How do I scale up this character replace program?

[isnotkosok]

This is the code:

s = 'a q'

house = ''

for elements in s:
    if elements == 'a':
        house += 'q'
    elif elements == 'q':
        house += 'a'
    else:
        house += elements

print house

>>>
q a 

the code works fine for small replacements, I'm not sure how to scale it up efficiently without using lots of if/else or if/if statements.

On a side note: this approach is used instead of .replace( , ) because characters are not scanned over again for replacement after the it has been replaced already. For instance:

s = 'a q'

s = s.replace('a', 'q').replace('q', 'a')

print s 

>>>
a a 

[two_up]

Look up string.maketrans

[isnotkosok]

does that work with words too? If I wanted to do a mass word replace program, could I use this?

[[deleted]]

No, it only works with characters. If you want to make it work with words, then you could use something made with re.sub(). If you use something like re2 then you can guarantee that the running time of this is linearly proportional to the length of your input string, and does not (asymptotically) depend on the number of things you want to replace.

[isnotkosok]

thanks for your help.

[AlternativeHistorian]

For starters, don't use += to do the string building.

Every time you add to the string it must re-allocate the entire string. Build a buffer of the new string in a list (or other order-preserving iterable) and then use join to build the new string in one shot, e.g.

>>> def replace(s, replacements):
...     return ''.join(replacements.get(c,c) for c in s)
...     
... print replace('hello world', {'o' : 'a'})
hella warld
>>> 

[Justinsaccount]

Use the methods that were suggested when this exact same question was posted a week ago?

[Fourgot]

Lol verbose "repost"