Tips for accelarating python programs

1.Use join instead of + to concentrate strings.
In python, string is unchangable. Each time you add a segment to existed string, it will re-create memeory to save new string. Thus, old string will be copy-paste for many times (No. of seg – 1).

2.Use local variable

#list = []
#for i in xrange(100):
#    list.append(i)
#
list = []
append = list.append
for i in xrange(100):
    append(i)
#or
list = [i for i in xrange(400)]

3.Use array from stdlib array instead of list when dealing with homogeneous data (all same type). This would save some memory.

from array import array
list = array()
append = list.append
for i in xrange(100):
    append(i)

4.