How to Index Pandas Dataframe with a List of Slices - pandas

Question

I have two data frames, ret and bins. I would like to take index values from bins, create a range for every row in bins and then use that list of ranges to select the data from ret. Somehow this works when I pass an index of slices (manually typed in), but doesn't work when I pass in a list saved in the variable a
ret = pd.DataFrame({'px': [.1, -.15, .30, -.20, .05]})
bins = pd.DataFrame({'t1': [3,4]}, index=[1,2])
a = []
for i, b in bins.iterrows():
a.append(slice(i, b.t1))
print('a',a)
print('np.r_[a]',np.r_[a])
print('np.r[slice',np.r_[slice(1, 3, None) , slice(1, 4, None)])
print(ret.iloc[np.r_[slice(1, 3, None) , slice(1, 4, None)]]) # this WORKS
print(ret.iloc[a] #this DOES NOT WORK)
here is the output:
a [slice(1, 3, None), slice(2, 4, None)]
np.r_[a] [slice(1, 3, None) slice(2, 4, None)]
np.r[slice [1 2 1 2 3]
px
1 -0.15
2 0.30
1 -0.15
2 0.30
3 -0.20
...
TypeError: int() argument must be a string, a bytes-like object or a number, not 'slice'

Answer 1

Going to answer my own question here! Problem was slice() is too cumbersome to use. Easier to just flatten the lists of arrays. If anyone has any suggestions please post here!
ret = pd.DataFrame({'px': [.1, -.15, .30, -.20, .05]})
bins = pd.DataFrame({'t1': [3,4]}, index=[1,2])
a = [ret[i:b.t1].index for i, b in bins.iterrows()]
out = [item for sublist in a for item in sublist]
print(ret.loc[out])
>>> px
>>>1 -0.15
>>>2 0.30
>>>2 0.30
>>>3 -0.20