braver wrote:
> Well, I know some python, but since there are powerful and magical
> features in it, I just wonder whether there're some which address this
> issue better than others.
>
In python, += is short, of course, for
a = a + 1
But if we haven't already assigned a, how does the interpreter know that
we want an int, float, complex, long, or some other data-type that
defines "+"?
Better, clearer or more pythonic would be:
a = 0.0 # we want a float, compiler didn't have to read mind
b = 0 # now we want an int, saving compiler lots of guesswork
a += 1 # incrementing a float by one
The "<<" operator corresponds to the __lshift__ magic method. You can
make a custom data-type here:
class lshiftinglist(list):
def __lshift__(self, value):
list.append(self, value)
class meh(dict):
def __getitem__(self, item):
return dict.setdefault(self, item, meh())
m = meh()
m['bob']['carol'] = 1
m['bob']['carol'] += 1
m['bob']['ted'] = lshiftinglist()
m['bob']['ted'] << 42
m['bob']['ted'] << 43
print m # {'bob': {'carol': 2, 'ted': [42, 43]}}
Other than magically reading mind of programmer, this works pretty much
according to specification.
If you really want a lot of mindreading abilities, you have to write
your own mindreading code. Here is a tiny example:
class meh(dict):
def __getitem__(self, item):
return dict.setdefault(self, item, meh())
def __getattr__(self, attr):
return self.ga(attr)
def __lshift__(self, value):
print "You are thinking of '%s'." % value
def __iadd__(self, other):
# don't try this on a populated meh!!!!!
return other
m = meh()
# mindreading way
m['carol'] += 4
m['carol'] += 5
m['bob'] << 44 # "You are thinking of '44'."
# better, not mindreading way
m['alice'] = [10]
m['alice'].append(11)
m['ted'] = 18
m['ted'] += 1
print m # "{'carol': 9, 'ted': 19, 'bob': {}, 'alice': [10, 11]}"
It would take a lot of coding to make that << work right. Better is the
pythonic
m[key] = [value]
Its really only one more keystroke than
m[key] << value
James
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