is there a better way...

[Mark McEahern]

[Christopher Encapera]
> Subject: is there a better way...
>
>
> to loop over a list and replace an element based on its value than:

There are three ways shown below, including your approach (replace).  Try
the script and see for yourself how each performs:

#! /usr/bin/env python

from time import clock
import random

def replace(l, old, new):
    # Make a copy.
    x = list(l)
    y = len(x)
    z = 0
    while z < y:
        element = x[z]
        if element == old: x[z] = new
        z = z +1
    return x

def replace_for(l, old, new):
    # Make a copy.
    x = list(l)
    for i in range(len(x)):
        if x[i] == old:
            x[i] = new
            break # use continue if we expect more than one match.
    return x

def replace_dict(l, old, new):
    d = dict(zip(l, l))
    d[old] = new
    return d.values()

def timeit(f, *args):
    time_in = clock()
    result = f(*args)
    time_out = clock()
    return result, time_out - time_in

size = 100000
x = range(size)

old = random.randrange(0, size)
new = "blueberry"

r1, t1 = timeit(replace, x, old, new)
r2, t2 = timeit(replace_dict, x, old, new)
r3, t3 = timeit(replace_for, x, old, new)

assert(r1==r2==r3)
print "replace: %0.3f" % t1
print "replace_dict: %0.3f" % t2
print "replace_for: %0.3f" % t3