使用字符串变量格式化timedelta

Question

Using Python 2.6

Given the following line of code, how can I dynamically build the value for timedelta from variables in a DB?

next_alert_date = datetime.strptime(start_due_date, '%Y-%m-%d') + timedelta(days=2)

Basically, I need something like this but it doesnt appear to work.

SyntaxError: invalid syntax

next_alert_date = datetime.strptime(start_due_date, '%Y-%m-%d') + timedelta(%s=%d) % (interval_type, interval_num)

Answer 1

Maybe you're misunderstanding % operator used for string formatting operation ; it is used to make a string.

>>> 'timedelta(%s=%d)' % ('days', 2)
'timedelta(days=2)'

Use ** operator to pass keyword arguments dynamically:

>>> datetime.timedelta(**{'days': 2})
datetime.timedelta(2)

>>> interval_type = 'days'
>>> interval_num = 2
>>> datetime.timedelta(**{interval_type: interval_num})
datetime.timedelta(2)