"SyntaxError: no binding for nonlocal 'X' found" when X is a parameter

[David Caro]

Observed behavior

When Jedi finds a function parameter declared as nonlocal inside an inner function, the "nonlocal" it's marked wrongly as a syntax error.

This code snippet reproduce the issue:

def function_with_nonlocal_param(param=None):
    def inner():
        nonlocal param  # Jedi: SyntaxError: no binding for nonlocal 'param' found
        if param is None:
            param = "None (string)"
        print(f"Param (inner): {param}")

    inner()
    print(f"Param (outer): {param}")


def function_with_nonlocal_value(param=None):
    value = param

    def inner():
        nonlocal value  # No Jedi error here
        if value is None:
            value = "None (string)"
        print(f"Value (inner): {value}")

    inner()
    print(f"Value (outer): {value}")


if __name__ == '__main__':
    function_with_nonlocal_param(10)
    function_with_nonlocal_param()
    function_with_nonlocal_value(10)
    function_with_nonlocal_value()

The output with Python 3.7 or greater shows that both nonlocal directive uses are legal and works as expected:

$ python jedi-nonlocal-poc.py
Param (inner): 10
Param (outer): 10
Param (inner): None (string)
Param (outer): None (string)
Value (inner): 10
Value (outer): 10
Value (inner): None (string)
Value (outer): None (string)

Expected behavior

Jedi should handle correctly the legal "nonlocal" uses and don't mark it as errors.

Additional notes

I'm using:

• Python 3.9.1
• Neovim 0.4.4
• coc-jedi 0.18.1
• jedi-language-server 0.23.1

Here's the pip freeze output from the jedi-language-server virtualenv:

click==7.1.2
jedi==0.18.0
jedi-language-server==0.23.1
parso==0.8.1
pygls==0.9.1

[Samuel Roeca]

Interesting... I've just tried with the latest version of jedi-language-server / coc-jedi and I can't reproduce (I'm on Python 3.8, neovim 0.5.0-dev).

Which Python version are you using with your editor? Maybe Jedi is installed / observing a virtual environment or system installation of Python that precedes 3.7 while you're editing?

[David Caro]

In my work maybe but I've reproduced the bug in my computer, which only have Python 3.9, so no it's not because it's seeing a Python version without nonlocal support, or partial support, or anything like that.
I even checked out the coc-jedi venv Python version, it's 3.9.1:

$ pwd
/home/terseus/.config/coc/extensions/node_modules/coc-jedi
$ which python
/home/terseus/.config/coc/extensions/node_modules/coc-jedi/.venv/bin/python
$ python --version
Python 3.9.1

However I cloned the jedi repo and wrote the following static analysis test and the bug doesn't reproduce, so doesn't look jedi's fault:

def nonlocal_variable():
    def inner():
        nonlocal value
        value = 10

    value = 20


def nonlocal_parameter(param):
    def inner():
        nonlocal param
        param = 10

Now, I've just tried it again while writing this and noticed that with this code, the error doesn't happen in my editor either:

def nonlocal_parameter(param):
    def inner():
        nonlocal param
        param = 10

    param = 20    # Thanks to this line the error is gone!

I suspect that jedi-language-server it's not recognizing the param parameter to be available in the inner context but it does when it's a variable explicitly declared in the outer context, I'll try to reproduce the bug directly with jedi-language-server and get you back.

[David Caro]

@pappasam I've added the pip freeze output from the coc-jedi virtualenv, just in case.

[Samuel Roeca]

@Terseus thanks for the detail, hopefully we can get to the bottom of this soon!

I've done my best to replicate the important parts of your environment:

Python: 3.9.1
Jedi: 0.18.1

Once set up, I've written and run a small script that (on my end) appears to prove that this is a jedi issue (not to say it's not important to me, just that there's little I can do to fix it within jedi-language-server itself).

Please copy/paste the following code into a source file, make sure you're running Python 3.9.1 with jedi 0.18.1 installed, and run it.

import jedi

code = """
def nonlocal_variable():
    def inner():
        nonlocal value
        value = 10

    value = 20


def nonlocal_parameter(param):
    def inner():
        nonlocal param
        param = 10
"""

script = jedi.Script(code=code)

errors = script.get_syntax_errors()
print(errors)
print(errors[0].get_message())

The following lines should print to the console:

[<SyntaxError from=(12, 17) to=(12, 22)>]
SyntaxError: no binding for nonlocal 'param' found

This, to me, demonstrates that jedi is returning the syntax error message without any help (or hindrance) from jedi-language-server.

Please let me know if this is what you observe. If not, we may be running into an operating system issue... I'm on Ubuntu 20.0.4.

[David Caro]

@pappasam Yep you're right, definitely it's a Jedi bug.

Sorry, I clearly made a mistake thinking a static analysis test (like these) should have exposed the error and didn't know enough of the Jedi API to write a simpler test like yours.

I've opened an issue in Jedi with this problem: https://github.com/davidhalter/jedi/issues/1753

Thanks for your help ^_^