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A comment on Python Practices for Efficient Code: Performance, Memory, and Usability. Parent comment

Re:Python Practices for Efficient Code: Performance, Memory,... by dom0 on Friday August 18, 2017 @05:19PM (#15049804)
The reason join is fast for these cases is because join basically converts all iterables to a list first and figures out how much it has to join exactly.
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Re:Python Practices for Efficient Code: Performance, Memory,... by dr_zoidberg on Monday August 21, 2017 @12:49PM (#15065836)
It walks the iterables (no need to convert them to lists), but its main trick is actually knowing how much memory it'll need for the end result, so no re-allocations happen, simply a one pass (through multiple iterables) copy.
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Re:Python Practices for Efficient Code: Performance, Memory,... by dom0 on Monday August 21, 2017 @04:54PM (#15067789)
No, it really converts all iterables to lists (there is a utility function in the C API to do just that, because it's kinda hairy to do by hand. PySequence_ToList or so). Otherwise it would not be possible to calculate how much space is required beforehand, since iterables cannot be walked twice.
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