[prev in list] [next in list] [prev in thread] [next in thread] 

List:       python-list
Subject:    Re: I could use some help making this Python code run faster using
From:       Paul Hankin <paul.hankin () gmail ! com>
Date:       2007-09-20 22:46:53
Message-ID: 1190328413.226577.206740 () k79g2000hse ! googlegroups ! com
[Download RAW message or body]

On Sep 20, 10:59 pm, Python Maniac <raych...@hotmail.com> wrote:
> I am new to Python however I would like some feedback from those who
> know more about Python than I do at this time.
>
> def scrambleLine(line):
>     s = ''
>     for c in line:
>         s += chr(ord(c) | 0x80)
>     return s
>
> def descrambleLine(line):
>     s = ''
>     for c in line:
>         s += chr(ord(c) & 0x7f)
>     return s
> ...

Well, scrambleLine will remove line-endings, so when you're
descrambling
you'll be processing the entire file at once. This is particularly bad
because of the way your functions work, adding a character at a time
to
s.

Probably your easiest bet is to iterate over the file using read(N)
for some small N rather than doing a line at a time. Something like:

process_bytes = (descrambleLine, scrambleLine)[action]
while 1:
    r = f.read(16)
    if not r: break
    ff.write(process_bytes(r))

In general, rather than building strings by starting with an empty
string and repeatedly adding to it, you should use ''.join(...)

For instance...
def descrambleLine(line):
  return ''.join(chr(ord(c) & 0x7f) for c in line)

def scrambleLine(line):
  return ''.join(chr(ord(c) | 0x80) for c in line)

It's less code, more readable and faster!

--
Paul Hankin

-- 
http://mail.python.org/mailman/listinfo/python-list
[prev in list] [next in list] [prev in thread] [next in thread]