For and While

If we want  to do some operation or set of operations various  times, we can handle the process  in several  different types.  The most straightforward types are for and while statements (often called for and while loops).

A for loop has the following form:

for in :

...

The interpreter starts  by calculating listExpr.  If it does not yield a list, tuple,  or string7,  an error occurs.  If it does yield a list-like structure or list, then  the block of instructions will, under normal conditions, be executed one time for every  value  in that  list.  At the end,  the variable will remain bound to the last element of the list (and  if it had  a useful  value  before the for was calculated, that number  will have been permanently overwritten).

Here is a basic for loop:

result = 0

for x in [1, 3, 4]:

result = result + x * x

At the end of this execution, result will give the value  26, and x will have the value  4.

One situation in which  the body  is not executed once for each value  in the list is when  a return statement is encountered. No situations whether value is nested in a structure or not, if it is calculated it immediately gives a problem a value to be returned from a function call. So, for example, we may  write a function that tests to see if an item is a member of a list, and gives True if it is and 0 if it is not, as given:

def member(x, items):

for i in items:

if x == i:

return True return False

The procedure loops  through all of the components in items, and  relates them  to x. As soon as it ?nds  an item i that  is same  to x, it can quit  and  return the value  True from the method. If it has all the way through the loop without giving any value, then we know  that x is not in the structure, and we may give False