Character Translation using Python (like the tr command)

See string.translate

import string
"abc".translate(string.maketrans("abc", "def")) # => "def"

Note the doc's comments about subtleties in the translation of unicode strings.

And for Python 3, you can use directly:

str.translate(str.maketrans("abc", "def"))

Edit: Since tr is a bit more advanced, also consider using re.sub.

If you're using python3 translate is less verbose:

>>> 'abc'.translate(str.maketrans('ac','xy'))
'xby'

Ahh.. and there is also equivalent to tr -d:

>>> "abc".translate(str.maketrans('','','b'))
'ac' 

For tr -d with python2.x use an additional argument to translate function:

>>> "abc".translate(None, 'b')
'ac'