字符串检查多种类型

Question

我有一个包含字符串的变量(从XML提要中提取).字符串值可以是整数,日期或字符串.我需要将它从字符串转换为给定的数据类型.我这样做,但它有点难看,所以我问是否有更好的技术.如果我要检查更多类型,我将以非常嵌套的try - except块结束.

def normalize_availability(self, value):
    """
    Normalize the availability date.
    """
    try:
        val = int(value)
    except ValueError:
        try:
            val = datetime.datetime.strptime(value, '%Y-%m-%d')
        except (ValueError, TypeError):
            # Here could be another try - except block if more types needed
            val = value

谢谢!

Answer 1

使用方便的助手功能.

def tryconvert(value, default, *types):
    """Converts value to one of the given types.  The first type that succeeds is
       used, so the types should be specified from most-picky to least-picky (e.g.
       int before float).  The default is returned if all types fail to convert
       the value.  The types needn't actually be types (any callable that takes a
       single argument and returns a value will work)."""
    value = value.strip()
    for t in types:
        try:
            return t(value)
        except (ValueError, TypeError):
            pass
    return default

然后编写一个函数来解析日期/时间:

def parsedatetime(value, format="%Y-%m-%d")
    return datetime.datetime.striptime(value, format)

现在把它们放在一起:

value = tryconvert(value, None, parsedatetime, int)