How do I reset the IPython input prompt numbering? (console, not notebook or qt) - ipython

Question

The following is my current IPython command prompt (regular terminal IPython, not the notebook, or Qt):
In [45]:
I'm done with my workflow, and am moving on to a new task. I'd like a way to reset the IPython input prompt number as follows:
In [1]:
I understand this may be possible from non-duplicate question to which I cannot reply nor answer for my case: How do I reset the IPython input prompt numbering?
For further clarity, an example of the command I'm after:
In [99]: %reset_command_number
In [1]: 2+2
Out[1]: 4
In [2]: %reset_command_number
In [1]:
The 3 Magic Questions:
Does such magic (%reset_command_number) exist?
If the answer to 1 is yes, what dark magic is it?
If the answer to 1 is no, is this achievable from a lower level IPython api? (yes i've searched the api docs and no i did not find a way to do it, yet...)

Answer 1

One possibility would be to modify the execution_count of the InteractiveShell:
import IPython; IPython.get_ipython().execution_count = 0
Using a one line command with ; makes it easier to call this repeatedly (if you use up-arrow to scroll the command history)
This has the side effect that after first command you will also see this error. I do not know if it has any side effects, though. (it already says that the history logging was moved to another session)
ERROR! Session/line number was not unique in database. History logging moved to new session 20741
Demo
In [1]: a = 1
In [2]: b = 88
In [3]: c = 99
In [4]: import IPython; IPython.get_ipython().execution_count = 0
In [1]: a
Out[1]: 1
ERROR! Session/line number was not unique in database. History logging moved to new session 20767
In [2]: b
Out[2]: 88
In [3]: c
Out[3]: 99
In [4]: import IPython; IPython.get_ipython().execution_count = 0
In [1]: a = 15
ERROR! Session/line number was not unique in database. History logging moved to new session 20768
In [2]: a
Out[2]: 15
In [3]: b
Out[3]: 88
Using an alias?
It is also possible to use an alias for the command. For example, create file i_reset.py and put it into your site-packages, ~/.ipython/extensions/, your PYTHONPATH or any other folder you can see in your sys.path
# i_reset.py
def i_reset(line):
"""
Reset IPython shell numbering to [1]
"""
import IPython; IPython.get_ipython().execution_count = 0
def load_ipython_extension(ipython):
"""This function is called when the extension is
loaded. It accepts an IPython InteractiveShell
instance. We can register the magic with the
`register_magic_function` method of the shell
instance."""
ipython.register_magic_function(i_reset, 'line')
Then, you may use the extension by first loading it and then calling it like so:
In [4]: %load_ext i_reset
In [5]: i_reset
In [1]: a
Out[1]: 1

Answer 2

I'm not sure you can, and what is done with the notebook is equivalent (from what I understood) to just open a new python session as if you open a new tab and start ipython again, and re-execute everything.
So, if I were you and had to start a new task and want to start at In [1] I would just start a new ipython environment.
The equivalent with ipython notebook to start a new task would be to start a new notebook.
The only reason I can imagine why you would do this is that you want to access some variable from the previous task.
What I would is to save the object you want to re-use using pickle or by saving a variable into a file an reload it in a new ipython session.
Did you looked at the Doc on Input caching system ? You may have answer to other question relative to yours.
Note that I'm aware that's not really an answer, but it's a bit more than just a comment, anyway, I hope this helps !
If you have more specific needs than just reseting the prompt number, just detail them.

Answer 3

Assuming you don't need the session data, the simplest is to exit and restart IPython.
$ ipython
In [1]: 1+1
Out[1]: 2
In [2]: 2+2
Out[2]: 4
In [3]: 3+3
Out[3]: 6
In [4]: exit
$ ipython
In [1]: print("Prompt numbering reset")
Prompt numbering reset
In [2]: