Speeding up datetime.strptime

datetime, profiling, python, python-2.7, strptime

Solution

Yes, there are faster methods to parse a date than `datetime.strptime()`, if you forgo a lot of flexibility and validation. `strptime()` allows both numbers with and without zero-padding, and it only matches strings that use the right separators, whilst your 'ugly' version doesn't.

You should always use the `timeit` module for time trials, it is far more accurate than `cProfile` here.

Indeed, your 'ugly' approach is twice as fast as `strptime()`:

>>> from datetime import date, datetime
>>> import timeit
>>> def ugly(input_date):
...     a= 1000 * int(input_date[0])
...     b=  100 * int(input_date[1])
...     c=   10 * int(input_date[2])
...     d=    1 * int(input_date[3])
...     year = a+b+c+d
...     c=   10 * int(input_date[5])
...     d=    1 * int(input_date[6])
...     month = c+d
...     c=   10 * int(input_date[8])
...     d=    1 * int(input_date[9])
...     day = c+d
...     try:
...         my_date = date(year, month, day)
...     except ValueError:
...         my_date = None
... 
>>> def strptime(input_date):
...     try:
...         my_date = datetime.strptime(input_date, "%Y-%m-%d").date()
...     except ValueError:
...         my_date = None
... 
>>> timeit.timeit('f("2014-07-08")', 'from __main__ import ugly as f')
4.21576189994812
>>> timeit.timeit('f("2014-07-08")', 'from __main__ import strptime as f')
9.873773097991943

Your approach can be improved upon though; you could use slicing:

>>> def slicing(input_date):
...     try:
...         year = int(input_date[:4])
...         month = int(input_date[5:7])
...         day = int(input_date[8:])
...         my_date = date(year, month, day)
...     except ValueError:
...         my_date = None
... 
>>> timeit.timeit('f("2014-07-08")', 'from __main__ import slicing as f')
1.7224829196929932

Now it is almost 6 times faster. I also moved the `int()` calls into the `try` - `except` to handle invalid input when converting strings to integers.

You could also use `str.split()` to get the parts, but that makes it slightly slower again:

>>> def split(input_date):
...     try:
...         my_date = date(*map(int, input_date.split('-')))
...     except ValueError:
...         my_date = None
... 
>>> timeit.timeit('f("2014-07-08")', 'from __main__ import split as f')
2.294667959213257

Problem

Original source