Roughly approximate the width of a string of text in Python?

Below is my simple solution, which gets you on the order of 80% accuracy, perfect for my purposes. It only works for Arial and it assumes 12 pt font, but it's probably proportional to other fonts as well.

def getApproximateArialStringWidth(st):
    size = 0 # in milinches
    for s in st:
        if s in 'lij|\' ': size += 37
        elif s in '![]fI.,:;/\\t': size += 50
        elif s in '`-(){}r"': size += 60
        elif s in '*^zcsJkvxy': size += 85
        elif s in 'aebdhnopqug#$L+<>=?_~FZT' + string.digits: size += 95
        elif s in 'BSPEAKVXY&UwNRCHD': size += 112
        elif s in 'QGOMm%W@': size += 135
        else: size += 50
    return size * 6 / 1000.0 # Convert to picas

And if you want to truncate a string, here it is:

def truncateToApproximateArialWidth(st, width):
    size = 0 # 1000 = 1 inch
    width = width * 1000 / 6 # Convert from picas to miliinches
    for i, s in enumerate(st):
        if s in 'lij|\' ': size += 37
        elif s in '![]fI.,:;/\\t': size += 50
        elif s in '`-(){}r"': size += 60
        elif s in '*^zcsJkvxy': size += 85
        elif s in 'aebdhnopqug#$L+<>=?_~FZT' + string.digits: size += 95
        elif s in 'BSPEAKVXY&UwNRCHD': size += 112
        elif s in 'QGOMm%W@': size += 135
        else: size += 50
        if size >= width:
            return st[:i+1]
    return st

Then the following:

>> width = 15
>> print truncateToApproxArialWidth("the quick brown fox jumps over the lazy dog", width) 
the quick brown fox jumps over the
>> print truncateToApproxArialWidth("THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG", width) 
THE QUICK BROWN FOX JUMPS

When rendered, those strings are roughly the same width:

the quick brown fox jumps over the

THE QUICK BROWN FOX JUMPS

You could render an image with the text using PIL and then determine the resulting image width.

http://effbot.org/imagingbook/imagefont.htm