Python Cookbook 2Nd Edition Jun 1002005 [Electronic resources] نسخه متنی

Recipe 1.1. Processing a String One Character at a Time

Credit: Luther Blissett

Problem

You want to process a string one character at a time.

Solution

You
can build a list whose items are the string's
characters (meaning that the items are strings, each of length of
onePython doesn't have a special type for
"characters" as distinct from
strings). Just call the built-in list, with the
string as its argument:

thelist = list(thestring)

You may not even need to build the list, since you can loop directly
on the string with a for statement:

for c in thestring:
do_something_with(c)

or in the for clause of a list comprehension:

results = [do_something_with(c) for c in thestring]

or, with exactly the same effects as this list comprehension, you can
call a function on each character with the map
built-in function:

results = map(do_something, thestring)

Discussion

In Python,
characters are just strings of length one. You can loop over a string
to access each of its characters, one by one. You can use
map for much the same purpose, as long as what you
need to do with each character is call a function on it. Finally, you
can call the built-in type list to obtain a list
of the length-one substrings of the string (i.e., the
string's characters). If what you want is a set
whose elements are the string's characters, you can
call sets.Set with the string as the argument (in
Python 2.4, you can also call the built-in set in
just the same way):

import sets
magic_chars = sets.Set('abracadabra')
poppins_chars = sets.Set('supercalifragilisticexpialidocious')
print ''.join(magic_chars & poppins_chars)   # set intersection
acrd

See Also

The Library Reference section on sequences;
Perl Cookbook Recipe 1.5.