python basis - function scope

function

Function object

• Functions are first-class objects
• Function name can be referenced
• Function name can be used as parameters to use
• Function name can be used as the return value use
• Function name can be used as container type elements

Nested functions

• Nested call : calling a function inside the function

• Nested definitions : a function is defined inside the function

Namespaces

Storage variable name space, divided into built-in namespace , global namespace , local name space

• Built-in namespace : python, the name defined in advance, there is built-in namespace. For example: keywords, built-in method

• Global name space : stored in a file-level name is global name space

  IF / the while / for internally defined name in after the execution are stored in the global name space

  # if 的示例：
  var = 4
  if var > 5:
      var = "var 大于5"
  else:
      var = "var 小于等于5"
  print(var)        # 打印结果：var 小于等于5
  
  # while 的示例：
  num = 0
  while num <= 3:
      num += 1
  print(num)        # 打印结果：4
  
  # for 的示例
  for i in range(2):
      pass
  print(i)      # 打印结果：1

• The local name space : internal function definition all the names are stored in the current built-in namespace function

If you want to access a variable value, you must first access the corresponding name space, access to the relationship between the name and the names and values ​​of the memory address of the variable.

The life cycle

• Built-in namespace : Python interpreter take effect when you start, fail closed
• Global name space : the current python file execution into force, after the failure of execution
• The local name space : the function becomes effective when called, the function body codes lapse at the end of the

Find the order

• The local name : Local → global → built-in functions

• Global Name : Global → built

  Built-in error will not be found again

• Internal function name used in the definition phase has been specified dead, with nothing to call the location

Scope

• The global scope : global can call names exist in the global scope. Built-in namespace and global name space belong here

• The local scope : Local can call the name exists in the local scope. The local name space belong here

• , Ltd. Free Join : The local namespace variable declared as global variables

  Note: , Ltd. Free Join declare inside a function , if statement outside the function, the function is still not operating

  # 这种情况不能修改x1的值
  x1 = 1
  def func1():
      x1 = 2
  func1()
  print(x1)  # 打印结果：1
  
  # 使用global 后，可以修改x2的值
  x2 = 1
  def func2():
      global x2 # 先声明成全局变量
      x2 = 2
  func2()
  print(x2) # 打印结果：2
  
  # global 若在函数外声明，无法操作变量
  global x3
  x3 = 1
  def func2():
      x3 = 2
  func3()
  print(x3) # 打印结果：1

• nonlocal : In the local namespace declarations local variables .

  After nonlocal variable declaration will start from the outer layers of a function of the current function to find the variable. If all the way to the outermost function can not be found, an exception is thrown.

  def f3():
      x = 4
      def f1():
          y = 2
          def f2():
              nonlocal x
              x = 3
          f2()  # 调用f2(),修改f1作用域中名字x的值
          print(x)  # 在f1作用域查看x。打印结果：3
      f1()
      print(x)  # 打印结果：3
  f3()

  def f3():
      x = 4
      def f1():
          x = 2
          def f2():
              nonlocal x
              x = 3
          f2()  # 调用f2(),修改f1作用域中名字x的值
          print(x)  # 在f1作用域查看x。打印结果：3
      f1()
      print(x)  # 打印结果：4
  f3()