The use of--eval (), the path of the Python precipitation

One, the Eval function

The function of the Python eval () function: evaluates the string str as a valid expression and returns the result of the calculation.

Syntax: eval (source[, globals[, locals]), value

Parameters:

Source: The code object returned by a Python expression or function compile ()

Globals: Optional. It must be dictionary.

Locals: Optional. Arbitrary map Object

If the globals parameter is provided, it must be a dictionary type, or it can be an arbitrary map object if the locals parameter is provided.

The global namespace of Python is stored in a Dict object called Globals (), and the local namespace is stored in a Dict object called locals (). We can use print (locals ()) to view all variable names and variable values in the function body.

1x = 12y = 13num = eval ("X+y")4 Print('Num', num)5 6 defg ():7x = 28y = 29NUM1 = eval ("X+y")Ten     Print('NUM1', NUM1) OneNum2 =eval ("X+y", Globals ()) A     Print('num2', num2) -num3 = eval ("X+y", Globals (), locals ()) -     Print('num3', num3) the  -G ()

1 num 22 num1 43 num2 24 num3 4

Parsing: num2 Because there is globals so is a global variable, after the result is 4;num3 both globals and locals, only in this case, priority to use the value of locals, so the result is 2

Second, the Eval can convert list, tuple, dict to STR, return to also set up;

 1  #  ### ###########  2  #   string into list  3  s = "  [[1,2,],[3,4,],[5,6,],[8,9]]   " 4  li = eval (s)  5  print   (li  6  print   (type (s))  7  print  (Type (LI)) 

 1  [[1, 2], [3, 4], [5, 6], [8, 9]]  2  <class    str   " > 3  <class   " list  ; 

 1  #  ### ####################  2  #   string into dictionary  3  s =  {1: ' A ', 2: ' B '}   " 4  dic = eval (s)  5  print   (DIC)  6  print   (type (s))  7  print  (Type (DIC)) 

 1  {1:  " a  , 2: "  b   " }  2  <class   " str   " >3  < class   " dict  ; 

 1  #  ### #######################  2  #   string to tuple  3  s =    ([Up,], (3,4,), [5,6,], (8,9))   " Span style= "COLOR: #008080" >4  tu = eval (s)  5  print   (TU)  6  print   ( Type (s))  7  print  (Type (TU)) 

1 ([1, 2], (3, 4), [5, 6], (8, 9))2 <class'str'> 3 <class'tuple'>

The use of--eval (), the path of the Python precipitation