Python Learning Note Day3

1.set

Features: unordered and non-repeating collections

A. Create
Li = []    principle: List ((1,2,3,4))  list _init_ method, internal loop for loop (1,2,3,4)

Dictionary type definition: dict = {"K1": 123}
Set type definition: set = {"123", "456"}

B. function
Set ()

Create a Collection
LU = [1,2,1,2]
SS = Set (LU)
Print (ss)

Action Collection
Ss.add ()
Ss.clear ()
Ss.difference ()

2. Exercises:

What slots are added to remove updates

Old_dict = {
   "#1": 8,
   "#2": 4,
   "#4": 2,
}

New_dict = {
   "#1": 4,
   "#2": 4,
   "#3": 2,
}

3. Functions

function creation
Def f1 ():
     Aaa
     Bbb
     Ccc

1.def keywords
Name of 2.F1 function
3. ()
4. Function body

function immediately terminates when executing the return  function
Python default return value is None

function parameters
1. General parameters
2. The default parameter   must be placed at the end of the parameter list
3. Specifying parameters
4.*    receive dynamic Parameters   by default will be passed in the parameters, placed in tuples
5.**   Dictionary pass       -through defaults to the passed-in parameters, placed in the dictionary
6. Universal parameter  *args  **kwargs
7. Supplementary   reference  global variable with uppercase  read Assignment global  change the value dictionary list of global variables  within a function

4. Ternary operation

Basic structure: name = "Alex"  if 1 = 1 Else "SB"

Lambda expression

Built-in functions
ABS  Absolute
0,none, "", [], () A Boolean value of False
All ([1,2,3,4]) The all value within the all function is true all  is True
Any ([1,2,3,4]) in any function as long as one is true, any is true

ASCII ()
Bin (5)  decimal converted to 2 binary
Oct (9)  decimal converted to 8 binary
Hex (9)  decimal converted to 16 binary

Bytes string into bytes
s = "Chinese"
n = bytes (s,encoding= "Utf-8")
Print (n)

n = bytes (s,encoding= "GBK")
Print (n)

Bytes converted into strings
Str (bytes (s,encoding= "Utf-8"), encoding= "Utf-8")

5. File operation

1. Open File
f = open (' db ', ' R ')  read-only
f = open (' db ', ' W ')  write only
f = open (' db ', ' x ')  file exists error  does not exist create and write
f = open (' db ', ' a ')  append

f = open (' db ', ' RB ') operation mode plus b such as WB, RB, XB represent bytes directly operation

2. Operating files
F.seek (1)    byte method to locate the corresponding file location after overwriting
F.tell ()    gets the position of the current pointer
F.seek (F.tell ())
F.flush ()   Force write

For loop file Object f = open (XXX)
For line in F:
Print (line)

Python Learning Note Day3