On Mon, Jul 13, 2009 at 2:08 PM, Dave Angel <da...@ieee.org> wrote: > Markus Hubig wrote: > >> Hi @all, >> >> within diveintopython I often found a for-statement like this: >> >> f for f in bla: >> print f >> >> So what actually is the first f for ... is it just to declare f before >> starting the for loop? I can't find any information on python.org >> and it's hard to google this kinda stuff. >> >> - Markus >> >> >> > Please give us a reference, as to exactly where you saw that. It gives a > syntax error in Python 2.62, as I expected it would. That's not how a for > statement works. > > > On the other hand, if you enclose that phrase in square brackets, it makes > a list comprehension. > > mylist = [f for f in bla] > > A list comprehension builds a new list, where the first pieces says what > goes into the list, and the second part describes how to generate it. In > this case, if bla is already a list, this just copies the list. But > consider > mylist = [f*f for f in bla] > > That builds a new list from the old, where each item is the square of the > corresponding old item. > > List comprehension is something you can look up in the help. Also look up > generator expression, which uses similar syntax. > > > DaveA >
Yes your right, the examples are enclosed in square brackets ... so this is the explanation I was looking for, thank you. And now I also found the explanation in diveintopython<http://diveintopython.org/native_data_types/mapping_lists.html>! ;-) - Markus -- -------------------"it's like this"------ even samurai have teddy bears and even teddy bears get drunk
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