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This article mainly introduces "what are the new features of Python 3.9 version". In daily operation, I believe many people have doubts about what new features Python 3.9 version has. The editor consulted all kinds of materials and sorted out simple and easy-to-use operation methods. I hope it will be helpful to answer the doubts about "what new features Python 3.9 version has". Next, please follow the editor to study!

1. Dictionary merging

This is one of my favorite new features, and it has beautiful grammar. If you have two dictionaries an and b that need to be merged, you can use the merge operator:

Merge (merge) operator |:

A = {1: 'axed, 2:' baked, 3:'c'} b = {4: 'dumped, 5:' e'} c = a | b print (c) [Out]: {1: 'axed, 2:' baked, 3: 'cased, 4:' dumped, 5:'e'}

Update operator used to update the original dictionary | =:

A = {1: 'axed, 2:' baked, 3:'c'} b = {4: 'dumped, 5:' e'} a | = b print (a) [Out]: {1: 'axed, 2:' baked, 3: 'cased, 4:' dashed, 5:'e'}

If the dictionary shares a common key (common key), the key-value pair in the second dictionary is used:

A = {1: 'axed, 2:' baked, 3: 'caged, 6:' in both'} b = {4: 'but different',4, 5:' eBay, 6: 'but different'} print (a | b) [Out]: {1:' axed, 2: 'baked, 3:' cached, 6: 'but different',4:' dashed, 5:'e'}

Update the dictionary with iteration: the | = operator is also nice to be able to update the dictionary with new key-value pairs through iterable objects such as lists or generators.

A = {'averse:' one', 'baked:' two'} b = ((I, iatrophid2) for i in range (3)) a | = b print (a) [Out]: {'axed:' one', 'baked:' two', 0: 0, 1: 1, 2: 4}

If you try to use the standard merge operator | to do the same, a type error (TypeError) will be generated because it only allows merging between dictionary (dict) types.

two。 String method

This feature looks "unattractive", but it is actually very useful. The new version adds two new string methods for removing prefixes and suffixes:

"Hello world" .removeprefix ("He") [Out]: "llo world" Hello world ".removesuffix (" ld ") [Out]:" Hello wor "

3. New analyzer

This is an invisible change, but it has the potential to be one of the most important changes in the future development of Python.

Python currently uses mainly a syntax based on LL (1), which in turn can be parsed by a LL (1) parser, which uses a single forward marker to parse code from top to bottom and left to right.

I have little idea how it works, but I can point out some problems caused by Python's use of this method:

Python contains non-LL (1) syntax; some parts of the current syntax use workspaces, resulting in unnecessary complexity.

LL (1) places restrictions in the Python syntax (no workspaces are available). This problem highlights that the following code simply cannot be implemented using the current parser (raising a syntax error):

With (open ("a_really_long_foo") as foo, open ("a_really_long_bar") as bar): pass

The LL (1) recursively interrupts with the left in the parser. It means that a recursive syntax with a specific meaning can lead to an infinite loop in the parsing tree.

All these factors (and many others that are simply incomprehensible) seriously limit the development of the Python language. The new PEG-based parser will provide more flexibility for Python developers, as people will notice starting with Python 3.10.

4. Type hint

Python is dynamically typed, which means that there is no need to specify data types in your code. There is nothing wrong with this feature itself, but it can sometimes cause confusion.

Starting with Python 3.5, users can specify types, but it is very cumbersome to operate. This update changes that, for example:

No type hint (left) with type hint in vs3.9 (right)

The purpose of the add_int function is to add the same value to the value itself. But the editor doesn't know this, so you can use + to add two strings together without warning. You can now specify the desired input type as int. With this feature, the editor can immediately understand the problem.

Users can also learn about the types included in great detail, such as:

Type hints can be used anywhere, and the new syntax makes the code look cleaner:

Specify the parameter of sum_dict as dict and the return value as an integer. When defining a test, you also need to determine its type.

These new features are really impatient, and students who can't wait can try the latest version of Beta-3.9.0b3.

At this point, the study on "what are the new features of Python 3.9 version" is over. I hope to be able to solve your doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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