5.1.7 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.

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