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The string join method can concatenate strings significantly faster than using the '+' operator. I think Raymond Hettinger talked about this in one of his presentations archived on pyvideo.org.



In [1]:

    
width = 1000



In [2]:

    
def foo(width):
    horizontal_line = '{'
    for i in range(width):
        horizontal_line += (' ' + '#ffffff')
    horizontal_line += '}'



In [3]:

    
%timeit foo(width)









    



1000 loops, best of 3: 210 µs per loop



In [4]:

    
def foo(width):
    horizontal_line = (
        '{' +
        ' '.join(
            '#ffffff' for i in range(width)
        ) +
        '}'
    )



In [5]:

    
%timeit foo(width)









    



10000 loops, best of 3: 129 µs per loop



In [6]:

    
def foo(width):
    horizontal_line = ''.join([
        '{',
        ' '.join(
            '#ffffff' for i in range(width)
        ),
        '}',
    ])



In [7]:

    
%timeit foo(width)









    



10000 loops, best of 3: 129 µs per loop