Getting started with "Safe cow learning Notes" python

First Lecture python Getting Started with

The 1.python version can be divided into 2.x and 3.x

python3.x disadvantages are not backwards compatible

2. Advantages of using python:

Simple syntax, high readability, high development efficiency, no need to compile, good portability, etc.

3. What you can do with python

system programming, user graphics interface,Internet scripting, database programming, etc.

4.python Parser

The Shell is our common parser, one-by-one execution of statements

5. the use of single and double quotes is basically the same, with \ n or "(" "") to Wrap, with # to annotate

>>> a= "Hello \ n World"

>>> Print (a)

Hello

World

>>> a= "' Hello

World ""

>>> Print (a)

Hello

World

Second lecture python types and operations of - Mathematics (I.)

1. Number Types

python3.x version integers have only one type.

Binary :0b or 0B bin (x)

octal:0o or 0O Oct (x)

16 binary:0x or 0X hex (x)

Int (str,base) base is 2,8,16 number

Repr (x): display mode when interactive mode

plural:complex (3,5) or 3+5j

Score: Fraction (3,5) or 3/5

2. operators:

Arithmetic Operators

Comparison operators

Assignment operators

Bitwise operators

logical operators

member operator : In,not in

identity operator:is, was not

Third Speaking python types and operations of - Mathematics (ii)

1. Operator Precedence

* * 2**100 is a 2 - Time Square

+,- plus and minus are unary operations

Multiplication

Add and Subtract

Wait a minute

2. Import Functions

Fraction () function

From fractions import fraction

Random () function

Import Random

3. Basic Mathematical Functions

Pow: power function

Abs: Absolute Value

Fabs: Absolute Value

Round: Rounding

Ceil,floor: rounding (math)

Int,bin,oct,hex,float: format Conversion

Random: Stochastic function

CMP: comparison function

LOG: natural logarithm

Max,min: Select Maximum, minimum value

MODF: Dividing floating-point numbers into small-tree and integer-parts

Sqrt: square root

Fourth Lecture python types and operations of - Introduction to Dynamic Types

1. in python , the variable has no type

A variable is a pointer to an object

object is a piece of memory allocated

A variable is a reference to an object

2. Collection of Objects

3. Shared References

Two variables can share an object

Shared references for lists

>>> list1=[1,2,3]

>>> List2=list1

>>> list1[0]=24

>>> List2[0]

24

>>> list1=[1,2,3]

>>> list2=list1[:]

>>> list1[0]=24

>>> List2[0]

1

4. >>> a=3.14

>>> b=3.14

>>> a==b

True

>>> A is B #a and b do not share an object

False

5. you need to know how many times an object is referenced and can be viewed using the following function

>>> Sys.getrefcount

>>> Sys.getrefcount (1)

Fifth Lecture python types and operations of - string (i)

the string in 1.python is divided into immutable sequences.

2. string constant - escape

escape character:\

Raw string:r "my\new" # \ does not escape

\ \: Two backslash essentially represents a backslash, the first backslash means escape

\ ': Single quote

\ ": double quotation marks

\a: Bell

\b: backward (one person)

\f: page Change

Wait a minute

3. in python3.x , the default is Unicode

>>> Len (" Chinese ")

2

4. string Manipulation

convert strings into corresponding code with Ord and CHR

>>> Ord (' a ')

97

>>> chr (97)

A

5. >>> a= "This is test"

>>> A[0:4]

' This '

>>> A[4]

‘ ‘

6. display the previous line : Alt+p (previous)

Show Next line:Alt+n (Next)

Sixth lecture python types and operations of - String Method

1. string Method - method call

Case-sensitive

>>> "Hello". Capitalize ()

' Hello '

>>> "HelloWorld". Title ()

' Hello World '

>>>

Typesetting related

Find related

Format judgment

Character separation

2. string Formatting expressions - formatting code

Seventh Lecture python types and operations of - string Formatting Expressions

usage of format in 1.python

>>> ' What does youlike,{0},{1},{2} '. Format (' spam ', ' egg ', ' ham ')

' What does you Like,spam,egg,ham '

2. >>> Import sys

>>> Sys.platform

Eighth lecture python discussion - string - a scene (i)

1. separating strings with multiple qualifiers

Import RE # introducing regular Expressions

>>> line= ' Who,what.when;where:whyhow '

>>> Import re

>>> Re.split (R ' [,.;: \ S]\s* ', line) #\s as a space

["Who", "what", ' when ', ' where ', ' why ', ' how ')

2. string start or end match

>>> url= ' Https://mylog.log '

>>> txt= ' Mytxt.txt '

>>>url.startswith (' https://', '/http ', ' ftp://')

True

>>> txt.endswith (' log ', ' txt ')

True

3. Match a string with a shell wildcard character

4. string matching and search

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Getting started with "Safe cow learning Notes" python