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Diffstat (limited to 'Doc/faq/programming.rst')
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diff --git a/Doc/faq/programming.rst b/Doc/faq/programming.rst index d1a3daf..f157a94 100644 --- a/Doc/faq/programming.rst +++ b/Doc/faq/programming.rst @@ -989,6 +989,32 @@ What does 'UnicodeDecodeError' or 'UnicodeEncodeError' error mean? See the :ref:`unicode-howto`. +What is the most efficient way to concatenate many strings together? +-------------------------------------------------------------------- + +:class:`str` and :class:`bytes` objects are immutable, therefore concatenating +many strings together is inefficient as each concatenation creates a new +object. In the general case, the total runtime cost is quadratic in the +total string length. + +To accumulate many :class:`str` objects, the recommended idiom is to place +them into a list and call :meth:`str.join` at the end:: + + chunks = [] + for s in my_strings: + chunks.append(s) + result = ''.join(chunks) + +(another reasonably efficient idiom is to use :class:`io.StringIO`) + +To accumulate many :class:`bytes` objects, the recommended idiom is to extend +a :class:`bytearray` object using in-place concatenation (the ``+=`` operator):: + + result = bytearray() + for b in my_bytes_objects: + result += b + + Sequences (Tuples/Lists) ======================== |