Siarhei Siniak
1530fcf108
1. 7f51a0332edd0c675c2d314ca3e62df7ef041281 deps/ipython (8.4.0-33-g7f51a0332)
73 lines
2.7 KiB
ReStructuredText
73 lines
2.7 KiB
ReStructuredText
.. _execution_semantics:
|
|
|
|
Execution of cells in the IPython kernel
|
|
========================================
|
|
|
|
When IPython kernel receives `execute_request <https://jupyter-client.readthedocs.io/en/latest/messaging.html#execute>`_
|
|
with user code, it processes the message in the following phases:
|
|
|
|
1. Fire the ``pre_execute`` event.
|
|
2. Fire the ``pre_run_cell`` event unless silent is ``True``.
|
|
3. Execute ``run_cell`` method to preprocess ``code``, compile and run it, see below for details.
|
|
4. If execution succeeds, expressions in ``user_expressions`` are computed.
|
|
This ensures that any error in the expressions don't affect the main code execution.
|
|
5. Fire the ``post_execute`` event.
|
|
6. Fire the ``post_run_cell`` event unless silent is ``True``.
|
|
|
|
.. seealso::
|
|
|
|
:doc:`/config/callbacks`
|
|
|
|
|
|
Running user ``code``
|
|
=====================
|
|
|
|
First, the ``code`` cell is transformed to expand ``%magic`` and ``!system``
|
|
commands by ``IPython.core.inputtransformer2``. Then expanded cell is compiled
|
|
using standard Python :func:`compile` function and executed.
|
|
|
|
Python :func:`compile` function provides ``mode`` argument to select one
|
|
of three ways of compiling code:
|
|
|
|
*single*
|
|
Valid for a single interactive statement (though the source can contain
|
|
multiple lines, such as a for loop). When compiled in this mode, the
|
|
generated bytecode contains special instructions that trigger the calling of
|
|
:func:`sys.displayhook` for any expression in the block that returns a value.
|
|
This means that a single statement can actually produce multiple calls to
|
|
:func:`sys.displayhook`, if for example it contains a loop where each
|
|
iteration computes an unassigned expression would generate 10 calls::
|
|
|
|
for i in range(10):
|
|
i**2
|
|
|
|
*exec*
|
|
An arbitrary amount of source code, this is how modules are compiled.
|
|
:func:`sys.displayhook` is *never* implicitly called.
|
|
|
|
*eval*
|
|
A single expression that returns a value. :func:`sys.displayhook` is *never*
|
|
implicitly called.
|
|
|
|
|
|
The ``code`` field is split into individual blocks each of which is valid for
|
|
execution in 'single' mode, and then:
|
|
|
|
- If there is only a single block: it is executed in 'single' mode.
|
|
|
|
- If there is more than one block:
|
|
|
|
* if the last block is a single line long, run all but the last in 'exec' mode
|
|
and the very last one in 'single' mode. This makes it easy to type simple
|
|
expressions at the end to see computed values.
|
|
|
|
* if the last block is no more than two lines long, run all but the last in
|
|
'exec' mode and the very last one in 'single' mode. This makes it easy to
|
|
type simple expressions at the end to see computed values. - otherwise
|
|
(last one is also multiline), run all in 'exec' mode
|
|
|
|
* otherwise (last block is also multiline), run all in 'exec' mode as a single
|
|
unit.
|
|
|
|
|