Python collections, functions

 * Collection:

set: holds a series of elements, but the set element is not duplicated and is unordered

How to create:set () and pass in a list,thelist element will be set the element.

S=set ([' A ', ' B ', ' C ']) print (s)//set ([' A ', ' C ', ' B ']) print (Len (s))//3

How to access: Use inch operator to determine if there is

= ([,,,]) ()//true

set Features of:

1. The internal structure and the dictionary are very similar, the only difference is not to store the value

= ([,,,,,,]) X1=x2=x1: () (x2): ()//ok

Traverse set:

traversing a set through a for loop

= ([(,), (,), (,)]) x:x[],,x[]

Lisa:85adma:95bart:50

Update Set

Two things:1 Add a new element to the set

2 Remove an existing element from the set

        add element sets.add ( new element

S=set ([+]) add

eg

s=Set([1,2,3])
S.Add(4)
Print (s)//set ([1, 2, 3, 4])

Remove (): remove elements from set

sets.remove ( deleted element)

Add () can be added directly, with remove () before you need to determine

* function

What is a function: a chunk of reusable code that is a named block of code that accepts input, provides output, and can be stored in a file for later use.

calling functions

functions are divided into two main categories: custom functions, built-in functions

A. Pow (x , y) calculates the y of X**y x Sub-party

to invoke a function by ()

Print (POW (2,5))//32

The function has no input (no arguments) and must be added after the function ()

If you do not add (), it points to a function.

B. cmp (x, y), ifX<y,return-1, ifx==y, return0, ifX>yreturn 1 [2,34,1,5,98]

C. sum (x, y,...) Print sum ([1,6])

d. append () to add a new object at the end of the list

list.append ( obj)-obj objects added to the end

E. functions that do not return a value Print

=[]x=x<=:. Append (X*x) x=x+ (())//42925 If the function does not return a value, it returns none

Assigning a value to a function in Python will result in the inability to access the function you originally pointed to, and you need to restart Python

Custom functions: Use the DEF statement to write down the function name, parentheses, parameters in parentheses, and: And then write in the indent block
function body, the return value of the function is returned with a return statement.

Function name: can only contain letters, numbers, and underscores, and cannot begin with a number, indicating the simple name of its purpose.

def names (x):
function body
Return

Names (parametric)

NOTE: When the statement inside the function body executes, once it executes to the return statement, the function is completed and the result
Return. Therefore, it is possible to achieve very complex logic through conditional judgment and loop inside the function.
If there is no return statement, the result will be returned when the function is finished, and the result will be none
Return also returns none of Return
Return can be placed anywhere in the function, usually at the end.

Scope of the variable:
An important problem with a function is the scope, the scope of the variable, and the location of the program where it can be accessed
or visible.
Divided into two types: local scope, global scope
Local variables, global variables

F/elif/else try/execpt/final for/while do not sink into variable scope changes, they are in the code block of the
variables, which can also be accessed externally.

Search paths for variables: Local variables >> global variables

To modify a local variable to be the global variable: global

Lifetime of local variables: Local variables can only be used in functions, and local variables are automatically deleted when the function ends

Global Volume: Variables declared outside the function, any code in the program and any function can be read, however, in the function
You need to be particularly careful when assigning values to global variables in duplicate

Key words:
Words with special meanings, also known as reserved words, are pre-defined and special identifiers in the computer.

The keywords in Python include the following: The keyword cannot be used as a function name

And Del form while as Elif global with assert else if pass break import
Print class in Exec raise continue finally are return for lambda try

Parameters: Formal parameter types that can be used when calling a function

1. Required Parameters
2. Keyword parameters
3. Default parameters
4. Indefinite length parameter

1. Required parameters: Pass in the function in the correct order, the number of calls must be the same as when declaring

Exercise: Define a function that displays name and age

2. Keyword parameters:

Close to the function call, the function call uses the keyword argument to determine the passed-in parameter value.
The order of the arguments is not consistent with the declaration when using the keyword argument to allow the function call, and the Python interpreter can use the parameter name
Match the parameter value.

3. Default parameters:

When a function is called, the value of the default parameter is considered to be the default value if it is not passed in

4. Indefinite length parameter

You may need to deal with a function that has more arguments than was originally declared, and these parameters are called indeterminate length parameters.
* All unnamed variable parameters are stored.

def function name (*info)

Anonymous functions:

Using lambda to create anonymous functions
The body of a lambda is an expression, not a block of code
Note: Anonymous functions can contain only one statement

Grammar:

var = lambda arg1,arg2 ...: (expression)

Python module

Save a Python code file, the module can define functions, classes and variables, the module can also contain executable code

Import statement: Introducing modules

Syntax: Import module (block name) ...

Note: A module will only be imported once, no matter how many times you import it. This prevents the import module from executing again and again

This article from "Liu Xiao Rabbit" blog, declined reprint!

Python collections, functions