Python built-in function

Today we are going to learn some of the built-in functions in Python, because more, you can generalize these functions into 7 classes, specifically as

Scope-dependent

First, let's take a look at the function related to scope ====.> get local variables and global variables in the form of a dictionary

Globals ()------Get a dictionary of global variables

Locals ()------Gets a dictionary of local variables in the namespace in which this method is executed

Other

Input/output related

Usage of input

s = input ("")  # Enter content assigned to s variable print(s)  #  Enter what prints what. Data type is str

Input Inputs

Print output

f = open ('tmp_file','w')Print (123,456,sep=',', file = f,flush=true)

description of the file keyword

Import TimeImportSYS forIinchRange (0,101,2): Time.sleep (0.1) Char_num= I//2#How many # of printsPer_str ='%s%%:%s\n'% (I,'*'* Char_num)ifi = = 100Else '\r%s%%:%s'% (I,'*'*char_num)Print(per_str,end="', File=sys.stdout, flush=true) to implement the progress bar

Implementing the Print progress bar

Data type correlation

Type (' a ') returns the data type of the variable O

Memory-related

ID (o) o is a parameter that returns the memory address of a variable

Hash (o) O is a parameter that returns a hash value of a hash variable, and the non-hash variable will be hashed after the error.

T= (= = [n/a]print(hash (t))  # hashprint(hash (L))  # will error " Result: typeerror:unhashable type: ' list '" Hash instance

Hash Instance

Attention:

The hash function processes the current hash variable according to an internal algorithm, returning an int number.

* Each time the execution of the program, the same content of the variable hash value will not change during this time of execution.

File Operation related

Open () Opens a file that returns a file operator (file handle)

The mode of operation of the file has a total of 6 r,w,a,r+,w+,a+, each of which can be operated in binary form (rb,wb,ab,rb+,wb+,ab+)

You can specify the encoding with encoding.

Module Operation related

__import__ Importing a module

Help methods

In the console, perform help () to enter assist mode. You can enter variables or types of variables as you choose. Enter Q to exit

or directly execute Help (O), O is the parameter, view and variable o about the operation ...

Call the relevant

Callable (o), O is the parameter to see if this variable is callable.

If O is a function name, it returns true

def func ():passprint(callable (func))  # parameter is a function name, callable, returns True  Print(callable (123))   # parameter is a number, not callable, returns false

Callable Instances

View all built-in methods for the type of the parameter

Dir () View the properties in the global space by default, and also accept a parameter to view the methods or variables within this parameter

Print (dir (list))  # View the built-in methods for a list Print (dir (int))  # to view the built-in methods for integers

view built-in methods for a variable/data type

Execution of the STR type code

Built-in functions Eva, exec, Complie usage

eval () executes the string type code and returns the result

Print (Eval ('1+2+3+4'))

EXEC () executes code from the string type

Print (exec("1+2+3+4")) exec ("print (' Hello,world ')")

compile compiles the code of the string type. The code object can be evaluated by EXEC statement execution or eval ().

Parameter description:　　　

1. Parameter source: string or AST (Abstract Syntax Trees) object. That is, the code snippet that needs to be executed dynamically.　　

2. Parameter filename: The name of the code file, and some recognizable values are passed if the code is not read from the file. When the source parameter is passed in, the filename argument passes in a null character.　　

3. Parameter model: Specifies the type of compiled code that can be specified as ' exec ', ' eval ', ' single '. When the source contains a process statement, the model should be specified as ' exec '; When source contains only a simple evaluation expression, the model should be specified as ' eval '; When the source contains an interactive command statement, the model should be specified as ' single '.

>>>#The process statement uses the EXEC>>> Code1 ='For i in range (0,10): Print (i)'>>> compile1 = Compile (Code1,"','exec')>>>exec(Compile1)13579>>>#Simple evaluation expressions with Eval>>> Code2 ='1 + 2 + 3 + 4'>>> compile2 = Compile (Code2,"','Eval')>>> eval (compile2)

View Code

and number-related

Number--Data type Related: Bool,int,float,complex

Number--Binary conversion correlation: Bin,oct,hex

Numbers-mathematical operations: ABS,DIVMOD,MIN,MAX,SUM,ROUND,POW

Data structure related

Sequence--Lists and tuples Related: list and tuple

Sequence--string-Related: Str,format,bytes,bytesarry,memoryview,ord,chr,ascii,repr

Sequence: Reversed,slice

Data collection--dictionaries and collections: Dict,set,frozenset

Data collection: Len,sorted,enumerate,all,any,zip,filter,map

Add:

Use of map and filter

Map

The map function in Python is applied to each iteration of an item and returns a list of results. If other iterative parameters are passed in, the map function iterates through each parameter with the corresponding processing function. The map () function receives two parameters, one is a function, the other is a sequence, and map passes the incoming function to each element of the sequence sequentially, returning the result as a new list.

>>> L = [1,2,3,4defreturn x*>>> Map (pow2,l) [ 

Usage of Map

Filter

The filter () function receives a function f and a list, the function of which is to judge each element, return True or False,filter () automatically filters out the non-conforming elements according to the result of the decision, and returns a new list that is composed of qualifying elements.

Filter () to 1~100 that the square root is an integer number, i.e. the result should be:

[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]

Import Math def IS_SQR (x):     return math.sqrt (x)% 1 = = 0Print filter (IS_SQR, Range (1, 101)) The result is [1, 4, 9, 16, 25, 36 , 49, 64, 81, 100]

Usage of filter

With filter (), you can accomplish many useful functions, such as deleting None or an empty string:

 def   Is_not_empty (s):  return  s and  len (S.strip ()) >  0  >>>filter (is_not_empty, [ " Span style= "COLOR: #800000" >test   ", None,  ' ,  '  str   ' ,  " ,  '  ]) 

The result is
['test'str'END']

Built-in function sort

The list is sorted by the absolute value of each of these values

L1 = [1,3,5,-2,-4,-6= sorted (l1,key=ABS)print(L1)print(L2)

the list is sorted by absolute value

The list is sorted by the len of each element

L = [[1,2],[3,4,5,6], (7,),'123')print(sorted (L,key=len))

Exercises

1. Use map to process the list of strings and turn everyone in the list into SB, for example ALEX_SB

name=[' Alex ', ' Wupeiqi ', ' Yuanhao ', ' Nezha ']

2. Use the filter function to process the list of numbers and filter out all the even number in the list

num = [1,3,5,6,7,8]

3. Feel free to write a file with more than 20 lines

Run the program, read the contents into memory first, and store it in a list.

receive user Input page number, each page 5, output only when the content of the page

4. Below, the name of each dictionary corresponds to the stock name, shares corresponds to how many shares, price corresponds to the stock prices

Portfolio = [

{' name ': ' IBM ', ' shares ': +, ' price ': 91.1},

{' name ': ' AAPL ', ' shares ': +, ' price ': 543.22},

{' name ': ' FB ', ' shares ': $, ' Price ': 21.09},

{' name ': ' HPQ ', ' shares ': +, ' price ': 31.75},

{' name ': ' YHOO ', ' shares ': $, ' Price ': 16.35},

{' name ': ' ACME ', ' shares ': +, ' price ': 115.65}

]

4.1. Calculate the total price of each stock purchased

4.2. Filter out the stock with a unit price greater than 100

Python built-in function