python-7- encapsulation and deconstruction

Encapsulation and deconstruction

• Package
  • Separate multiple values ​​with commas and combine them
  • Essentially, return a tuple, but omit the parentheses
  • Python unique grammar, learn and learn from many languages ​​# For example ES6
  • t1 = (1,2) # defined as tuple
  • t2 = 1,2 # Pack 1 and 2 into tuples
  • type(t1)
  • type(t2)

Tuples are simpler than lists, and are lighter than lists in memory, so the list is closed

• Examples

a = 4
b = 5
temp = a
a = b
b = temp
a,b=b,a 
# 上面语句当中，等号右边使用了封装，而左边就使用了解构

Deconstruction

• Untie the elements of the linear structure and assign them to other variables in sequence

• The number of variables accepted on the left must be the same as the number of elements unwrapped on the right

• Examples

  • lst=[3,5]
  • first,second=lst
  • print(first,second)

• Examples

a,b=1,2
a,b=(1,2)
a,b=[1,2]
a,b=[10.20]
a,b={10.20}
a,b=('a':10,'b':20) # 非线性结构也可以解构
a,b={10,20,30}
a,*b={10,20,30}
[a,b]=(1,2)
[a,b]=10,20
(a,b)={30,40}

python3 deconstruction

• Use *变量名receiving, but can't use alone
• After being *变量名collected, make up a list
• Examples
  • lst=list(range(1,101,2))
  • head,*mid,tail=lst
  • *lst2 = lst
  • *body,tail=lst
  • head,*tail=lst
  • head,*m1,*m2,tail=lst
  • head,*mid,tail=*abcdefghijklmn
  • type(mid)

Discard variables

• This is a convention, an unwritten agreement, not a standard
• If you don't care about a variable, you can define the variable name as_
• _It is a legal identifier and can also be used as a valid variable.
• But defined as an underscore is to hope that it will not be used unless you clearly know that this data needs to be used
• Examples
  • lst=[9,8,7,20]
  • first,*second=lst
  • head,*_,tail=lst
  • print(head)
  • print(tail)
  • #_It is a legal identifier. You will know that this variable just doesn't want to be used when you see the underline
  • print(_)

lst=[9,8,7,20]
first,*second=lst
_,*_,tail=lst
print(_)
print(tail)
print(_)

• to sum up
  • _This variable itself has no semantics and no readability, so it is not intended for human use.
  • Many libraries in Python use this variable, which is very widely used,
  • Please do not _cause _conflicts with the library without specifying the scope of the variable
• Exercise
  • lst = list (range (10)) # Such a list, take out the second, fourth, second to last

Exercise

• From lst=[1,(2,3,4),5]extracted out 4
• Environment variable JAVA_HOME=/usr/bin, return variable name and path
• [1,9,8,5,6,7,4,3,2]Use the bubble method to sort the list , requiring the use of encapsulation and structure to interact with the data

lst=[1,(2,3,4),5]
a,(b,c,d),e=lst
print(a,b,c,d,e)

_,(*_,val),*_=lst
print(val)

_,[*_,val],*_=lst
print(val)

key,_,val='JAVA_HOME=/usr/bin'.partition('=')
print(key)
print(val)

• to sum up
  • Deconstruction is a good function provided by Python, which can easily extract the value of complex data structures
  • With _the use of it, it will be more convenient!