Python 对文件中合法数字进行求和 (try...except)

def safe_float(obj):
    'safe version of float()'
    try:
        retval = float(obj)
    except (ValueError, TypeError), diag:
        retval = str(diag)
    return retval

def data_process_handler():
    log = open('cardlog.txt', 'w')
    try:
        ccfile = open('carddata.txt', 'r')
    except IOError, e:
        log.write('no txns this month\n')
        log.close()
        return

    txns = ccfile.readlines()
    ccfile.close()
    total = 0.00
    log.write('account log:\n')

    for eachTxn in txns:
        result = safe_float(eachTxn)
        if isinstance(result, float):
            total += result
            log.write('data... processed\n')
        else:
            log.write('ignored: %s' % result)
    print '$%.2f (new balance)' % (total)
    log.close()

if __name__ == '__main__':
    data_process_handler()

In [7]: data_process_handler()
$58.94 (new balance)

In [8]: !more carlog.txt
account log:
ignored: could not convert string to float: previous balance
data... processed
ignored: could not convert string to float: debits
data... processed
data... processed
data... processed
ignored: could not convert string to float: credits
data... processed
data... processed
ignored: could not convert string to float: finance charge/late fees
data... processed
data... processed

cat carddata.txt
previous balance
25
debits
21.64
541.24
25
credits
-25
-541.24
finance charge/late fees
7.30
5