readTXT function

def readTXT(loc, fileName, sep, commentChar):
    import os
    import numpy as np

    # check inputs
    check = [os.path.isdir(loc), os.path.isfile(os.path.join(loc, fileName)), os.path.splitext(fileName)[1] in [".txt", ".asc"]]
    try:
        # Open file and readlines if line does not start with commentChar
        f = open(os.path.join(loc, fileName), "r")
        lines = [line.strip('\n') for line in f.readlines() if line[0] is not commentChar]

        # placeholders for array rows and the nr. of columns in each row
        rows = []
        colLengths = []

        # Verify the number of columns in each row
        for line in lines:
            colLengths.append(len([len(i) for i in line.split(sep) if len(i) is not 0]))

        # If all rows have equal number of columns
        if len(set(colLengths)) <= 1:
            # Add each line to the rows list
            for line in lines:
                rows.append([int(i) for i in line.split(sep)])
            # Vertical stack the all rows into an array
            out = np.vstack(tuple(rows))
        else:
            raise ValueError("Number of columns is not equal over the input array: {0}".format(colLengths))
        return out

    except (RuntimeError, IOError) as e:
        print "Something went wrong, check the following: {0}".format(zip(["Valid Directory?", "Valid filename?", "Valid file extension?"], check))