## 6.9.7 `strftime()` Behavior

`date`, `datetime`, and `time` objects all support a `strftime(format)` method, to create a string representing the time under the control of an explicit format string. Broadly speaking, `d.strftime(fmt)` acts like the `time` module's `time.strftime(fmt, d.timetuple())` although not all objects support a `timetuple()` method.

For `time` objects, the format codes for year, month, and day should not be used, as time objects have no such values. If they're used anyway, `1900` is substituted for the year, and `0` for the month and day.

For `date` objects, the format codes for hours, minutes, and seconds should not be used, as `date` objects have no such values. If they're used anyway, `0` is substituted for them.

For a naive object, the `%z` and `%Z` format codes are replaced by empty strings.

For an aware object:

`%z`
  `utcoffset()` is transformed into a 5-character string of the form +HHMM or -HHMM, where HH is a 2-digit string giving the number of UTC offset hours, and MM is a 2-digit string giving the number of UTC offset minutes. For example, if `utcoffset()` returns `timedelta(hours=-3, minutes=-30)`, `%z` is replaced with the string `'-0330'`.

`%Z`
  If `tzname()` returns `None`, `%Z` is replaced by an empty string. Otherwise `%Z` is replaced by the returned value, which must be a string.

The full set of format codes supported varies across platforms, because Python calls the platform C library's `strftime()` function, and platform variations are common. The documentation for Python's `time` module lists the format codes that the C standard (1989 version) requires, and those work on all platforms with a standard C implementation. Note that the 1999 version of the C standard added additional format codes.

The exact range of years for which `strftime()` works also varies across platforms. Regardless of platform, years before 1900 cannot be used.