Shulou(Shulou.com)05/31 Report--

This article mainly introduces "what are the new functions of Python3.8 and how to use them". In the daily operation, I believe many people have doubts about what the new functions of Python3.8 are and how to use them. The editor consulted all kinds of materials and sorted out simple and easy-to-use methods of operation. I hope it will be helpful to answer the doubts about "what are the new functions of Python3.8 and how to use them?" Next, please follow the editor to study!

1. Assignment expression

The most obvious change in Python 3.8 is the assignment expression, that is, the = operator. An assignment expression can assign a value to a variable, even if the variable does not exist. It can be used in expressions without having to appear as a separate statement.

While (line: = file.readline ())! = "end": print (chunk) "end": print (chunk)

In the above example, if the variable line does not exist, it is created and the return value of file.readline () is assigned to it. Then check to see if line is "end". If not, read the next line, save it in line, and continue testing.

Assignment expressions follow Python's tradition of simplicity, just like list parsers. The goal is to avoid some boring boilerplate code in a particular Python programming mode. For example, the general way to write the above code requires two more lines of code.

2. Only the parameters specified by location

A parameter specified only by position is a new syntax in the function definition that allows the programmer to force a parameter to be specified only by location. This can solve the ambiguity of which parameter is the position parameter and which parameter is the key parameter in the Python function definition.

Parameters specified only by location can be used in situations where a function accepts any keyword parameter, but can also accept one or more unknown parameters. This is usually the case with Python's built-in functions, so allowing programmers to do so enhances the consistency of the Python language.

The examples given in the Python documentation are as follows:

Def pow (x, y, z=None, /): r = x if z is not None: r% = z return r r = x if z is not None: r% = z return r

The symbol / separates the position parameter and the keyword parameter. In this example, all parameters are unknown. In previous versions of Python, z would have been considered a keyword parameter. However, using the above function definition, pow (2, 10) and pow (2, 10, 5) are both correct methods of calling, while pow (2, 10, zonal 5) is incorrect.

3. Support f string debugging

F string format makes it easier to evaluate output text and values or variables within the same expression, and is more efficient.

X = 3 print (f'{xylene 1}') print (f'{xylene 1}')

Output 4.

If you don't add = at the end of the f string expression, you can output the value of the f expression itself, followed by the calculated value

X = 3print (f' {xylene 1 =}') print (f'{xylene 1 =}')

The output is xdye 1x 4.

4. Multi-process shared memory

In Python 3.8, the multiprocessing module provides the SharedMemory class to create shared memory areas between different Python trips.

In the old version of Python, data shared between processes could only be written to a file, sent through a network socket, or serialized using Python's pickle module. Shared memory provides a faster way to transfer data between processes, which makes Python's multiprocessor and multi-core programming more efficient.

Shared memory fragments can be allocated as simple byte areas or as immutable list-like objects, in which a small number of Python objects such as numeric types, strings, byte objects, None objects, and so on can be saved.

5. Improvement of Typing module.

Python is a dynamically typed language, but you can add type hints through the typing module so that third-party tools can validate Python code. Python 3.8 adds some new elements to typing, so it can support more robust checks:

Final modifiers and Final type annotations indicate that objects that are modified or annotated should not be overridden, inherited, or reassigned at any time.

The Literal type restricts an expression to a specific value or list of values (not necessarily values of the same type).

TypedDict can be used to create dictionaries whose specific key values are limited to one or more types. Note that these restrictions are used only to determine the validity of values at compile time, not at run time.

6. New version of pickle protocol

Python's pickle module provides a way to serialize and deserialize Python data structures or instances, saving the dictionary as it is for later reading. Different versions of Python support different pickle protocols, while the latest version supports broader, more powerful, and more efficient serialization.

The version 5 pickle protocol introduced by Python 3.8 can use a new method, pickle object, which can support Python's buffer protocol, such as bytes, memoryviews, Numpy array, etc. The new pickle avoids many of the memory copy operations when pickle these objects.

External libraries such as NumPy and Apache Arrow support the new pickle protocol in their Python bindings. The new pickle can also be used as a plug-in for Python 3.6and 3.7and can be installed from PyPI.

7. Invertible dictionary

The dictionary has been rewritten in Python3.6, which uses a new implementation of the PyPy project contribution. In addition to being faster and more compact, today's dictionaries inherit the order of elements-elements are arranged in the order in which they are added, just like lists. Python 3.8also allows the use of reversed () in dictionaries.

8. Performance improvement

The speed of many built-in methods and functions has been increased by 20% to 50%, because many previous functions require unnecessary parameter conversions.

A new opcode cache can increase the speed of specific instructions in the interpreter. But LOAD_GLOBAL opcode is the only one that has achieved a speed improvement of 40 per cent. Similar optimizations will be made in future releases.

File copy operations such as shutil.copyfile () and shutil.copytree () now use platform-specific calls and other optimizations to speed up operations.

The newly created columns are on average 12% smaller than before, thanks to optimizations made by the list constructor if the list length is known in advance.

Writes to class variables of new classes, such as class A (object), become faster in Python 3.8. Operator.itemgetter () and collections.namedtuple () also get speed optimizations.

9. Python C API and CPython implementation

Recent versions of Python have put a lot of effort into C API refactoring used in CPython. So far, these efforts have been continuously added, and the existing achievements include:

Python initialization configuration (Python Initialization Configuration) has a new C API that enables tighter control and more detailed feedback on Python initialization routines. This makes it easier to embed the Python runtime in other applications, and you can programmatically pass startup parameters to Python programs. The new API also ensures that all Python configuration controls have a single, consistent location, making it easier to change later (such as Python's new UTF-8 mode).

Another new C API-- "vectorcall" invocation protocol for CPython enables faster calls to Python internal methods without creating temporary objects. The API is still unstable, but it has improved significantly. The API program matured in Python 3.9.

The audit hook of the Python runtime provides the Python runtime with two API that can be used to trap events, ensuring that external tools such as the test framework, logs, and audit systems can monitor them.

At this point, the study on "what are the new features of Python3.8 and how to use them" 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!

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.