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Re: Cyclic imports

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From: ros...@gmail.com (Chris Angelico)
Newsgroups: comp.lang.python
Subject: Re: Cyclic imports
Date: Wed, 18 Aug 2021 04:19:51 +1000
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<11811693.O9o76ZdvQC@varric.chelsea.private>

by: Chris Angelico - Tue, 17 Aug 2021 18:19 UTC

On Wed, Aug 18, 2021 at 4:10 AM Barry Scott <barry@barrys-emacs.org> wrote:
>
> def allImports( self, module_name ):
> for line in f:
> words = line.strip().split()
> if words[0:1] == ['import']:
> all_imports.append( words[1] )
>

This will work for a lot of programs, but it depends too much on
coding style. If you feel like trying something a little more
adventurous, I'd recommend looking into the ast module:

>>> import ast
>>> ast.parse("""
.... import foo
.... import bar, baz
.... from quux import spam
.... try: import hello
.... except ImportError: import goodbye
.... """)
<ast.Module object at 0x7f83b65398d0>
>>> m = _
>>> ast.dump(m)
"Module(body=[Import(names=[alias(name='foo')]),
Import(names=[alias(name='bar'), alias(name='baz')]),
ImportFrom(module='quux', names=[alias(name='spam')], level=0),
Try(body=[Import(names=[alias(name='hello')])],
handlers=[ExceptHandler(type=Name(id='ImportError', ctx=Load()),
body=[Import(names=[alias(name='goodbye')])])], orelse=[],
finalbody=[])], type_ignores=[])"

If you ast.parse() the text of a Python script, you'll get a Module
that has all the top-level code in a list. It's then up to you how
much you dig into that. For instance, a simple try/except like this is
fairly common, but if something's inside a FunctionDef, you might want
to ignore it. Or maybe just ignore everything that isn't an Import or
FromImport, which would be a lot easier, but would miss the try/except
example.

The main advantage of ast.parse() is that it no longer cares about
code layout, and it won't be fooled by an import statement inside a
docstring, or anything like that. It's also pretty easy to handle
multiple variants (note how "import bar, baz" just has two things in
the names list).

ChrisA

What is now proved was once only imagin'd. -- William Blake

devel / comp.lang.python / Re: Cyclic imports