Question

I know that I should use the access methods. I see in the datetime module that the class datetime inherits from date.

class datetime(date):
    <some other code here....>
    self = date.__new__(cls, year, month, day)
    self._hour = hour
    self._minute = minute
    self._second = second
    self._microsecond = microsecond
    self._tzinfo = tzinfo
    return self

I also see that datetime is able to access the members of date, as in __repr__:

def __repr__(self):
    """Convert to formal string, for repr()."""
    L = [self._year, self._month, self._day, # These are never zero
         self._hour, self._minute, self._second, self._microsecond]

I tried to subclass datetime to add some information to it and then write a similar __repr__ function:

def __repr__(self):
    """Convert to formal string, for repr()."""
    L = [self._year, self._month, self._day, # These are never zero
         self._hour, self._minute, self._second, self._microsecond,
         self._latitude, self._longitude]

The debugger complained that self._year didn’t exist. (self.year works, however.)

I know that I should be using the access function. I just want to understand why datetime is able to access the private variables of date but my subclass isn’t able.

Answer 1

if you look at the end of datetime.py, you’ll see this:

try:
    from _datetime import *
except ImportError:
    pass

this imports among other things the C-version of the previously defined python classes, which will therefore be used, and those don’t have the members you’re trying to access.