How to fill elements between intervals of a list

Question

I have a list like this:

list_1 = [np.NaN, np.NaN, 1, np.NaN, np.NaN, np.NaN, 0, np.NaN, 1, np.NaN, 0, 1, np.NaN, 0, np.NaN,  1, np.NaN]

So there are intervals that begin with 1 and end with 0. How can I replace the values in those intervals, say with 1? The outcome will look like this:

list_2 = [np.NaN, np.NaN, 1, 1, 1, 1, 0, np.NaN, 1, 1, 0, 1, 1, 0, np.NaN, 1, np.NaN]

I use NaN in this example, but a generalized solution that can apply to any value will also be great

Answer 1

Pandas solution:

s = pd.Series(list_1)
s1 = s.eq(1)
s0 = s.eq(0)
m = (s1 | s0).where(s1.cumsum().ge(1),False).cumsum().mod(2).eq(1)
s.loc[m & s.isna()] = 1
print(s.tolist())
#[nan, nan, 1.0, 1.0, 1.0, 1.0, 0.0, nan, 1.0, 1.0, 0.0, 1.0, 1.0, 0.0, nan, 1.0, 1.0]

---

but if there is only 1, 0 or NaN you can do:

s = pd.Series(list_1)
s.fillna(s.ffill().where(lambda x: x.eq(1))).tolist()

output

[nan,
 nan,
 1.0,
 1.0,
 1.0,
 1.0,
 0.0,
 nan,
 1.0,
 1.0,
 0.0,
 1.0,
 1.0,
 0.0,
 nan,
 1.0,
 1.0]