Python 3.9 is coming... Exciting time

ztenv 2020-11-13 12:59:55
python coming... coming exciting time


This paper mainly introduces Python3.9 Some new features of , Such as : Faster process releases , Performance improvement , Simple new string function , Dictionary union operator and more stable internal API, Detailed as follows :

  • Dictionary Union and iterative update

  • String method

  • Type tips

  • New mathematical functions

  • The new parser

  • IPv6 Address in range

  • New modules : Regional information

  • Other language changes

1、 Dictionary Union and iterative update

          Python 3.9 dict class . If there are two dictionaries a and b, You can now use these operators to merge and update .

We have merge operators |:

                               

Use Iterables Update dictionary

| = Another great performance of the operator is the ability to use iteratable objects ( Such as lists or generators ) Update the dictionary with new key value pairs :

a = {'a': 'one', 'b': 'two'}
b = ((i, i**2) for i in range(3))
a |= b
print(a)
{'a': 'one', 'b': 'two', 0: 0, 1: 1, 2: 4}

2、 String method

removeprefix() and removesuffix()

str.removeprefix(substring:string) String method : If str If you start with it , Will return a new string with modified prefix , Otherwise, it will return the original string .

str.removesuffix(substring:string) String method : If str End with it , Returns a new string with a modified suffix , Otherwise, it will return the original string .

                                  

The operations performed by these two functions will use string [len(prefix):] As a prefix ,string [:-len(suffix)] As a suffix .

These are very simple operations , So it's also a very simple function , But considering that these operations may be performed frequently , It's better to have a built-in function to do this .

3、 Type tips

Python Is dynamic , Dynamically assign data types to variables , That means we don't have to specify the data type in the code .

But sometimes it can cause confusion !

For static allocation of data types , Type hints are usually used . This is Python 3.5 Introduced in . from 3.5 Start , We can specify the type , But this is more troublesome .

This update really changed that , Now you can set the built-in collection type (List and Dict) Used as a generic type .

Before , The uppercase type must be called by input List and Dict.


ef greet_all(names: list[str]) -> None:
for name in names:
print("Hello", name)

Now? , No need to typing.List To call List

4、 New mathematical functions

The math module adds and improves many auxiliary functions , Start with improvements to existing features .

 

import math#Greatest common divisormath.gcd(80, 64, 152)#8

Previously used to calculate the greatest common factor gcd Function can only be applied to 2 A digital , Forcing programmers to do something like math.gcd(80,math.gcd(64,152)) The operation of . from Python 3.9 Start , We can apply it to any number of values .

math The first new addition to the module is math.lcm function :

#Least common multiple
math.lcm(4, 8, 5)
#40

math.lcm Calculate the least common multiple of its parameters . And GCD equally , It allows a variable number of parameters .

5、 The new parser

This part is more of a change out of sight , But it could be Python One of the most significant changes in the future .

Python 3.9 A new one based on PEG The parser . before Python Use LL(1), When building new features of the language ,PEG Than LL(1) More flexible . Official documents say , This flexibility will be in Python 3.10 And later .

ast The module uses a new parser , And produce the same as the old parser AST.

6、IPv6 Address in range

Python 3.9 The other One change is You can specify IPv6 Address range .IPv6 The scope is used to specify the corresponding IP The address in Internet Which part of is effective .

Scope can be used % The sign is in IP The end of the address specifies —— for example :3FFE:0:0:1:200:F8FF:FE75:50DF%2—— So it's time to IP The address is in the range 2 in , Link to local address .

therefore , If needed Python Handle IPv6 Address , Now you can do this :

from ipaddress import IPv6Address
addr = IPv6Address('ff02::fa51%1')
print(addr.scope_id)
#"1" - interface-local IP address

7、 New modules : Regional information

Regional information

zoneinfo The module will IANA The support of time zone database is introduced into standard database . It adds zoneinfo.ZoneInfo, This is a specific datetime.tzinfo Realization .

                                

8、 Other language changes

__import __() Now it's added ImportError To replace ValueError, Usually occurs when a relative Import exceeds its top-level package .

“” .replace(“”,s,n) Now for all nonzero n return s Instead of empty strings . Now it's with ““ .replace(”“,s) Consistent .

By default ,Python Faster and faster

Python Each revision of has performance improvements compared to previous versions of .Python 3.9 Two major improvements have been made , Performance can be improved without any changes to existing code .

The first is more about the use of vector call protocols , Many common function calls are made by minimizing or eliminating temporary objects .Python 3.9 Several new built-in functions have been introduced , Include range、tuple、set、frozenset、list、dict —— Use vectorcall Can speed up execution .

Python Switch to annual release cycle

up to now ,Python Have already used 18 Months of development and release .PEP 602 proposal Python The development team uses an annual release cycle , And the proposal has been accepted .

 

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