How can i show an input box when debugging using pdb?

When i try to debug with `from IPython.core.debugger import Pdb; Pdb().set_trace()` or `import ipdb; ipdb.set_trace()`, jupyter doesn't show an input box for debugging. Even if I restart kernel and run the code again, it doesn't show the input box. Here is the cell output.

I was expecting like this.

> For those reproducing this:
>
> ```python
> def my_sum(initnum, step, n):
> x = initnum
> from IPython.core.debugger import Pdb; Pdb().set_trace()
> for i in range(n):
> x = x + step
> return x
> my_sum(10, 2, 3)
> ```

When i try this on jupyter lab, it worked! but when i store the code in a file and ran `!python pdb_test.py` , it didn't show an input box.

but running py file with the code :/

pdb_test.py

Here is my environment
```

conda list ipython
# packages in environment at /home/zzz/anaconda3:
#
# Name Version Build Channel
ipython 6.1.0 py36hc72a948_1
ipython_genutils 0.2.0 py36hb52b0d5_0

```

```
jupyter-lab --version
3.0.5
```
ubuntu 18.04

Google Chrome
Version 88.0.4324.96 (Official Build) (64-bit)

I posted this issue first here **https://github.com/jupyterlab/jupyterlab/issues/9691**