Pylint Bug: Bad-name-rgxs Mangles Regex With Commas
Hey everyone, let's dive into a tricky bug that's been messing with Pylint, specifically how it handles regular expressions in the bad-name-rgxs option. This issue can cause Pylint to crash unexpectedly when your regular expressions contain commas. So, if you've run into this, you're not alone! Let's break down what's happening and how to work around it.
Bug Description
The core of the problem lies in how Pylint parses the bad-name-rgxs option. Instead of treating the entire string as a single regular expression, it splits the string at each comma. This wouldn't be an issue if your regex didn't contain commas, but when it does, Pylint misinterprets the parts after the comma as separate regex patterns. This often leads to parsing errors, as these split segments are typically incomplete or invalid regex expressions on their own. The user's configuration clearly demonstrates this issue, leading to an immediate crash of Pylint.
Let's emphasize this: the bad-name-rgxs option is intended to allow you to specify regular expressions that define what constitutes a "bad" name in your code. This is super useful for enforcing coding standards and catching naming inconsistencies. However, because of this bug, any regex containing a comma will cause problems. This greatly limits the flexibility and power of this feature. It's crucial for Pylint to correctly handle commas within regular expressions to allow users to define complex and accurate naming conventions.
When you encounter this bug, you'll find that Pylint becomes unable to function correctly with the intended regular expressions. This not only hinders your ability to enforce proper naming conventions but also disrupts your workflow by causing unexpected crashes. The impact is significant, especially in large projects where consistent naming is paramount. Imagine trying to enforce a complex naming scheme across hundreds of files only to be thwarted by this parsing issue—frustrating, right? We need a robust solution that allows Pylint to interpret regular expressions containing commas correctly so that you can use this powerful feature without fear of crashes.
Configuration Example
Here’s a peek at the configuration that triggers this bug. Notice the regular expression includes a comma within the pattern:
[tool.pylint.basic]
# capture group ensures that the part after the comma is an invalid regular
# expression, causing pylint to crash
bad-name-rgxs = "(foo{1,3})"
In this example, the intention is to define a regular expression (foo{1,3}) which should match strings like "foo", "fooo", but not "fooooo". However, because Pylint splits on the comma, it tries to compile foo{1 and 3}) as separate regular expressions. The second part, 3}), is obviously an invalid regex, leading to the crash. This scenario perfectly illustrates the problem: commas within a regular expression string are incorrectly treated as delimiters, breaking the intended functionality.
This configuration specifically causes a crash because the portion of the string after the comma results in an invalid regular expression. Pylint attempts to compile this invalid expression, which then throws an error and halts the process. The use of a capture group in the intended regex is not the issue itself; rather, it's the comma within the string that's the culprit. To fix this, we need Pylint to either ignore commas within the string or provide a way to escape them, ensuring that the entire string is treated as a single, complete regular expression. The current behavior makes it impossible to use certain valid regular expressions, severely limiting the utility of the bad-name-rgxs option.
Command Used
The command to reproduce this issue is straightforward:
pylint foo.py
This simple command highlights how easily the bug can be triggered. Running Pylint on virtually any Python file (foo.py in this case) with the problematic configuration will lead to the crash. This simplicity underscores the critical nature of the bug; it's not something that requires a complex setup or specific code patterns to manifest. Any project using the bad-name-rgxs option with commas in the regular expressions is at risk. This makes it essential to find a solution or workaround to prevent these crashes and ensure Pylint can be used effectively.
The fact that such a basic command triggers the issue also emphasizes the need for robust testing of Pylint's configuration parsing. It suggests that the parsing logic for the bad-name-rgxs option may not have been thoroughly tested with regular expressions containing commas. Comprehensive testing with a wide range of regular expressions, including those with special characters and delimiters, is crucial to prevent similar issues in the future. The ease with which this bug can be reproduced makes it a prime candidate for inclusion in Pylint's regression test suite, ensuring that any future changes do not reintroduce this problem.
