print(dt)
        price=float(price) # There will be price Convert to floating point number , For appearance, there is a decimal point , Whether you actually turn it or not , because price The assigned value is the number 
        # print( dt,end=" ")
        # print(price)
        print(" Time is ：",str(dt.date())," sales ：",str(price))# Use here str Conversion because I converted , If it was not a string or a number , You need to turn 

Output results ：
Time is ： 2021-06-02 sales ： 1567.0
Time is ： 2021-06-03 sales ： 1244.0
Time is ： 2021-06-04 sales ： 4353.0
Time is ： 2021-06-05 sales ： 1324.0

Storage file ：

function write（）：
Write a character or a byte string

f.write(‘hello,world’)

x="lzs3.txt"
with open(x,'w',encoding="utf-8") as f: # If not before x This file , This step will directly generate a new file ,w Is write function 
    f.write(" This year will be a great year , Make a lot of money , Sure ！！") # Writing Chinese is not supported , There must be a step of code conversion ahead 

y="lzs4.txt"
with open(y,mode='r+',encoding="utf-8") as f:#r+  It's reading and writing , Overwrite from the original file ,w+ Is to empty the original file , Write from the beginning .
    f.write(" The family must be safe and happy ！！！")

function writelines( )
Used to write... To a file A sequence String or byte string of , A sequence can be a list 、 Tuples 、 Dictionaries 、 Collection etc. ;

writelines()

x=open("lzs.txt","r",encoding="utf-8")
y=open("./ New folder / new .txt","w",encoding="utf-8")
y.writelines(x.readlines())#  hold x Copy content from to y Inside , because y The original file already exists, so the y Directly replace the file in 
# therefore y Generally, it is an empty file , Or create a new file directly 
x.close()
y.close()# use open It must be opened with close shut;turn off 

Format control ：

from datetime import datetime
file = "file2.txt"
with open(file, 'w') as f:
	dt = datetime.strptime("2020/6/25", '%Y/%m/%d')  # Format and output the data 
	result=str(dt.date()) #
	f.write(result)