Python Cookbook 2Nd Edition Jun 1002005 [Electronic resources]

Recipe 1.2. Converting Between Characters and Numeric Codes

Credit: Luther Blissett

Problem

You need to turn a character into its numeric ASCII (ISO) or Unicode code, and vice versa.

Solution

That's what the built-in functions ord and chr are for:

>>> print ord('a')
97
>>> print chr(97)
a

The built-in function ord also accepts as its argument a Unicode string of length one, in which case it returns a Unicode code value, up to 65536. To make a Unicode string of length one from a numeric Unicode code value, use the built-in function unichr:

>>> print ord(u'\u2020')
8224
>>> print repr(unichr(8224))
u'\u2020'

Discussion

It's a mundane task, to be sure, but it is sometimes useful to turn a character (which in Python just means a string of length one) into its ASCII or Unicode code, and vice versa. The built-in functions ord, chr, and unichr cover all the related needs. Note, in particular, the huge difference between chr(n) and str(n), which beginners sometimes confuse...:

>>> print repr(chr(97))
'a'
>>> print repr(str(97))
'97'

chr takes as its argument a small integer and returns the corresponding single-character string according to ASCII, while str, called with any integer, returns the string that is the decimal representation of that integer.

To turn a string into a list of character value codes, use the built-in functions map and ord together, as follows:

>>> print map(ord, 'ciao')
[99, 105, 97, 111]

To build a string from a list of character codes, use ''.join, map and chr; for example:

>>> print ''.join(map(chr, range(97, 100)))
abc

See Also

Documentation for the built-in functions chr, ord, and unichr in the Library Reference and Python in a Nutshell.