Python Foundation Week01

Tag: The main thread updates its market by default and causes the wiki to compile the run environment

The compiler compiles each statement of the source program into a machine language and saves it as a binary file so that the computer can run the program directly in machine language at a very fast speed.

And the interpreter is only in the execution of the program, only one interpretation of the machine language to the computer to execute, so the speed is not as fast as the compiled program to run.

This is because the computer does not directly recognize and execute the statements we write, it only knows the machine language (in binary form)

(2). Compiled vs explanatory type

　　 Compiled type: 　　 Advantages: The compiler typically has pre-compiled procedures to optimize the code. Because the compilation is done only once, the runtime does not need to compile, so the program execution of the compiled language is highly efficient. Can run independently from the language environment. Cons : After compilation, the entire module needs to be recompiled if modifications are required. When compiling the machine code according to the corresponding running environment, porting between different operating systems will be problematic, and you need to compile different executables according to the operating system environment you are running.

Explanatory type:

　　Pros: Good platform compatibility, can be run in any environment, provided the interpreter (virtual machine) is installed. Flexible, modify the code when the direct modification can be quickly deployed, without downtime maintenance.

　　cons : Every time you run, you have to explain it again, performance is not as good as the compiled language.

(3). Python pros and cons

First look at the advantages:

1. Python's positioning is "elegant", "clear", "simple", so the Python program looks always easy to understand, beginners learn python, not only easy to get started, but also in the future, you can write those very very complex programs.
2. Development efficiency is very high, Python has a very powerful third-party library, basically you want to achieve any function through the computer, the Python official library has the corresponding modules to support, directly download the call, on the basis of the base library to develop, greatly reduce the development cycle, to avoid repeating the wheel.
3. High-level language ———— when you write programs in the Python language, you don't have to consider the underlying details such as how to manage the memory used by your program
4. Portability ———— because of its open source nature, Python has been ported on many platforms (modified to make it work on different platforms). If you are careful to avoid using system-dependent features, all your Python programs can run on almost any system platform on the market without modification
5. Scalability ———— If you need a piece of your critical code to run faster or you want some algorithms to be private, you can write some of your programs in C or C + + and then use them in your Python program.
6. Embeddable ———— You can embed python into your C + + program to provide scripting functionality to your program users.

Look at the disadvantages again:

1. Slow, Python runs faster than the C language, and slower than Java, so this is the main reason why many so-called Daniel disdain to use Python, but in fact, this refers to the speed of slow in most cases the user is not directly aware of, Must rely on the use of testing tools to reflect, such as you use C a program to spend 0.01s, Python is 0.1s, so c directly than Python 10 times times faster, is very exaggerated, but you can not directly perceive through the naked eye, Because a normal person can perceive the smallest unit of time is 0.15-0.4s around, haha. In fact, in most cases python has been fully able to meet your requirements for the speed of the program, unless you want to write to the speed of the most demanding search engine, in this case, of course, it is recommended that you use C to achieve.
2. Code can not be encrypted, because Python is an explanatory language, its source code is stored in the form of a name, but I do not think this is a disadvantage, if your project requires that the source codes must be encrypted, then you should not use Python in the beginning to implement.
3. Threads do not take advantage of multi-CPU problems, which is one of the most common drawbacks of Python, the Gil, the Global Interpreter lock (interpreter lock), is a tool that the computer programming language interpreter uses to synchronize threads so that only one thread executes at any moment, The python thread is the native thread of the operating system. On Linux for Pthread, on Windows for win thread, the execution of threads is fully dispatched by the operating system. A Python interpreter process has a main thread and the execution thread for multiple user programs. Multi-threaded parallel execution is prohibited even on multicore CPU platforms due to the existence of the Gil. A compromise solution to this problem is discussed in more detail later in the Threads and Processes section.

(4). Introduction to the Python interpreter

When we write the Python code, we get a text file that contains the Python code for the .py extension. To run the code, you need the Python interpreter to execute the .py file.

Since the entire Python language is open source from spec to interpreter, it is theoretically possible for anyone to write a Python interpreter to execute Python code (which is difficult, of course) as long as the level is high enough. In fact, there are a number of Python interpreters.

CPython

When we downloaded and installed Python 2.7 from the official Python website, we immediately got an official version of the interpreter: CPython. This interpreter was developed in C language, so called CPython. Running at the command line python is to start the CPython interpreter.

CPython is the most widely used Python interpreter. All the code for the tutorial is also executed under CPython.

IPython

Ipython is an interactive interpreter based on CPython, meaning that Ipython is only enhanced interactively, but the functionality and CPython of executing Python code are exactly the same. Like many domestic browsers although the appearance of different, but the kernel is actually called ie.

CPython >>> is used as a prompt, while Ipython is used In [ 序号 ]: as a prompt.

PyPy

PyPy is another Python interpreter whose goal is to perform speed. PyPy uses JIT technology to dynamically compile Python code (note that it is not interpreted), so it can significantly improve the execution speed of Python code.

Most python code can run under PyPy, but PyPy and CPython are somewhat different, which results in the same Python code being executed under both interpreters. If your code is to be executed under PyPy, you need to understand the differences between PyPy and CPython.

Jython

Jython is a Python interpreter running on the Java platform that compiles python code directly to Java bytecode execution.

IronPython

IronPython is similar to Jython, except that IronPython is a Python interpreter running on the Microsoft. NET platform that compiles python code directly into. NET bytecode.

Iii. Choose py2.x or py3.x?

Most of the current Python programs are based on py2.7+ above, but it is advisable to learn python from py3.x, and to understand the difference between py2.x and py.3.x. and promote the use of py2.x to py3.x!

Four. Python installation

1): Windows installation

　　　　1、下载安装包

    　　 https: / / www.python.org / downloads / 　　　　2 、安装     　　 默认安装路径：C:\python27 　　　　3 、配置环境变量     　　 【右键计算机】 - - 》【属性】 - - 》【高级系统设置】 - - 》【高级】 - - 》【环境变量】 - - 》【在第二个内容框中找到 变量名为Path 的一行，双击】  - - > 　　　　【Python安装目录追加到变值值中，用 ； 分割】      如：原来的值;C:\python27，切记前面有分号

2): Linux/mac installation

　　　　无需安装，原装Python环境

  　　　　ps：如果自带 2.7 ，请更新至3.x
..... Continued update

Python Foundation Week01