Re: Noob: Loops and the 'else' construct
* Dustan (Fri, 19 Oct 2007 11:39:04 -) On Oct 19, 3:12 am, Thorsten Kampe [EMAIL PROTECTED] wrote: So a for/else loop is exactly the same thing as a for loop with the else clause outside the loop (except for break)? Am I missing something here? It sounds to me like you just described two identical constructs. # for i in range(10): print i else: print 'the end!' # is the same else # for i in range(10): print i print 'the end!' # -- http://mail.python.org/mailman/listinfo/python-list
Re: Noob: Loops and the 'else' construct
MRAB schrieb: On Oct 19, 4:11 am, Gabriel Genellina [EMAIL PROTECTED] wrote: En Thu, 18 Oct 2007 23:44:27 -0300, Ixiaus [EMAIL PROTECTED] escribió: I have just come across a site that discusses Python's 'for' and 'while' loops as having an (optional) 'else' structure. At first glance I interpreted it as being a bit like the 'default' structure in PHP's switch block... But the switch block isn't a loop, so, I am now confused as to the reason for using 'else' with the for and while loops... A few quick tests basically show that statements in the else structure are executed at the fulfillment of the loop's expression (ie, no break). A `while` loop tests a condition: if it evaluates to true, keep cycling; if it is false, stop. The `else` clause is executed when the condition is false, as in any `if` statement. If you exit the loop by using `break`, the `else` part is not executed (because you didn't get out of the loop by determining the condition falseness) You can think of a `for` loop as meaning `while there are remaining elements to be iterated, keep cycling` and the `else` clause applies when there are no more elements. A `break` statement does not trigger the else clause because the iteration was not exhausted. Once you get the idea, it's very simple. It's useful when you want to search for an item and to do something if you don't find it, eg: for i in items: if is_wanted(i): print Found it break else: print Didn't find ir Wrong. It's not: for i in []: print i else: print I'm reached, too prints out I'm reached, too The else will ONLY not get executed when the loop is left prematurely through a break: for i in [1]: print i break else: print I'm reached, too won't print the I'm ... Diez -- http://mail.python.org/mailman/listinfo/python-list
Re: Noob: Loops and the 'else' construct
On Oct 19, 4:11 am, Gabriel Genellina [EMAIL PROTECTED] wrote: En Thu, 18 Oct 2007 23:44:27 -0300, Ixiaus [EMAIL PROTECTED] escribió: I have just come across a site that discusses Python's 'for' and 'while' loops as having an (optional) 'else' structure. At first glance I interpreted it as being a bit like the 'default' structure in PHP's switch block... But the switch block isn't a loop, so, I am now confused as to the reason for using 'else' with the for and while loops... A few quick tests basically show that statements in the else structure are executed at the fulfillment of the loop's expression (ie, no break). A `while` loop tests a condition: if it evaluates to true, keep cycling; if it is false, stop. The `else` clause is executed when the condition is false, as in any `if` statement. If you exit the loop by using `break`, the `else` part is not executed (because you didn't get out of the loop by determining the condition falseness) You can think of a `for` loop as meaning `while there are remaining elements to be iterated, keep cycling` and the `else` clause applies when there are no more elements. A `break` statement does not trigger the else clause because the iteration was not exhausted. Once you get the idea, it's very simple. It's useful when you want to search for an item and to do something if you don't find it, eg: for i in items: if is_wanted(i): print Found it break else: print Didn't find ir -- http://mail.python.org/mailman/listinfo/python-list
Re: Noob: Loops and the 'else' construct
On Oct 19, 3:12 am, Thorsten Kampe [EMAIL PROTECTED] wrote: So a for/else loop is exactly the same thing as a for loop with the else clause outside the loop (except for break)? Am I missing something here? It sounds to me like you just described two identical constructs. Guess that's why I never used that... Thorsten -- http://mail.python.org/mailman/listinfo/python-list
Re: Noob: Loops and the 'else' construct
