Python three-day simple learning Day1

First, Python overview:

(a), Python introduction:

1.python Origin:

Guido van Rossum, a Python rosam, was founded at the end of 1989.

In early 1991, Python released its first public release

A research project for the purpose of its creation in order to better complete the CWI (National Institute for Mathematics and Computer science) in the Netherlands

Features of 2.python:

Advanced: Advanced data structure to shorten development time and code volume

Object-oriented: Adds new vitality to structured and procedural programming that separates data and logic

Upgradeable: Provides a basic development module that can be used to develop software for code reuse

Extensible: Organize management by separating it into multiple files or modules

Portability: Python is written in C and, because of the portability of C, Python can run on any platform with an ANSI C compiler

Easy to learn: Python has fewer keywords, simple structure and clear syntax

Easy to read: No other language is commonly used to access variables, define blocks of code, and perform pattern-matching imperative symbols

Memory Manager: The memory manager is the responsibility of the Python interpreter

Second, Python start:

(a), Python syntax structure:

1. Statement block indentation:

The Python code block expresses the code logic with indentation alignment instead of curly braces

2. Program output:

Print prints data to the screen

print ' Hello World '--->Hello World

3. Program Input:

Use the Raw_input () function to read user input data

4. Notes:

Use the # symbol to mark comments

5. Document string:

Can be used as a special note, a simple description using single or double cited, a longer description using the three-lead

Quotation marks: Single-lead, double-lead, three-lead

Single citation '

Double citation ""

Three-lead "or" "" "" can be wrapped.

(ii), Python variables:

1. Variable definition:

1). Variable Name conventions:

Use alphanumeric underscores, starting with letters or underscores

Note: Python is a dynamic type language, that is, you do not need to declare the type of a variable beforehand

2). Variable assignment:

The type and value of the variable are initialized at the moment of assignment.

Variable assignment is performed by an equal sign, and Python also supports incremental assignment

3). Operator:

Standard operators:

+ - * / // % **

Comparison operators:

> >= = = = <= < ps: No matter numbers or letters

Logical operators:

And not OR

Iii. python data type: (type () query data type)

(a), number:

1. Basic Number types:

int by signed integer

Long Integer

BOOL Boolean value

float floating point number

Complex plural

2. Digital representation:

The number is used by default in decimal:

Numbers start with 0 to indicate 8 binary numbers (more important)

Numbers start with a 0x or 0X representation of 16 binary

Numbers start with 0b or 0 B to indicate 2 binary

#################################

#修改文件权限 (using 8 binary)

Import OS

Os.chmod (' Test.txt ', 00644)

#################################

(b), string:

1. Define the string:

Pyhton strings are defined as character sets between quotes, Python does not differentiate between characters and strings

2. String slices:

Use the index operator [] and the slice operator [:] to get substrings

The index of the first character is 0, and the index of the last character is-1

The substring contains the starting subscript in the slice, but does not contain the end subscript

#################################

#对字符串切片

Py= ' 0123456789abcdef '

Print Py[1:4]

1234//starting from 0, not including fourth digit

Print Py[5:]

56789abcdef//starting from 5th to last

Print Py[:5]

01234 //from No. 0 place to 5th position, excluding 5th digit

#################################

3. String continuous operation:

Multiple strings can be stitched together using the + sign

Use the * number to repeat a string multiple times

(c), list: (a variable to store multiple values) []

1. Define the list:

You can use a list as a normal "array" to hold any number of arbitrary types of Python objects

The list also supports subscript and slice operations, where items can be changed

2. List operations:

Use in or not to determine a member relationship

To append an element to the list using the Append method

#################################

A=[11,22,33]

Print a--->[11, 22, 33]

Print a[0]--->11

Print a[1]--->22

Print a[2]--->33

Print A[0:2] --->[11, 22]

a[0]==99

Print a--->[99, 22, 33]

A.append ()//use in or not to determine member relationships

Print a--->[11, 22, 33, 44]

Print in a--->True//Append elements to the list

#################################

(iv), tuple: (a variable to store multiple values) ()

1. Definition and operation of the tuple:

You can think of tuples as a "static" list, and once a tuple is defined successfully, you cannot modify

#################################

A= (11,22,33)

Print a[0]--->11

#################################

(v), Dictionary: (one variable to store multiple values) {}

1. Definition and operation of the dictionary:

A dictionary is a mapping data type consisting of a key-value (Key-value), which is not supported by key values.

#################################

a={' l ': ' X ', ' m ': ' Y ', ' n ': ' Z '}

Print a[' l ']--->x

a[' l ']= ' m '

a[' P ']= ' n '

Print a---> {' P ': ' N ', ' m ': ' Y ', ' l ': ' m ', ' n ': ' Z '}

#################################

(vi), data type comparison:

1. Classify by Storage model:

Scalar types: Numbers, strings

Container type: list, tuple, dictionary

2. Classification by Update Model:

Mutable type: list, dictionary

Immutable types: Numbers, strings, tuples

3. Classification by Access model:

Direct access: Digital

Sequential access: strings, lists, tuples

Map Access: Dictionaries

Iv. Judgment statement:

(a), if statement:

1.if statement Syntax structure:

Syntax for standard if condition statements:

If expression:

If_suite

Else

Else_suite

If the value of the expression is not 0 or a Boolean value of True, the code group If_suite, otherwise execution else_suite

2.if Statement Example parsing:

True if the expression number is a value other than 0

The values for empty strings, empty lists, empty tuples, and empty dictionaries are all flase

(b), extend the IF statement:

1. Extend the IF statement structure:

1). Expand the syntax of the IF condition statement:

If expression1:

If_suite

Elif expression1:

Elif_suite

Else

Else_suite

2). No substitute for Switch/case

2. Extended If statement Example parsing:

For multiple branches, only one of the branches that satisfies the condition is executed

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Python three-day simple learning Day1