Getting started with python, python

Getting started with python, python

Python type

Cpython: parses the python code into pyc (python bytecode) using the C language, and then runs it on the python Virtual Machine (the PYTHON we learn is cpython)

Jpython: parses the python code into a java bytecode using the java language, and then runs on the jvm (java Virtual Machine ).

Pypy: Use python to implement python, compile python byte friends into machine code, and then run

 

Code running principle

Process: 1. First, dynamically compile the source code into bytecode 2. Then, compile the bytecode into a machine code through the corresponding virtual machine, and then interact with the CPU Instruction Set for execution.

 

First python Program

[Root @ localhost day1] # cat first. py #! /Usr/bin/env python3 # specify the python interpreter #-*-coding: UTF-8-*-# specify the encoding format print ('Hello world! ') [Root @ localhost day1] # alias pyalias py = 'python3' [root @ localhost day1] # py first. pyhello world!

 

Encoding format

Ascii: The computer content is expressed in 1 byte, that is, it has only eight digits and can contain a maximum of 256 characters. It is enough for English letters, however, other non-English languages show their limitations. Therefore, unicode occurs.

Unicode: a universal code, a single code, is generated to address the limitations of traditional character encoding. It sets a unified and unique binary code for each character in each language, at least two bytes are used for representation.

UTF-8: compresses and optimizes unicode and classifies characters and symbols. For example, ascii occupies one byte and European characters occupies two bytes, asian characters occupy 3 bytes (this encoding format is often used for writing code)

 

Input parameters when executing the script

Python provides the sys module to implement this function. The example is as follows:

[root@localhost day1]# cat args.py#!/usr/bin/env python3import sysprint(sys.argv)[root@localhost day1]# py args.py['args.py'][root@localhost day1]# py args.py arg1 arg2['args.py', 'arg1', 'arg2']

 

Variable

String: single quotation marks, double quotation marks, and three quotation marks (multiple rows). Once defined, a memory space is opened up.

Example: str1 = 'a'; str2 = "aa"; str3 = "" aa \ nbb \ ncc """

Number: integer 32/64 long integer (unlimited length), floating point type, plural

List: An Array

Example: list1 = ['A', 'B', 1]

Tuple: a list that cannot be modified. For example, the week and month are represented by tuples.

Example: tuple1 = ('mon', 'tus ', 'thir',) tuple2 = 1, 2, 3

Dictionary (dict): it may be roughly understood as a key-Value Pair (hash)

Example: dict1 = {'name': 'hoho', 'age': 18}

 

Boolean value: true or false, 1 or 0

Operator

Arithmetic Operation: +-*/** // %

Logical operation: and or not

Member operations: in, not in

Comparison calculation: ><>==! = <>

Identity calculation: is, is not

Value assignment: = + =-= * =/= % = ** =

Bit operation: & | ^ ~ >>< (Rarely used)

 

Process Control

1. Conditional Control (the statement blocks under elif can be omitted, depending on the situation)

If con:

Pass

Elif con2:

Pass

Else:

Pass

 

2. Loop Control

2.1 while Loop

While con:

Pass

2.2 for Loop

For I in list/iter:

Do somethings ..