* Gabriel Genellina (Fri, 19 Oct 2007 00:11:18 -0300) En Thu, 18 Oct 2007 23:44:27 -0300, Ixiaus [EMAIL PROTECTED] escribió: I have just come across a site that discusses Python's 'for' and 'while' loops as having an (optional) 'else' structure. At first glance I interpreted it as being a bit like the 'default' structure in PHP's switch block... But the switch block isn't a loop, so, I am now confused as to the reason for using 'else' with the for and while loops... A few quick tests basically show that statements in the else structure are executed at the fulfillment of the loop's expression (ie, no break). A `while` loop tests a condition: if it evaluates to true, keep cycling; if it is false, stop. The `else` clause is executed when the condition is false, as in any `if` statement. If you exit the loop by using `break`, the `else` part is not executed (because you didn't get out of the loop by determining the condition falseness) So a for/else loop is exactly the same thing as a for loop with the else clause outside the loop (except for break)? Guess that's why I never used that... Thorsten -- http://mail.python.org/mailman/listinfo/python-list
Re: Noob: Loops and the 'else' construct
On 19 Okt, 13:39, Dustan [EMAIL PROTECTED] wrote: On Oct 19, 3:12 am, Thorsten Kampe [EMAIL PROTECTED] wrote: So a for/else loop is exactly the same thing as a for loop with the else clause outside the loop (except for break)? Am I missing something here? It sounds to me like you just described two identical constructs. Think of the loop-plus-else construct as behaving like this: while 1: # Get next element (in a for loop) if loop_condition: # eg. whether we have an element # Loop body statement else: # Loop else statement break Taking the example... for i in range(10): print i else: print 'the end!' This is equivalent to... while 1: # Get next element (from the range iterator) if next element: # yes, it's more complicated than this print i else: print 'the end!' break Now consider what happens if you put a break statement inside the for loop. Paul -- http://mail.python.org/mailman/listinfo/python-list
Re: Noob: Loops and the 'else' construct
En Thu, 18 Oct 2007 23:44:27 -0300, Ixiaus [EMAIL PROTECTED] escribió: I have just come across a site that discusses Python's 'for' and 'while' loops as having an (optional) 'else' structure. At first glance I interpreted it as being a bit like the 'default' structure in PHP's switch block... But the switch block isn't a loop, so, I am now confused as to the reason for using 'else' with the for and while loops... A few quick tests basically show that statements in the else structure are executed at the fulfillment of the loop's expression (ie, no break). A `while` loop tests a condition: if it evaluates to true, keep cycling; if it is false, stop. The `else` clause is executed when the condition is false, as in any `if` statement. If you exit the loop by using `break`, the `else` part is not executed (because you didn't get out of the loop by determining the condition falseness) You can think of a `for` loop as meaning `while there are remaining elements to be iterated, keep cycling` and the `else` clause applies when there are no more elements. A `break` statement does not trigger the else clause because the iteration was not exhausted. Once you get the idea, it's very simple. -- Gabriel Genellina -- http://mail.python.org/mailman/listinfo/python-list
Noob: Loops and the 'else' construct
I have just come across a site that discusses Python's 'for' and 'while' loops as having an (optional) 'else' structure. At first glance I interpreted it as being a bit like the 'default' structure in PHP's switch block... But the switch block isn't a loop, so, I am now confused as to the reason for using 'else' with the for and while loops... A few quick tests basically show that statements in the else structure are executed at the fulfillment of the loop's expression (ie, no break). Example: for i in range(10): print i else: print 'the end!' 0 1 2 3 4 5 6 7 8 9 10 the end! -- http://mail.python.org/mailman/listinfo/python-list
Noob: Loops and the 'else' construct
I have just come across a site that discusses Python's 'for' and 'while' loops as having an (optional) 'else' structure. At first glance I interpreted it as being a bit like the 'default' structure in PHP's switch block... But the switch block isn't a loop, so, I am now confused as to the reason for using 'else' with the for and while loops... A few quick tests basically show that statements in the else structure are executed at the fulfillment of the loop's expression (ie, no break). Example: for i in range(10): print i else: print 'the end!' 0 1 2 3 4 5 6 7 8 9 10 the end! -- http://mail.python.org/mailman/listinfo/python-list
