python restarting a loop

Question

i have   for i in range 2 n       if something          do something     else         do something else        i   2   restart the loop   But that doesn t seem to work  Is there a way to restart that loop    Thanks

User · Answer

Changing the index variable i from within the loop is unlikely to do what you expect  You may need to use a while loop instead  and control the incrementing of the loop variable yourself  Each time around the for loop  i is reassigned with the next value from range    So something like   i   2 while i  lt  n      if something           do something     else          do something else         i   2   restart the loop         continue     i    1   In my example  the continue statement jumps back up to the top of the loop  skipping the i    1 statement for that iteration  Otherwise  i is incremented as you would expect  same as the for loop

User · Answer

You may want to consider using a different type of loop where that logic is applicable  because it is the most obvious answer   perhaps a   i 2 while i  lt  n      if something         do something        i    1     else          do something else          i   2  restart the loop

User · Answer

You may want to consider using a different type of loop where that logic is applicable  because it is the most obvious answer   perhaps a   i 2 while i  lt  n      if something         do something        i    1     else          do something else          i   2  restart the loop

User · Answer

Here is an example using a generator s send   method   def restartable seq       while True          for item in seq              restart   yield item             if restart                  break         else              raise StopIteration   Example Usage   x    1  2  3  4  5  total   0 r   restartable x  for item in r      if item    5 and total  lt  100          total    r send True       else          total    item

User · Answer

a     1    2    3   ls      count   False  while ls    a       print a count       if a count     a -1            count   count   1     else           count   False   Restart while loop

User · Answer

Changing the index variable i from within the loop is unlikely to do what you expect  You may need to use a while loop instead  and control the incrementing of the loop variable yourself  Each time around the for loop  i is reassigned with the next value from range    So something like   i   2 while i  lt  n      if something           do something     else          do something else         i   2   restart the loop         continue     i    1   In my example  the continue statement jumps back up to the top of the loop  skipping the i    1 statement for that iteration  Otherwise  i is incremented as you would expect  same as the for loop

User · Answer

Just wanted to post an alternative which might be more genearally usable  Most of the existing solutions use a loop index to avoid this  But you don t have to use an index - the key here is that unlike a for loop  where the loop variable is hidden  the loop variable is exposed    You can do very similar things with iterators generators   x    1 2 3 4 5 6  xi   iter x  ival   xi next   while not exit condition ival         Do some ival stuff     if ival    4          xi   iter x      ival   xi next     It s not as clean  but still retains the ability to write to the loop iterator itself    Usually  when you think you want to do this  your algorithm is wrong  and you should rewrite it more cleanly  Probably what you really want to do is use a generator coroutine instead  But it is at least possible

User · Answer

Just wanted to post an alternative which might be more genearally usable  Most of the existing solutions use a loop index to avoid this  But you don t have to use an index - the key here is that unlike a for loop  where the loop variable is hidden  the loop variable is exposed    You can do very similar things with iterators generators   x    1 2 3 4 5 6  xi   iter x  ival   xi next   while not exit condition ival         Do some ival stuff     if ival    4          xi   iter x      ival   xi next     It s not as clean  but still retains the ability to write to the loop iterator itself    Usually  when you think you want to do this  your algorithm is wrong  and you should rewrite it more cleanly  Probably what you really want to do is use a generator coroutine instead  But it is at least possible

User · Answer

Changing the index variable i from within the loop is unlikely to do what you expect  You may need to use a while loop instead  and control the incrementing of the loop variable yourself  Each time around the for loop  i is reassigned with the next value from range    So something like   i   2 while i  lt  n      if something           do something     else          do something else         i   2   restart the loop         continue     i    1   In my example  the continue statement jumps back up to the top of the loop  skipping the i    1 statement for that iteration  Otherwise  i is incremented as you would expect  same as the for loop

User · Answer

You may want to consider using a different type of loop where that logic is applicable  because it is the most obvious answer   perhaps a   i 2 while i  lt  n      if something         do something        i    1     else          do something else          i   2  restart the loop

User · Answer

a     1    2    3   ls      count   False  while ls    a       print a count       if a count     a -1            count   count   1     else           count   False   Restart while loop

User · Answer

You may want to consider using a different type of loop where that logic is applicable  because it is the most obvious answer   perhaps a   i 2 while i  lt  n      if something         do something        i    1     else          do something else          i   2  restart the loop

User · Answer

Here is an example using a generator s send   method   def restartable seq       while True          for item in seq              restart   yield item             if restart                  break         else              raise StopIteration   Example Usage   x    1  2  3  4  5  total   0 r   restartable x  for item in r      if item    5 and total  lt  100          total    r send True       else          total    item

User · Answer

Changing the index variable i from within the loop is unlikely to do what you expect  You may need to use a while loop instead  and control the incrementing of the loop variable yourself  Each time around the for loop  i is reassigned with the next value from range    So something like   i   2 while i  lt  n      if something           do something     else          do something else         i   2   restart the loop         continue     i    1   In my example  the continue statement jumps back up to the top of the loop  skipping the i    1 statement for that iteration  Otherwise  i is incremented as you would expect  same as the for loop

[python] python: restarting a loop

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