[perflint] Implement try-except-in-loop (PERF203)

crates/ruff/resources/test/fixtures/perflint/PERF203.py

@@ -0,0 +1,28 @@
+for i in range(10):
+    try:  # PERF203
+        print(f"{i}")
+    except:
+        print("error")
+
+try:
+    for i in range(10):
+        print(f"{i}")
+except:
+    print("error")
+
+i = 0
+while i < 10:  # PERF203
+    try:
+        print(f"{i}")
+    except:
+        print("error")
+
+    i += 1
+
+try:
+    i = 0
+    while i < 10:
+        print(f"{i}")
+        i += 1
+except:
+    print("error")

crates/ruff/src/checkers/ast/mod.rs

@@ -1430,6 +1430,9 @@ where
                 if self.enabled(Rule::UselessElseOnLoop) {
                     pylint::rules::useless_else_on_loop(self, stmt, body, orelse);
                 }
+                if self.enabled(Rule::TryExceptInLoop) {
+                    perflint::rules::try_except_in_loop(self, body);
+                }
             }
             Stmt::For(ast::StmtFor {
                 target,
@@ -1477,6 +1480,9 @@ where
                     if self.enabled(Rule::InDictKeys) {
                         flake8_simplify::rules::key_in_dict_for(self, target, iter);
                     }
+                    if self.enabled(Rule::TryExceptInLoop) {
+                        perflint::rules::try_except_in_loop(self, body);
+                    }
                 }
                 if self.enabled(Rule::IncorrectDictIterator) {
                     perflint::rules::incorrect_dict_iterator(self, target, iter);

crates/ruff/src/codes.rs

@@ -786,6 +786,7 @@ pub fn code_to_rule(linter: Linter, code: &str) -> Option<(RuleGroup, Rule)> {
         // perflint
         (Perflint, "101") => (RuleGroup::Unspecified, rules::perflint::rules::UnnecessaryListCast),
         (Perflint, "102") => (RuleGroup::Unspecified, rules::perflint::rules::IncorrectDictIterator),
+        (Perflint, "203") => (RuleGroup::Unspecified, rules::perflint::rules::TryExceptInLoop),
 
         // flake8-fixme
         (Flake8Fixme, "001") => (RuleGroup::Unspecified, rules::flake8_fixme::rules::LineContainsFixme),

crates/ruff/src/rules/perflint/mod.rs

@@ -15,6 +15,7 @@ mod tests {
 
     #[test_case(Rule::UnnecessaryListCast, Path::new("PERF101.py"))]
     #[test_case(Rule::IncorrectDictIterator, Path::new("PERF102.py"))]
+    #[test_case(Rule::TryExceptInLoop, Path::new("PERF203.py"))]
     fn rules(rule_code: Rule, path: &Path) -> Result<()> {
         let snapshot = format!("{}_{}", rule_code.noqa_code(), path.to_string_lossy());
         let diagnostics = test_path(

crates/ruff/src/rules/perflint/rules/mod.rs

@@ -1,5 +1,7 @@
 pub(crate) use incorrect_dict_iterator::*;
+pub(crate) use try_except_in_loop::*;
 pub(crate) use unnecessary_list_cast::*;
 
 mod incorrect_dict_iterator;
+mod try_except_in_loop;
 mod unnecessary_list_cast;

crates/ruff/src/rules/perflint/rules/try_except_in_loop.rs

@@ -0,0 +1,74 @@
+use rustpython_parser::ast::{self, Ranged, Stmt};
+
+use ruff_diagnostics::{Diagnostic, Violation};
+use ruff_macros::{derive_message_formats, violation};
+
+use crate::checkers::ast::Checker;
+use crate::settings::types::PythonVersion;
+
+/// ## What it does
+/// Checks for uses of except handling via `try`-`except` within `for` and
+/// `while` loops.
+///
+/// ## Why is this bad?
+/// Exception handling via `try`-`except` blocks incurs some performance
+/// overhead, regardless of whether an exception is raised.
+///
+/// When possible, refactor your code to put the entire loop into the
+/// `try`-`except` block, rather than wrapping each iteration in a separate
+/// `try`-`except` block.
+///
+/// This rule is only enforced for Python versions prior to 3.11, which
+/// introduced "zero cost" exception handling.
+///
+/// Note that, as with all `perflint` rules, this is only intended as a
+/// micro-optimization, and will have a negligible impact on performance in
+/// most cases.
+///
+/// ## Example
+/// ```python
+/// for i in range(10):
+///     try:
+///         print(i * i)
+///     except:
+///         break
+/// ```
+///
+/// Use instead:
+/// ```python
+/// try:
+///     for i in range(10):
+///         print(i * i)
+/// except:
+///     break
+/// ```
+///
+/// ## Options
+/// - `target-version`
+#[violation]
+pub struct TryExceptInLoop;
+
+impl Violation for TryExceptInLoop {
+    #[derive_message_formats]
+    fn message(&self) -> String {
+        format!("`try`-`except` within a loop incurs performance overhead")
+    }
+}
+
+/// PERF203
+pub(crate) fn try_except_in_loop(checker: &mut Checker, body: &[Stmt]) {
+    if checker.settings.target_version >= PythonVersion::Py311 {
+        return;
+    }
+
+    checker.diagnostics.extend(body.iter().filter_map(|stmt| {
+        if let Stmt::Try(ast::StmtTry { handlers, .. }) = stmt {
+            handlers
+                .iter()
+                .next()
+                .map(|handler| Diagnostic::new(TryExceptInLoop, handler.range()))
+        } else {
+            None
+        }
+    }));
+}

crates/ruff/src/rules/perflint/snapshots/ruff__rules__perflint__tests__PERF203_PERF203.py.snap

@@ -0,0 +1,28 @@
+---
+source: crates/ruff/src/rules/perflint/mod.rs
+---
+PERF203.py:4:5: PERF203 `try`-`except` within a loop incurs performance overhead
+  |
+2 |       try:  # PERF203
+3 |           print(f"{i}")
+4 |       except:
+  |  _____^
+5 | |         print("error")
+  | |______________________^ PERF203
+6 |   
+7 |   try:
+  |
+
+PERF203.py:17:5: PERF203 `try`-`except` within a loop incurs performance overhead
+   |
+15 |       try:
+16 |           print(f"{i}")
+17 |       except:
+   |  _____^
+18 | |         print("error")
+   | |______________________^ PERF203
+19 |   
+20 |       i += 1
+   |
+
+

scripts/pyproject.toml

@@ -18,6 +18,7 @@ ignore = [
   "G",     # flake8-logging
   "T",     # flake8-print
   "FBT",   # flake8-boolean-trap
+  "PERF",  # perflint
 ]
 
 [tool.ruff.isort]