Python 0 Basic Learning-Fundamentals 5-Collections and files

Collection: a special list

• The data in the collection is not duplicated
• You can test the relationship between two sets of data: intersection, set, and difference set
• The data in the collection is unordered

1. Create a Collection

# ---------------------------Method 1---------------------list1=[1,2,3,4,5]list2=Set (list1)  Print(list2)         # Execution Result: {1, 2, 3, 4, 5}, curly brace is the identity of the collection print(Type (LIST2))   # execution Result: <class ' Set ' > # --------------------------Method 2-----------------------List3=set ([2, 4, 6, 8, 10])

2. Set Relationship Test

1) Seek the intersection

Print (List2.intersection (LIST3)) Print (list2&list3) # Execution Result: {2, 4}

2) Seek and remove weight

Print (List2.union (LIST3)) Print (list2| list3) # execution Results: {1, 2, 3, 4, 5, 6, 8, ten}

3) Differential set: 1 have, 2 no

Print (List2.difference (LIST3)) Print (list2-list3) # Execution Result: {1, 3, 5}

4) Symmetric difference set: set-intersection

Print (List2.symmetric_difference (LIST3)) Print (list2^list3) # Execution Result: {1, 3, 5, 6, 8, ten}

5) Relationship Judgment

Print (List2.issubset (LIST3), List2.issuperset (LIST3)) # Determines whether List2 is a subset of LIST3; Determines whether List2 is the parent set of List3 # execution Result: false false Print (List2.isdisjoint (LIST3)) # two set without intersection returns TRUE, otherwise false

3. Changes to the collection

List2.add (+)                     # Add a item in the collection #  list2.remove (104)                  #  Removes an item in the collection List2.pop ()                        # arbitrarily deletes an item list2.discard (103)                 # exists then deletes, does not exist then ignores 

TIP:

The following methods determine whether an element exists, for dictionaries, lists, collections, strings

Print  in List2)              # returns TRUE or false

File

1. Open the file and read the contents of the file

#Method 1Data=open ("file1", encoding="Utf-8"). Read ()#If you do not label the encoding format, it will be opened using the operating system default encoding. Windows default encoding format is GBKPrint(data)#Print the entire contents of a file#method 2; To avoid constantly invoking the open method to create a file object, use Method 2 as much as possibleF=open ("file1", encoding="Utf-8")#To create a file handleData=F.read ()Print(data)#Print the entire contents of a filedata1=F.read ()Print(DATA1)#print empty. Reason: When reading data, the cursor of the file has been moved to the bottom of the fileF.close ()

2. File read and write mode

1) W: write mode, cannot read file

F=open ("file2","w", encoding="utf-8  ")           # Create a new file file2; If the file already exists, it will overwrite the previous f.write (" la la la, I'm a little connoisseur of the newspaper")      #  Write content to the newly created file f.close ()

2) A: Append mode, cannot read file

F=open ("file2","a", encoding="utf-8             # # # # # Open an existing File2 file f.write (" go to the morning and sell the newspaper \ \ \ \ \ \" run and call \ \")        # Append the content to the end of the file F.close ()

3) R: Read-only mode, only read files, cannot write; If read-write mode is not specified, the default is R

#reads the contents of the file as a list, one element for each behavior, and the method consumes a lot of memory and tries not to useF=open ("file1","R", encoding="Utf-8")Print(F.readlines ()) F.close ()#Loop ReadF=open ("file1","R", encoding="Utf-8") forIinchRange (5):    Print(F.readline ()) F.close ()#the most efficient method, the recommended useF=open ("file1","R", encoding="Utf-8") forLineinchF:Print(line) f.close ()

4) r+: Can read the file, can be written in an append way

F=open ("file2","r+", encoding="utf-8 " )print(F.readline ())                        # can read the file f.write (" today's news really good \ n  ")             # starts writing the file from the last side of the file, writes it as an append, and moves the cursor without f.close ()

5) w+: First create a new file, then write

F=open ("file1","w+", encoding="utf-8 " f.write (" la la la, I'm a little connoisseur of the newspaper, not till Dawn to sell the newspaper ") F.seek (6) F.write (  "123")      # will start writing from where the cursor is, but will be written in insert mode, overwriting the following characters F.close ()

6) RB:

• Read files in binary format
• Cannot specify encoding parameters, usually used for network transmission, video files, file cross-platform open and other functions

7) WB: must be converted into binary encoding for writing

3. File Handle Location

F=open ("file1","R", encoding="Utf-8")Print(F.tell ())#Print file handle position, initial position is 0F.readline ()Print(F.tell ())#The handle reaches the second line, and in this example the value is---> The number of characters in the first row of charactersPrint(F.read (2))#start at a subordinate, read two charactersf.seek (0)#Handle Returns the beginning of the filef.close ()

4. Modification: There are only two ways

• Load all into memory, write it after the modification is complete
• Read it, change it, save it in a new file.

F=open ("file2","R", encoding="Utf-8") F_new=open ("File3","W", encoding="Utf-8") forLineinchF:if "reported" inchLine:line=line.replace ("reported","Newspapers") F_new.write (line) F.close () f_new.close ()

5. Other

Print(f.encoding)#Print File EncodingPrint(F.name)#Print file nameF.truncate ()#empty the file, erase it from the beginning, and move the cursor without using#F.flush (): Forces the contents of memory to be flushed to the hard disk, often for write-sensitive data such as amounts#when a refresh is not enforced, the system waits for a certain amount of data to be written to the hard disk when the memory is stored#Simulation Process BarImportSys, time forIinchRange (20): Sys.stdout.write (">") Sys.stdout.flush () Time.sleep (0.5)

6. With statement: The file is automatically closed after execution is complete

With open ("file2","R", encoding="Utf-8") as F:Print(F.readline ()) with open ("file2","R", encoding="Utf-8") as F1,open ("File3","R", encoding="Utf-8") as F2:Print(F1.readline ())Print(F2.readline ())

Python 0 Basic Learning-Fundamentals 5-Collections and files