> Hi,
> I am little obssessed with my own coded after i
> found out it is slow. I am trying to construct a html
> table string from a result that i obtain from
> database.My code segment look like this: assume result
> holds 2D list.
> ******* method********************************
> def f1(item):
> return "<td>"+str(item)+"</td>"
> *****************************************
> ************main program piece***********
> tab = "<table align='center' border='1'>\n"
> for x in result:
> tab = tab + "<tr>"
> tab = tab + string.join(map(f1,x),"")+"</tr>\n"
> tab = tab + "</table>"
> print "Content-type:text/html\n"
> print tab
> **********************************************
> Can anyone improve this code segment? Thanks alot
The big problem is that tab=tab+"..." in a loop is expensive since
Python must allocate a new string and copy the old one each time. The
running time will increase with the square of the number of records,
i.e. O(n*n).
It may not be intuitive, but putting all the partial strings in a list
and then joining them at the end is more efficient as the running time
will increase only linearly with the number of records, i.e. O(n).
tab = []
tab.append("<table align='center' border='1'>\n")
for x in result:
tab.append("<tr>")
for y in x:
tab.extend(("<td>",y,"</td>\n"))
tab.append("</tr>")
tab.append("</table>")
print string.join(tab, "")
O(n) will always beat O(n*2) for large enough n, even if the individual
operations are slower.
Brent
