Old boy Python Lesson notes

1. Development of Python

Python is Guido van Rossum (Guido van Rossum). During the Christmas of 1989, in Amsterdam to pass the time

Current Python main application areas:

• Cloud computing
• Web development:
• Scientific computing, artificial intelligence
• System operation and Maintenance
• Financial
• Graphical GUI

Python is an interpreted language

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.

Disadvantages:

1. Slow, Python is running slower than C and slower than Java.
2. The code cannot be encrypted, because Python is an explanatory language, and its source codes are stored in the form of a famous text.
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.

2. Python Version Classification     

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.

3. The encoding of Python 3 is Unicode

4. Variables    

Rules for variable definitions:

1. Variable names can only be any combination of letters, numbers, or underscores
2. The first character of a variable name cannot be a number
3. The following keywords cannot be declared as variable names
4. [' and ', ' as ', ' assert ', ' Break ', ' class ', ' Continue ', ' Def ', ' del ', ' elif ', ' Else ', ' except ', ' exec ', ' finally ', ' for ', ' F ' Rom ', ' Global ', ' if ', ' import ', ' in ', ' was ', ' lambda ', ' not ', ' or ', ' pass ', ' print ', ' raise ', ' return ', ' try ', ' while ', ' WI Th ', ' yield '

5. User input

Username = input ("Please enter user name:")

When entering a password, if you want to be invisible, you need to take advantage of the Getpass method in the Getpass module, the code sample is as follows:

#!/usr/bin/env python

  # -*- coding: utf-8 -*-   import getpass   # 将用户输入的内容赋值给 name 变量  Password  = getpass.getpass( "请输入密码：" )   # 打印输入的内容  print (Password)

Old boy Python Lesson notes