From pep-0008:
```
Always use a def statement instead of an assignment statement that binds a
lambda expression directly to an identifier.
Yes:
def f(x): return 2*x
No:
f = lambda x: 2*x
The first form means that the name of the resulting function object is
specifically 'f' instead of the generic '<lambda>'. This is more useful for
tracebacks and string representations in general. The use of the assignment
statement eliminates the sole benefit a lambda expression can offer over an
explicit def statement (i.e. that it can be embedded inside a larger expression)
```
- Use parameter_space instead of `parameterized.expand`.
- Use a timedelta instead of concatenating strings.
- Use a (possibly no-op) scramble function instead of reordering list
literals.
- Use `freeze_dt, unfreeze_dt, re_freeze_dt` instead of `dts[n]`.
- Rename `assert_vectorized_results` to `assert_all_restrictions`.
The SecurityList implements a non-exposed method
`current_securities(dt)` which SecurityListRestrictions calls to
determine if an asset is restricted. Deprecate the `__iter__` and
`__contains__` methods of security lists in favor of
`current_securities(dt)`
An ABC Restrictions defines a group of restrictions responsible
for returning restriction information for sids on certain dts. An
InMemoryRestrictions is a point-in-time group of such restrictions,
with all restrictions and their dates passed in upon instantiation.
A StaticRestrictedList takes a list of sids, restricting them at all
dates
Conner Fromknecht