Hello

I’m getting an error when passing multiple sequences to `aesara.scan`

:

```
import aesara
import pymc as pm
import numpy as np
for module in aesara, pm, np:
print(module.__name__, module.__version__)
# Generate some dummy data
m = 42
n = 8
g = np.random.randint(1, 5, (m, n))
y = np.random.uniform(size=(m, n))
with pm.Model():
p = pm.Beta("p", alpha=1, beta=100)
i = pm.Bernoulli("i", p, size=(m, n)) * 1.0
rho = pm.Beta("r", alpha=10, beta=1)
y0 = aesara.tensor.zeros(m)
mu, _ = aesara.scan(
lambda i, g, y, rho: rho**g * y + i,
sequences=[i.T, g.T],
outputs_info=y0,
non_sequences=[rho],
)
sigma = pm.Exponential("sigma", 1)
pm.Normal("y_hat", mu=mu.T, sigma=sigma, observed=y)
pm.sample()
```

```
aesara 2.8.7
pymc 4.3.0
numpy 1.23.4
Traceback (most recent call last):
File "/Users/pattinson/djpiri/content/Notes/2022-10-31-aesara-bug/main.py", line 21, in <module>
mu, _ = aesara.scan(
File "/Users/pattinson/.virtualenvs/pymc-fresh-env/lib/python3.10/site-packages/aesara/scan/basic.py", line 681, in scan
scan_seqs = [seq[:actual_n_steps] for seq in scan_seqs]
File "/Users/pattinson/.virtualenvs/pymc-fresh-env/lib/python3.10/site-packages/aesara/scan/basic.py", line 681, in <listcomp>
scan_seqs = [seq[:actual_n_steps] for seq in scan_seqs]
TypeError: slice indices must be integers or None or have an __index__ method
```

A similar model with only a single sequence (removing `g`

) samples fine:

```
with pm.Model():
p = pm.Beta("p", alpha=1, beta=100)
i = pm.Bernoulli("i", p, size=(m, n)) * 1.0
rho = pm.Beta("r", alpha=10, beta=1)
y0 = aesara.tensor.zeros(m)
mu, _ = aesara.scan(
lambda i, y, rho: rho * y + i,
sequences=[i.T],
outputs_info=y0,
non_sequences=[rho],
)
sigma = pm.Exponential("sigma", 1)
pm.Normal("y_hat", mu=mu.T, sigma=sigma, observed=y)
pm.sample()
```

Is this a problem with aesara? Or have I misunderstood something?

Thanks a lot

David