Python road Day06

Small data pool

• == determines two values ​​are equal

• It is - is determined on both sides of the same memory address

  • a=10
    b=10
    print(a is b)

• id () - View the memory address

Block

• Py a file, a function, a module, each row is the terminal block

  • int，str，bool

  • int: -5 ~ + infinity

    • a=1000
      b=1000
      print(id(a)，id(b))
      print(a,b)

  • str:

    • Defined string can be arbitrary,
    • Character string (letters, numbers) for multiplying the length of the string can not exceed 20
      • Python3.7 above version is <= 4096
    • You can only take the 1:00 special symbols (Chinese symbol) to multiply or multiply 0

  • bool

    • True
    • False

• Case of a small data pool with the same code block in the first block of code

• Resident mechanism: save memory space, improve efficiency (reduce the destruction of open space and space-consuming)

Small data pool

• int，str，bool
  • int：-5~256
  • str：
    • Supports only letters, numbers; any length compliance mechanism residing
    • When multiplying the total length of the string can not exceed 20
    • Special symbols can only multiply when the multiplication 0

Copy depth

1. After avoided
2. The interview will ask

Assignment

• a=[1,2,3,4]
  b=a
  print(id(a),id(b))

Shallow copy

• Assignment: a plurality of variable names point to the same memory address

• copy - copy

• (Case is open, the same Nang)

  • a=[1,2,3,4,5]
    b=a.copy()
    print(id(a[0]))
    print(id(b[0]))

  • a=[1,2,3,4,5]
    b=a[:]      #切片  浅拷贝
    print(id(a[-1][0]))
    print(id(b[-1])[0])

  • a=[1,2,3,[4,5]]
    b=a[:]
    

• Shallow copy

  • Copy only of the first layer element address, modifying the first layer is modified only when the source data is not changed
  • When added to the variable data source data types affected
    • Variable data types can be modified to add, modify only immutable type

Deep copy

• import copy - the copy module introduced

• import copy
  a=[1,2,3,[4,5],6]
  b=copy.deepcopy(a)

• Deep copy: common immutable data types, data type of the variable to open a new space (either how to change one of the other does not change)

set

• One data type Python, disorder, variable, natural deduplication
• Collection - set
  • s=set(): Empty set
  • Dictionary is a collection of no value (element unique, immutable)

Collection method

increase

• s.add()
• s, update ( 'alex) - recursive addition
  • print (set ( 'alex')) - recursive addition

delete

• s.remove () - deleted by elements
• s.clear () - Clear
• s.pop () - random deletion (minimum)

change

• After the first cut plus

check

• for loop

Other operations

• Subtraction: Difference Sets
• &: Intersection
• | (Pipe symbol): union
• ^: Anti intersection
• >:判断是否子集
• print(frozenset({1,2,3,4}))Freeze collection (the collection of immutable)