python05-namespaces/scopes/recursion

First, namespace and scope

1. Namespaces

Where the name is stored, there are three types of namespaces (previously left x=1,1 stored in memory, where does the name x reside?). Namespaces are where the name X and 1 bindings are stored)

2. Loading order of namespaces

Python test.py
#1, the Python interpreter starts first, so it first loads: built-in namespaces
#2, execute the test.py file, and then load the global namespace on file basis
#3, if a function is called during the execution of a file, the local namespace is generated temporarily

3. Search Order of Names

Local namespace---> Global namespaces---> built-in namespaces

#需要注意的是: In the global cannot view local, in the local can view the global, the following example
# max=1
# def F1 ():
# max=2
# def F2 ():
# max=3
# Print (max)
# F2 ()
# f1 () #打印3
# print (max) #打印1

4. Scope
#作用域即范围
-Global scope (the built-in namespace and the global namespace belong to this scope): Global survival, globally valid
-Local scope (local namespace belongs to this range): temporary survival, partially valid

# # #全局变量

A variable defined at the beginning of a program, scoped to the entire program

# NAME = "Product Manager"
# def Yangjian ():
# print (' I'm going to do ', NAME)

# print (' I'm going to do ', NAME)

# Yangjian ()

# # #局部变量

A variable defined in a subroutine, scoped to a subroutine that defines the variable

# def Qupengfei ():
# NAME = "Base"
# print (' I'm going to do ', NAME)

# Qupengfei ()

Second, global and nonlocal

1.global keywords

The ability to declare a variable inside a subroutine as a global variable, as in the following example:

# If there is no global keyword inside the function
#-have declared local variables
# NAME = ["Product Manager", "Riopo Wet"]
# def Qupengfei ():
# NAME = "Self" #只找自己的局部变量
# print (' I'm going to do ', NAME)
# Qupengfei () #打印我要搞自己
#-No declaration of local variables
# NAME = ["Product Manager", "Riopo Wet"]
# def Qupengfei ():
# name.append (' Xxoo ') #自己没有局部变量就找全局变量
# print (' I'm going to do ', NAME)
# Qupengfei () #打印我要搞 ["Product manager", "Riopo Wet"]

# If the contents of the function have the global keyword
#-have declared local variables
# NAME = ["Product Manager", "Riopo Wet"]
# def Qupengfei ():
# Global NAME
# NAME = "Self" # same as "local variable with no declaration of the same name"
# print (' I'm going to do ', NAME)
# Qupengfei () #打印我要搞自己
-# Error Example
# NAME = ["Product Manager", "Riopo Wet"]
# def Qupengfei ():
# NAME = "Self"
# Global NAME
# print (' I'm going to do ', NAME) #报错, global must be close to the function def
# Qupengfei ()
#-Local variables with no declaration of the same name
# NAME = ["Product Manager", "Riopo Wet"]
# def Qupengfei ():
# Global NAME
# NAME = ["Mao"] #OK的
# name.append (' Xxoo ')
# print (' I'm going to do ', NAME)
# Qupengfei () #打印我要搞 ["Mao"], the list of elements is ["Mao", ' Xxoo ')

# Summary
# If there is no global keyword inside the function, first read the local variable, no local variable reads the global variable, cannot be globally re-assigned (name= "FFF"), but for the mutable type (list, dictionary, etc.), you can manipulate the inner element.
# If there is a global keyword in the function, the variable is essentially the global variable and can read the re-assigned value name= "FFF"
# Spec: global variable name uppercase, local variable lowercase

#在定义局部变量的子程序内, local variables work, and in other places, global variables work

2.nonlocal keywords

Specify the upper-level variable, and if not, continue up until you find it, as in the following example:

Name = "Just Niang"
Def Weihou ():
Name = "Chen Zhuo"
Def Weiweihou ():
Global name # refers to Globals
Name = "Cool" # So the change is a global variable

Weiweihou ()
Print (name)

Print (name)
Weihou ()
Print (name) # just Niang---> Chen Zhuo---> Cool

Name = "Just Niang"
Def Weihou ():
Name = "Chen Zhuo"
Def Weiweihou ():
nonlocal name # nonlocal, specify the upper-level variable, and if not, continue up until you find it
Name = "Cool"

Weiweihou ()
Print (name)

Print (name)
Weihou ()
Print (name) # just Niang---> cool----> Just Niang

Three, nested functions

1. Definition

A function body contains one or more function bodies

2. Execution procedure of nested functions

#1. Name= ' Yyq '
#2. Def huangwei ():
# 4.1.name = "Zyh"
# 4.2.print (name)
# 4.3.def Liuyang ():
# 4.4.1.name = "YJJ"
# 4.4.2.print (name)
# 4.4.3.def Nulige ():
# 4.4.5.1.name = ' ZJQ '
# 4.4.5.2.print (name)
# 4.4.4.print (name)
# 4.4.5.nulige ()
# 4.4.liuyang ()
# 4.5.print (name)

#3. Print (name)
#4. Huangwei ()
#5. Print (name)

Iv. function as Variable

Let's look at a few examples:

# def foo ():
# print (' from foo ')
# Bar ()
# foo () #报错, bar () not defined

# def bar ():
# print (' from Bar ')
# def foo ():
# print (' from foo ')
# Bar ()
# foo () #执行通过

# def foo ():
# print (' from foo ')
# Bar ()
# def bar ():
# print (' from Bar ')
# foo () #执行通过

# def foo ():
# print (' from foo ')
# Bar ()

# foo () # Error, could not find bar ()

# def bar ():
# print (' from Bar ')

Summary: In the computer, the function is treated as a long string of strings into memory, to get a memory address, and the function name is equivalent to a variable name (house number), the function name parentheses is the memory address of the call function.

V. Recursion

1. Definition

A function call itself is called recursion, the maximum number of recursion is 999 times, the example is as follows:

# def Calc (n):
# print (n)
# if int (N/2) = = 0:
# return N
# res=calc (int (N/2))
# return Res
#
# Res=calc (#每一层都print一个数字)
# Print (res) #返回最后的结果1

2. Characteristics of recursion

There must be a definite end condition (so a return is required); each step into a deeper level of recursion, the problem size is less than the previous layer; Recursive efficiency is not high (recursive write bad, easy memory overflow)

One more example of asking the way:

# import Time
# person_list=[' Yyq ', ' zyh ', ' ljy ', ' ZSC ']
# def Ask_way (person_list):
# print ('-' *60)
# If Len (person_list) = = 0:
# return ' No one Knows '
# person=person_list.pop (0) #使得列表中的人不断减少 (problem size reduction), after Len (person_list) is to prevent the first pass in the empty list causes an error
# if person = = ' Linhaifeng ':
# return '%s ' said: I know that the South base is on the High Pond Road '%person
#
# print (' Hi-man [%s], dare to ask where the road is '% person ')
# print ('%s ' replied: I don't know, but read your eyes to the pig, you wait, I help you ask%s ... '% (person, person_list))
# Time.sleep (10)
# Res=ask_way (person_list) #第一个人不知道, so he went to ask another person, and so on and on, knowing the result, and then returning to the layer
#
# print ('%s ' results were:%res '% (person,res))
# return Res
#
# Res=ask_way (person_list) #把函数的返回值暂时保存, for the next sentence to print out
# Print (RES)

python05-namespaces/scopes/recursion