A fast datetime parser written in Python with minimal validations.

parse_datetime.py

import datetime

def parse_datetime(s):
    """Parse a datetime string with minimal validations.

    `parse_datetime` takes a string with format yyyy-mm-dd HH:MM:SS.zzzzzz
    and returns a `datetime.datetime` object. Any prefix of that format is
    accepted as well; so a string like "2017-12-22" will return a datetime
    with hour, mins, secs and microsecs set to zero.

    The microsecs part may have any length, but it will be truncated if
    there are more than 6 digits. Any non-digit character is considered a
    separator; so "xx 2017x12x22  13%50%45 %%", for example, is a valid
    date. Actual validation of date parts is left to `datetime.datetime`'s
    constructor (raises ValueError on invalid input).

    Args:
        s (string): the input string.

    Returns:
        A `datetime.datetime` object.
    """
def parse_datetime(s):
    s = s + ' '
    parts = [0, 0, 0, 0, 0, 0, 0]
    i, left = 0, 0
    is_sep = True
    for right in range(len(s)):
        c = s[right]
        if c >= '0' and c <= '9':
            if is_sep:
                is_sep = False
                left = right
        else:
            if not is_sep:
                is_sep = True
                v = int(s[left:right])
                d = right - left
                if i == 6:
                    v = v * 10 ** (6 - d) if d <= 6 else v / 10 ** (d - 6)
                parts[i] = v
                i += 1
        if i >= 7:
            break
    return datetime.datetime(*parts)