Pylint Output
The traceback you'll see is quite verbose, but the key part is the re.error: missing ), unterminated subpattern at position 0 message. This tells us that Python’s regular expression engine (re) is choking on the mangled input:
Traceback (most recent call last):
File "/home/lihu/.venv/bin/pylint", line 8, in <module>
sys.exit(run_pylint())
File "/home/lihu/.venv/lib/python3.10/site-packages/pylint/__init__.py", line 25, in run_pylint
PylintRun(argv or sys.argv[1:])
File "/home/lihu/.venv/lib/python3.10/site-packages/pylint/lint/run.py", line 161, in __init__
args = _config_initialization(
File "/home/lihu/.venv/lib/python3.10/site-packages/pylint/config/config_initialization.py", line 57, in _config_initialization
linter._parse_configuration_file(config_args)
File "/home/lihu/.venv/lib/python3.10/site-packages/pylint/config/arguments_manager.py", line 244, in _parse_configuration_file
self.config, parsed_args = self._arg_parser.parse_known_args(
File "/usr/lib/python3.10/argparse.py", line 1870, in parse_known_args
namespace, args = self._parse_known_args(args, namespace)
File "/usr/lib/python3.10/argparse.py", line 2079, in _parse_known_args
start_index = consume_optional(start_index)
File "/usr/lib/python3.10/argparse.py", line 2019, in consume_optional
take_action(action, args, option_string)
File "/usr/lib/python3.10/argparse.py", line 1931, in take_action
argument_values = self._get_values(action, argument_strings)
File "/usr/lib/python3.10/argparse.py", line 2462, in _get_values
value = self._get_value(action, arg_string)
File "/usr/lib/python3.10/argparse.py", line 2495, in _get_value
result = type_func(arg_string)
File "/home/lihu/.venv/lib/python3.10/site-packages/pylint/config/argument.py", line 106, in _regexp_csv_transfomer
patterns.append(re.compile(pattern))
File "/usr/lib/python3.10/re.py", line 251, in compile
return _compile(pattern, flags)
File "/usr/lib/python3.10/re.py", line 303, in _compile
p = sre_compile.compile(pattern, flags)
File "/usr/lib/python3.10/sre_compile.py", line 764, in compile
p = sre_parse.parse(p, flags)
File "/usr/lib/python3.10/sre_parse.py", line 950, in parse
p = _parse_sub(source, state, flags & SRE_FLAG_VERBOSE, 0)
File "/usr/lib/python3.10/sre_parse.py", line 443, in _parse_sub
itemsappend(_parse(source, state, verbose, nested + 1,
File "/usr/lib/python3.10/sre_parse.py", line 838, in _parse
raise source.error("missing ), unterminated subpattern",
re.error: missing ), unterminated subpattern at position 0
This traceback is a clear indicator that Pylint's configuration parsing is the root cause. The re.error confirms that Python's regex engine is receiving an invalid pattern due to the incorrect splitting of the string at the comma. The specific error, "missing ), unterminated subpattern," pinpoints the issue: Pylint is attempting to compile a regex fragment that lacks a closing parenthesis, a direct result of the comma-based splitting. This is not an issue with the regular expression syntax itself, but rather with how Pylint interprets the configuration string.
Understanding the traceback is crucial for debugging. It highlights the flow of execution, starting from the pylint command and drilling down into the configuration parsing logic. The key lines are those involving argparse.py and pylint/config/argument.py, which show how Pylint processes the configuration file and applies transformations. The _regexp_csv_transfomer function is particularly relevant, as it's responsible for handling comma-separated values, which is where the problem arises. By tracing the error back to this function, we can see that the intended list of regex patterns is being mishandled, leading to the compilation error.
Expected Behavior
Ideally, Pylint should allow any valid regular expression to be used within the bad-name-rgxs option. If direct support isn't possible due to the comma issue, a mechanism to escape commas (e.g., using a backslash) would provide a workable solution. This would give users the flexibility to define complex regular expressions without causing Pylint to crash. The ability to use commas within regex patterns is essential for defining certain types of naming conventions, such as those involving multiple alternatives or specific character sequences.
Consider this: regular expressions are a powerful tool for pattern matching, and the bad-name-rgxs option is meant to leverage this power for enforcing coding standards. The current limitation severely restricts the kinds of rules you can define. For instance, you might want to create a regex that checks for variable names containing specific prefixes or suffixes, or that adhere to a certain case style. If your regex needs to include a comma to accurately capture these patterns, you're out of luck. This hinders the ability to create fine-grained naming rules, ultimately diminishing the value of the bad-name-rgxs feature.
Providing a way to escape commas would not only fix the crashing issue but also greatly enhance the usability of the bad-name-rgxs option. It would allow users to define more complex and accurate regular expressions, leading to better enforcement of coding standards and fewer false positives. The goal is to make the configuration process as intuitive and flexible as possible, allowing developers to focus on writing code rather than wrestling with configuration quirks. A simple escape mechanism, like a backslash, would be a straightforward and effective way to achieve this.
Pylint Version and Environment
This bug was observed in:
pylint 2.14.4
astroid 2.11.7
Python 3.10.4 (main, Apr 2 2022, 09:04:19) [GCC 11.2.0]
It’s important to note the specific versions of Pylint, Astroid, and Python, as this helps in isolating the bug and determining its scope. Knowing the exact versions allows developers to reproduce the issue in a controlled environment and verify that any fixes are effective. In this case, the bug was observed in Pylint 2.14.4 with Astroid 2.11.7, running on Python 3.10.4. If you're using these versions or later, you're likely to encounter this issue if you use commas in your bad-name-rgxs regular expressions.
The environment also plays a role in bug reproducibility. Here, the OS is Pop! OS 22.04. While this bug is unlikely to be OS-specific (as it's related to Python and Pylint's parsing logic), providing the OS information helps in understanding the context in which the bug was encountered. If the bug were to be OS-specific, this information would be crucial in identifying the underlying cause. However, in this case, the issue is more likely tied to Pylint's internal workings and how it handles regular expressions with commas.
OS / Environment
The operating system used was Pop! OS 22.04.
Additional Dependencies
No additional dependencies were reported.
In conclusion, this bad-name-rgxs bug in Pylint is a real head-scratcher, especially if you rely on regular expressions with commas. Hopefully, this breakdown helps you understand the issue and maybe even find a workaround until a proper fix is released. Keep an eye on Pylint's updates, and let's hope for a resolution soon! This highlights the need for careful parsing of configuration options, especially when dealing with complex data types like regular expressions. Stay tuned for more updates and potential solutions!