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Doc: Try to enhance wording on circular imports. (GH-24705)

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Julien Palard 2021-04-13 18:03:22 +02:00 committed by GitHub
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Doc/faq/programming.rst
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@ -1898,26 +1898,26 @@ How can I have modules that mutually import each other?
Suppose you have the following modules:
foo.py::
:file:`foo.py`::
from bar import bar_var
foo_var = 1
bar.py::
:file:`bar.py`::
from foo import foo_var
bar_var = 2
The problem is that the interpreter will perform the following steps:
* main imports foo
* Empty globals for foo are created
* foo is compiled and starts executing
* foo imports bar
* Empty globals for bar are created
* bar is compiled and starts executing
* bar imports foo (which is a no-op since there already is a module named foo)
* bar.foo_var = foo.foo_var
* main imports ``foo``
* Empty globals for ``foo`` are created
* ``foo`` is compiled and starts executing
* ``foo`` imports ``bar``
* Empty globals for ``bar`` are created
* ``bar`` is compiled and starts executing
* ``bar`` imports ``foo`` (which is a no-op since there already is a module named ``foo``)
* The import mechanism tries to read ``foo_var`` from ``foo`` globals, to set ``bar.foo_var = foo.foo_var``
The last step fails, because Python isn't done with interpreting ``foo`` yet and
the global symbol dictionary for ``foo`` is still empty.