escaping - Getting correct string length in Python for strings with ANSI color codes

Question

I've got some Python code that will automatically print a set of data in a nice column format, including putting in the appropriate ASCII escape sequences to color various pieces of the data for readability.

I eventually end up with each line being represented as a list, with each item being a column that is space-padded so that the same columns on each line are always the same length. Unfortunately when I actually go to print this, not all the columns line up. I suspect this is to do with the ASCII escape sequences - because the len function doesn't seem to recognize these:

>>> a = 'x1b[1m0.0x1b[0m'
>>> len(a)
11
>>> print a
0.0

And so while each column is the same length according to len, they are not actually the same length when printed on the screen.

Is there any way (save for doing some hackery with regular expressions which I'd rather not do) to take the escaped string and find out what the printed length is so I can space pad appropriately? Maybe some way to just "print" it back to string and examine the length of that?

Answer 1

The pyparsing wiki includes this helpful expression for matching on ANSI escape sequences:

ESC = Literal('x1b')
integer = Word(nums)
escapeSeq = Combine(ESC + '[' + Optional(delimitedList(integer,';')) + 
                oneOf(list(alphas)))

Here's how to make this into an escape-sequence-stripper:

from pyparsing import *

ESC = Literal('x1b')
integer = Word(nums)
escapeSeq = Combine(ESC + '[' + Optional(delimitedList(integer,';')) + 
                oneOf(list(alphas)))

nonAnsiString = lambda s : Suppress(escapeSeq).transformString(s)

unColorString = nonAnsiString('x1b[1m0.0x1b[0m')
print unColorString, len(unColorString)

prints:

0.0 3