2. Python program Control structure (0530)

Condition test:

1.If condition test expression

String: A dictionary-by-character comparison in alphabetical order (by alphabet or ASCII code)

2. True and False in Python:

• Any non-0 numeric and non-empty objects are true
• Number 0, empty object, and special object none are False
• Comparisons and equality tests are applied recursively to the data structure
• The return value is TRUE or False

3. Combination condition test:

• X and Y: with operations
• X or Y: or operation
• Not x: Non-operational

The syntax structure of the IF test

A = X if y else Z//if y condition satisfies, a=x, otherwise a=z, ternary expression

If Y:

A=x

Else

A=z

While and for loops

.......

While syntax format:

While Bool_expression:

While_suite

Else

Else_suite

Break: Jump out of the inner loop

Continue: Jumps to the beginning of the closest layer loop where it is located

Pass: Bit statement

Else code library: The loop terminates normally, and if the loop termination is caused by a break, else does not execute

Exercise 1: Display all the elements in the specified list individually;

Exercise 2: Ask for all even numbers within 100 and;

Contact 3: Displays all keys of the specified dictionary one by one, and displays the total number of keys after the end;

While true: Dead loop

Review:

1. Dynamic language

Sys.getrefcount ()

Increase the object's reference count scenario

When the object is created:

When adding objects to a container: Lis

T.append ()

When an object is passed as a parameter to a non-function

Create an additional variable name for an object

Reduce reference count

A variable name referencing this object is displayed for destruction: Del X

A variable name that references this object is re-assigned

When removing objects from a container, similar to List.pop ()

The container itself is destroyed

2.if

If boolean_exprssion:

....

Elif boolean_exprssion:

....

Else

....

3.while

While Boolean_exprssion:

While_suite

If Boolean_esprssion2:contine

If Boolean_esprssion3:break

Else

Else_suite

4.for

For Exprssion in object:

While_suite

If Boolean_esprssion2:contine

If Boolean_esprssion3:break

Else

Else_suite

Raw_input: Enter a content

Iteration: Doing one thing over and over again

List resolution:

Generate a new list based on an existing list

File object:

Text is a sequence of bytes

Var_name = open (File_name[mode,[bufsize]])

Mode

R

W

A

r+

w+

A +

b means that the file is opened in binary mode

Rb

Wb

Ab

rb+

wb+

ab+

Cache:

0 means no cache is used

A negative number means using the system default cache

1 means using the cache

integers represent buffers that use size

File.seek (Offset[whence])

Whence: Starting point

0: From the file header

1: From the current position

2: From the end of the file

Offset: Offsets

File system module: OS

Directory:

ChDir (): Switch working directory

Chroot (): Sets the root directory of the current process

Listdir (): Lists all filenames under the specified directory

mkdir (): Create the specified directory

Makedirs (): How long to create a directory

GETCWD (): Get working directory

RmDir (): Delete directory

Removedirs (): Delete Multilevel directory

File:

Mkfifo (): Create pipeline

Mknod (): Create a Device file

Remove (): Delete file

Unlink (): Delete linked file

Rename (): renaming

Stat (): Put back the status information of the file

Symlink (): Create a linked file

Utime (): Update timestamp

Tmpfile (): Create and open (W+B) a new temporary file

Walk (): Creating a directory tree

Access rights-related

Access (): Verify the permission mode for a user or group of users

chmod (): Modify Permissions

Chown (): Modify the owner and the genus Group

Umask (): Set default permission Mode

File Descriptor:

Open (): open () of the underlying operating system

Read ():

Write ():

Device files:

Makedev ():

Major (): Get the main device number

Minor (): Gets the secondary device number

Path Management:

Import Os.path

basename (): Path base Name

DirName (): Path directory Name

Join (): Consolidated file name

Split (): Returns DirName (), basename () tuple

Splitext (): Return (filename,extension) tuple

Information:

Getatime ()

Getctime ()

Getmtime ()

GetSize (): Returns the size of the file

Inquire

Exists (): Determines whether the specified file exists

Isabs (): Determines whether the specified path is an absolute path

Isdir (): Whether it is a directory

Isfile (): Whether it is a file

Islink (): Whether it is a symbolic link

Ismount (): Whether it is a mount point

Samefile (): Two paths pointing to the same file

Exercise: Determine if a file exists, open it

Allow users to repeatedly enter multiple rows of data through the keyboard

Append save to this file

#!/usr/bin/python

Import OS

Import Os.path

Filename=raw_input (' plz a file name: ')

If Os.path.isfile (filename):

Openname= open (filename, ' A + ')

While True:

Newline=raw_input (' plz a line: ')

if newline = = ' Q ' or newline = = ' Quit ':

Break

Else

Openname.write (newline+ ' \ n ')

Openname.close ()

Object Persistent Storage

Pickle

Marshal

DBM Interface

Shaelve Module

2. Python program Control structure (0530)