gh-135676: lexical analysis: Improve section on Numeric literals#134850
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Doc/reference/lexical_analysis.rst Outdated
| Instead, :ref:`complex numbers <typesnumeric>` can be written | ||
| as adding the complex number's real part and imaginary part. | ||
| .. productionlist:: python-grammar | ||
| imagnumber: (`floatnumber` | `digitpart`) ("j" | "J") | ||
| For example, the imaginary number 3.1+4\ *i* can be written as adding the | ||
| real number 3.1 to the imaginary number 4\ *i*. |
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Sorry, but this is a wrong picture.
The CPython has no pure-imaginary numbers and above decomposition is invalid in general. Simple counterexample:
>>> -0.0+0j 0j >>> complex(-0.0, 0) (-0+0j)Previous description was valid: "An imaginary literal yields a complex number with a real part of 0.0."
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The key point is this is lexical analysis. Python indeed has no imaginary literals, but the tokeniser does -- 4+16j is three tokens.
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I think L1093 should say 'the complex number ...', though.
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Sure, but 16j is not an imaginary number. It's a complex number with a real part +0.0. And complex number in the Python currently can't be "written as adding the complex number's real part and imaginary part."
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16j is not an imaginary number; but 16i is :)
I agree that this could be clearer. Will update. (Not sure when, as I recently volunteered to focus on f-strings first.)
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16j is not an imaginary number; but 16i is :)
But you are talking not about mathematics, but Python's complex numbers.
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I've reworded the intro for Imaginary literals. Is this clearer?
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This pr mix
- change productlist directive to grammar-snippet, that solves referenced issue
- substantial rewrite of sections about literals.
I don't see which issue solves 2). But, maybe it's better to do in a separate pr?
encukou commented Jun 12, 2025
This PR is about the rewrite; changing the directives is a minor part of that. Perhaps I could use more granular issues -- have one for adding the |
encukou changed the title encukou commented Jun 18, 2025
I've opened #135676 for rewording Lexical analysis, and attached this PR to that. |
encukou commented Jun 18, 2025
Merging; please note any follow-ups on the issue :) |
encukou merged commit 21f3d15 into python:mainUh oh!
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Thanks @encukou for the PR 🌮🎉.. I'm working now to backport this PR to: 3.14. |
pythonGH-134850) (cherry picked from commit 21f3d15) Co-authored-by: Petr Viktorin <encukou@gmail.com>
GH-135677 is a backport of this pull request to the 3.14 branch. |
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5 participants
Each section is expanded, and now progresses from simple cases and examples to more involved ones, ending with the formal grammar.
This uses meta-syntax that I want to add to the introduction in #134443. I'm marking it as draft until that's merged.
📚 Documentation preview 📚: https://cpython-previews--134850.org.readthedocs.build/