My QueryList is simple to use.
ql.filter(portfolio='123')
ql.group_by(['portfolio', 'ticker'])
class QueryList(list):
"""filter and/or group_by a list of objects."""
def group_by(self, attrs) -> dict:
"""Like a database group_by function.
args:
attrs: str or list.
Returns:
{value_of_the_group: list_of_matching_objects, ...}
When attrs is a list, each key is a tuple.
Ex:
{'AMZN': QueryList(),
'MSFT': QueryList(),
...
}
-- or --
{('Momentum', 'FB'): QueryList(),
...,
}
"""
result = defaultdict(QueryList)
if isinstance(attrs, str):
for item in self:
result[getattr(item, attrs)].append(item)
else:
for item in self:
result[tuple(getattr(item, x) for x in attrs)].append(item)
return result
def filter(self, **kwargs):
"""Returns the subset of IndexedList that has matching attributes.
args:
kwargs: Attribute name/value pairs.
Example:
foo.filter(portfolio='123', account='ABC').
"""
ordered_kwargs = OrderedDict(kwargs)
match = tuple(ordered_kwargs.values())
def is_match(item):
if tuple(getattr(item, y) for y in ordered_kwargs.keys()) == match:
return True
else:
return False
result = IndexedList([x for x in self if is_match(x)])
return result
def scalar(self, default=None, attr=None):
"""Returns the first item in this QueryList.
args:
default: The value to return if there is less than one item,
or if the attr is not found.
attr: Returns getattr(item, attr) if not None.
"""
item, = self[0:1] or [default]
if attr is None:
result = item
else:
result = getattr(item, attr, default)
return result
I tried pandas. I wanted to like it, I really did. But ultimately it is too complicated for my needs.
For example:
df[df['portfolio'] == '123'] & df['ticker'] == 'MSFT']]
is not as simple as
ql.filter(portfolio='123', ticker='MSFT')
Furthermore, creating a QueryList is simpler than creating a df.
That's because you tend to use custom classes with a QueryList. The data conversion code would naturally be placed into the custom class which keeps that separate from the rest of the logic. But data conversion for a df would normally be done inline with the rest of the code.
