lint: Speed up and fix flake8 checks #30723

I am not sure how I feel about this --preview flag

According to their github docs in the configuration section

To opt in to the latest lint rules, formatter style changes, interface updates, and more, enable preview mode by setting preview = true in your configuration file or passing --preview on the command line. Preview mode enables a collection of unstable features that may change prior to stabilization

Yes, I am aware. However, the dependency is fully pinned, so if a feature changes, it will be noticed. This is no different from any of the other dependencies being pinned to avoid silently breaking updates.

However, it isn't needed, so I've removed it to restore the previous flags.

In commit: lint: Remove python lint rules that are SyntaxError

Nit: I believe all of F701-F707 result in SyntaxError and should be removed

<details>

<summary> The following examples resulted in SyntaxError's for Python 2.7.18 </summary>

f701.py:

def func(x):
    if x > 5:
        break

for i in range(10):
    func(i)        # <--- call function

f702.py:

def func(x):
    if x > 5:
        continue

for i in range(10):
    func(i)

f704.py:

step = 1

for x in range(0, 10, step):
  for y in range(0, 10, step):
    yield (x,y)

f706.py:

step = 1

for x in range(0, 10, step):
  for y in range(0, 10, step):
    return (x,y)

f707.py:

try:
    x = 1 / 0
except ZeroDivisionError:
    print("Divided by zero")
except:
    print("Generic exception")
except ValueError:
    print("Value error")

</details>

Thx, done

In commit: lint: Remove python whitespace and shadowing lint rules This check doesn't seem like a terrible idea, but not supported by ruff.

I fail to see how it could possibly catch a bug, or how this has caught a bug (or ever hit at all) over the last years.

Apart from this, shadowing is allowed in all languages/contexts used by this project.

It seems inconsistent, or mostly a style-taste either way.

In commit: lint: Remove python whitespace and shadowing lint rules This seems reasonable to me, but not available without the --preview argument

As explained in the commit message, the Python language has a strong built-in whitespace requirement already. Obviously, one can define more indentation requirements, but this seems arbitrary at best, without a clear benefit of catching real bugs.

Obviously, anyone is free and encouraged to use a Python formatter of their choice locally. This is unchanged by this pull request.

I agree, this and the above definitely won't catch bugs, some projects like to use extensive and arbitrary lint checks for style rules to prevent bikeshedding and PR's over non-critical style choices, but I don't think that's an issue in Bitcoin Core's python code, so I think you're right.

In commit: lint: Remove python whitespace and shadowing lint rules

+1 on dropping checks that result in IndentError

some of the other checks removed here seem reasonable to me e.g. E125, and E275, but not available/hidden behind preview flag in ruff so I'm ~0 on whether or not to remove the rest of them

Same reply here: #30723 (review)

nit: this should've been removed in the earlier commit that dropped syntaxerror checks

Thx, done

nit:

# F622: two or more starred expressions in an assignment (a, *b, *c = d)
a, *b, *c = [1, 2, 3, 4]

results in a syntaxerror in Python 2.7.18

Thx, done

nit:

# E902: TokenError: EOF in multi-line string
"""
Unterminated string literal

results in a syntaxerror in Python 2.7.18

Thx, done

nit: ruff accepts the checks as comma separated values to --select=

    let checks = format!(
        "--select={}",
        [
            "B006", // mutable-argument-default
            "B008", // function-call-in-default-argument
            "E101", // indentation contains mixed spaces and tabs
            "E401", // multiple imports on one line
            "E402", // module level import not at top of file
            "E701", // multiple statements on one line (colon)
            "E702", // multiple statements on one line (semicolon)
            "E703", // statement ends with a semicolon
            "E711", // comparison to None should be 'if cond is None:'
            "E714", // test for object identity should be "is not"
            "E721", // do not compare types, use "isinstance()"
            "E722", // do not use bare 'except'
            "E742", // do not define classes named "l", "O", or "I"
            "E743", // do not define functions named "l", "O", or "I"
            "E902", // TokenError: EOF in multi-line string
            "F401", // module imported but unused
            "F402", // import module from line N shadowed by loop variable
            "F403", // 'from foo_module import *' used; unable to detect undefined names
            "F404", // future import(s) name after other statements
            "F405", // foo_function may be undefined, or defined from star imports: bar_module
            "F406", // "from module import *" only allowed at module level
            "F407", // an undefined __future__ feature name was imported
            "F601", // dictionary key name repeated with different values
            "F602", // dictionary key variable name repeated with different values
            "F621", // too many expressions in an assignment with star-unpacking
            "F622", // two or more starred expressions in an assignment (a, *b, *c = d)
            "F631", // assertion test is a tuple, which are always True
            "F632", // use ==/!= to compare str, bytes, and int literals
            "F701", // a break statement outside of a while or for loop
            "F702", // a continue statement outside of a while or for loop
            "F704", // a yield or yield from statement outside of a function
            "F706", // a return statement outside of a function/method
            "F707", // an except: block as not the last exception handler
            "F811", // redefinition of unused name from line N
            "F821", // undefined name 'Foo'
            "F822", // undefined name name in __all__
            "F823", // local variable name … referenced before assignment
            "F841", // local variable 'foo' is assigned to but never used
            "W191", // indentation contains tabs
            "W291", // trailing whitespace
            "W292", // no newline at end of file
            "W293", // blank line contains whitespace
            "W605", // invalid escape sequence "x"
        ]
        .join(",")
    );

Thx, done