Huh. Never seen that. But without the [] it appears to produce a generator expression (which is immediately consumed) rather than a list (which is immediately

Huh. Never seen that. But without the [] it appears to produce a generator expression (which is immediately consumed) rather than a list (which is immediately consumed). In [9]: print ' '.join(str(x) for x in range(3)) 0 1 2 In [10]: type(str(x) for x in range(3)) Out[10]: generator In [11]: type([str(x) for x in range(3)]) Out[11]: list Same effect between the two, but different and interesting things. Thanks. EDIT: Also: In [3]: %timeit ' '.join(str(x) for x in range(3)) 100000 loops, best of 3: 3.11 µs per loop In [4]: %timeit ' '.join([str(x) for x in range(3)]) 1000000 loops, best of 3: 1.47 µs per loop The list version, with the [], is about twice as fast as the generator version (without the brackets). I suspect because the generator version has to "go back to the well" for each value, but I don't really know. And this is one small test case, maybe it's different for larger sequences. Testing is everything. :)