datetime-fromisoformat.md

datetime-fromisoformat

The fromisoformat(x: str) from stdlib datetime type is very useful to parse dates from machine-generated timestamps. However it is often overlooked that it is only part of the stdlib module since python 3.7.

When fromisoformat is found in the code then the transformer will add some boilerplate code under the name datetime_fromisoformat. When the script is run under python 3.7 or later then the function is just calling the stdlib datetime.fromisoformat. If the datetime.datime module has already been imported but under a different name then that name is going to be used as the prefix.

    # original
    import datetime.datetime as Time
    def func1(x: x) -> Time:
        return Time.fromisoformat(x)

    # transformed
    import sys
    import datetime.datetime as Time
    if sys.version_info >= (3, 7):

        def Time_fromisoformat(x):
            return Time.fromisoformat(x)
    else:
    
        def Time_fromisoformat(x):
            import re
            m = re.match('(\\\\d\\\\d\\\\d\\\\d)-(\\\\d\\\\d)-(\\\\d\\\\d).(\\\\d\\\\d):(\\\\d\\\\d):(\\\\d\\\\d).(\\\\d\\\\d\\\\d\\\\d\\\\d\\\\d)', x)
            if m:
                return Time(int(m.group(1)), int(m.group(2)), int(m.group(3)), int(m.group(4)), int(m.group(5)), int(m.group(6)), int(m.group(7)))
            m = re.match('(\\\\d\\\\d\\\\d\\\\d)-(\\\\d\\\\d)-(\\\\d\\\\d).(\\\\d\\\\d):(\\\\d\\\\d):(\\\\d\\\\d).(\\\\d\\\\d\\\\d)', x)
            if m:
                return Time(int(m.group(1)), int(m.group(2)), int(m.group(3)), int(m.group(4)), int(m.group(5)), int(m.group(6)), int(m.group(7)) * 1000)
            m = re.match('(\\\\d\\\\d\\\\d\\\\d)-(\\\\d\\\\d)-(\\\\d\\\\d).(\\\\d\\\\d):(\\\\d\\\\d):(\\\\d\\\\d)', x)
            if m:
                return Time(int(m.group(1)), int(m.group(2)), int(m.group(3)), int(m.group(4)), int(m.group(5)), int(m.group(6)))
            m = re.match('(\\\\d\\\\d\\\\d\\\\d)-(\\\\d\\\\d)-(\\\\d\\\\d).(\\\\d\\\\d):(\\\\d\\\\d)', x)
            if m:
                return Time(int(m.group(1)), int(m.group(2)), int(m.group(3)), int(m.group(4)), int(m.group(5)))
            m = re.match('(\\\\d\\\\d\\\\d\\\\d)-(\\\\d\\\\d)-(\\\\d\\\\d)', x)
            if m:
                return Time(int(m.group(1)), int(m.group(2)), int(m.group(3)))
            raise ValueError('not a datetime isoformat: ' + x)
    
    def func1(x):
        return Time_fromisoformat(x)

Note that if a --python-version of 3.7 or later is selected then this transformer will not be executed at all.