Pulling numbers from ASCII filename not working

[IamIan]

I searched the archives but couldn't find anyone else with this
problem. Basically I'm grabbing all ASCII files in a directory and
doing geoprocessing on them. I need to calculate a z-factor based on
the latitude of the ASCII file being worked on, which is in the
filename. If I type in the code manually it works and reads the
latitude value from the ASCII filename, but when run within ArcGIS it
crashes when it gets to int(LatString). Isnumber() returned false for
Latitude as well. Is there something different about reading values
from an ASCII filename?

import sys, os, win32com.client, string, gc

# Get a list of ASCII files in the workspace for ASCII To Raster
conversion
filenames = os.listdir(gp.workspace)
filenames = [filename.lower()
for filename in filenames
if (filename[-4:].lower() == ".asc" and filename[0] != "-" )]
for filename in filenames:

        # For each ASCII file, create Hillshade.
        # account for latitude by computing Z units using radians
        Latitude = filename[1:3]
        LatString = str(Latitude)
        LatInt = int(LatString)
        radians = LatInt * 0.0174532925
        zFactor = 1/(113200 * (cos(radians)))