How does the code work [I for i in Range (51) if I % 2 == 0]?

or in a more general form:

  [expr (variable)  for  variable  in  iterable  if  Condition (Variable)]     
 here: 
  
  
  
  iterable  & mdash; A certain object from which you can receive values ​​one by one (until it ends). List, motorcade or, for example, dictionary keys. From here the values ​​are taken by the variable  variable . Alteate operations are called "" iterations "", and the above object & mdash; . 
  
 the expression  range (51)  retus a list of natural numbers from 0 to 50 inclusive. We are sorting out. 
  
  
  variable  (arbitrary name) & mdash; Just a variable, alteately accepting all values ​​from  iterable . It works in the same way as a meter in the cycle. 
  
  
  Expr (Variable)  & mdash; Any function that retus value. She can take an argument of  variable , maybe anything else, can not accept anything at all. It is clear that  i  retus simply the value of  i  unchanged. The values ​​retued by this function become elements of the generated list. Other examples: 
  
  
  [I ** 2 for i in Range (51)]  & ndash; Squares of numbers 
  
  [0 for i in Range (51)]  & ndash; & nbsp; just fill out zero 
  
  
  
  
  control (Variable)  & mdash; An optional condition. If it is present, then the resulting list will include only those values ​​for which  control (Variable) == True . You can write one  if , but inside it can be an arbitrarily complicated expression, i.e.  if a (i) and b (i) or c (i) ...  
  
 In this case, those numbers that are multiplied by two (i.e., even).