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Pylint

About​

  • Pylint is a static code analyser for Python 2 or 3. The latest version supports Python 3.8.0 and above.
  • Pylint analyses your code without actually running it. It checks for errors, enforces a coding standard, looks for code smells, and can make suggestions about how the code could be refactored.

Installation​

  • You can install pylint in your project's venv using command pip install pylint or pip3 install pylint

Config file for .pylintrc​

  • Create and use a file named .pylintrc in your python project root folder
  • You can use the .pylintrc file contents given below
  • The .pylintrc content given below is taken from https://google.github.io/styleguide/pylintrc, with few modifications
# Tekdi specific changes made in google's .pylintrc
# # Added in [MESSAGES CONTROL] 
# # # disable = line-too-long

# This Pylint rcfile contains a best-effort configuration to uphold the
# best-practices and style described in the Google Python style guide:
#   https://google.github.io/styleguide/pyguide.html
#
# Its canonical open-source location is:
#   https://google.github.io/styleguide/pylintrc

[MAIN]

# Files or directories to be skipped. They should be base names, not paths.
ignore=third_party

# Files or directories matching the regex patterns are skipped. The regex
# matches against base names, not paths.
ignore-patterns=

# Pickle collected data for later comparisons.
persistent=no

# List of plugins (as comma separated values of python modules names) to load,
# usually to register additional checkers.
load-plugins=

# Use multiple processes to speed up Pylint.
jobs=4

# Allow loading of arbitrary C extensions. Extensions are imported into the
# active Python interpreter and may run arbitrary code.
unsafe-load-any-extension=no


[MESSAGES CONTROL]

# Only show warnings with the listed confidence levels. Leave empty to show
# all. Valid levels: HIGH, INFERENCE, INFERENCE_FAILURE, UNDEFINED
confidence=

# Enable the message, report, category or checker with the given id(s). You can
# either give multiple identifier separated by comma (,) or put this option
# multiple time (only on the command line, not in the configuration file where
# it should appear only once). See also the "--disable" option for examples.
#enable=

# Disable the message, report, category or checker with the given id(s). You
# can either give multiple identifiers separated by comma (,) or put this
# option multiple times (only on the command line, not in the configuration
# file where it should appear only once).You can also use "--disable=all" to
# disable everything first and then reenable specific checks. For example, if
# you want to run only the similarities checker, you can use "--disable=all
# --enable=similarities". If you want to run only the classes checker, but have
# no Warning level messages displayed, use"--disable=all --enable=classes
# --disable=W"
disable=R,
        abstract-method,
        apply-builtin,
        arguments-differ,
        attribute-defined-outside-init,
        backtick,
        bad-option-value,
        basestring-builtin,
        buffer-builtin,
        c-extension-no-member,
        consider-using-enumerate,
        cmp-builtin,
        cmp-method,
        coerce-builtin,
        coerce-method,
        delslice-method,
        div-method,
        eq-without-hash,
        execfile-builtin,
        file-builtin,
        filter-builtin-not-iterating,
        fixme,
        getslice-method,
        global-statement,
        hex-method,
        idiv-method,
        implicit-str-concat,
        import-error,
        import-self,
        import-star-module-level,
        input-builtin,
        intern-builtin,
        invalid-str-codec,
        locally-disabled,
        long-builtin,
        long-suffix,
        map-builtin-not-iterating,
        misplaced-comparison-constant,
        missing-function-docstring,
        metaclass-assignment,
        next-method-called,
        next-method-defined,
        no-absolute-import,
        no-init,  # added
        no-member,
        no-name-in-module,
        no-self-use,
        nonzero-method,
        oct-method,
        old-division,
        old-ne-operator,
        old-octal-literal,
        old-raise-syntax,
        parameter-unpacking,
        print-statement,
        raising-string,
        range-builtin-not-iterating,
        raw_input-builtin,
        rdiv-method,
        reduce-builtin,
        relative-import,
        reload-builtin,
        round-builtin,
        setslice-method,
        signature-differs,
        standarderror-builtin,
        suppressed-message,
        sys-max-int,
        trailing-newlines,
        unichr-builtin,
        unicode-builtin,
        unnecessary-pass,
        unpacking-in-except,
        useless-else-on-loop,
        useless-suppression,
        using-cmp-argument,
        wrong-import-order,
        xrange-builtin,
        zip-builtin-not-iterating,
        line-too-long,


[REPORTS]

# Set the output format. Available formats are text, parseable, colorized, msvs
# (visual studio) and html. You can also give a reporter class, eg
# mypackage.mymodule.MyReporterClass.
output-format=text

# Tells whether to display a full report or only the messages
reports=no

# Python expression which should return a note less than 10 (10 is the highest
# note). You have access to the variables errors warning, statement which
# respectively contain the number of errors / warnings messages and the total
# number of statements analyzed. This is used by the global evaluation report
# (RP0004).
evaluation=10.0 - ((float(5 * error + warning + refactor + convention) / statement) * 10)

# Template used to display messages. This is a python new-style format string
# used to format the message information. See doc for all details
#msg-template=


[BASIC]

# Good variable names which should always be accepted, separated by a comma
good-names=main,_

# Bad variable names which should always be refused, separated by a comma
bad-names=

# Colon-delimited sets of names that determine each other's naming style when
# the name regexes allow several styles.
name-group=

# Include a hint for the correct naming format with invalid-name
include-naming-hint=no

# List of decorators that produce properties, such as abc.abstractproperty. Add
# to this list to register other decorators that produce valid properties.
property-classes=abc.abstractproperty,cached_property.cached_property,cached_property.threaded_cached_property,cached_property.cached_property_with_ttl,cached_property.threaded_cached_property_with_ttl

# Regular expression matching correct function names
function-rgx=^(?:(?P<exempt>setUp|tearDown|setUpModule|tearDownModule)|(?P<camel_case>_?[A-Z][a-zA-Z0-9]*)|(?P<snake_case>_?[a-z][a-z0-9_]*))$

# Regular expression matching correct variable names
variable-rgx=^[a-z][a-z0-9_]*$

# Regular expression matching correct constant names
const-rgx=^(_?[A-Z][A-Z0-9_]*|__[a-z0-9_]+__|_?[a-z][a-z0-9_]*)$

# Regular expression matching correct attribute names
attr-rgx=^_{0,2}[a-z][a-z0-9_]*$

# Regular expression matching correct argument names
argument-rgx=^[a-z][a-z0-9_]*$

# Regular expression matching correct class attribute names
class-attribute-rgx=^(_?[A-Z][A-Z0-9_]*|__[a-z0-9_]+__|_?[a-z][a-z0-9_]*)$

# Regular expression matching correct inline iteration names
inlinevar-rgx=^[a-z][a-z0-9_]*$

# Regular expression matching correct class names
class-rgx=^_?[A-Z][a-zA-Z0-9]*$

# Regular expression matching correct module names
module-rgx=^(_?[a-z][a-z0-9_]*|__init__)$

# Regular expression matching correct method names
method-rgx=(?x)^(?:(?P<exempt>_[a-z0-9_]+__|runTest|setUp|tearDown|setUpTestCase|tearDownTestCase|setupSelf|tearDownClass|setUpClass|(test|assert)_*[A-Z0-9][a-zA-Z0-9_]*|next)|(?P<camel_case>_{0,2}[A-Z][a-zA-Z0-9_]*)|(?P<snake_case>_{0,2}[a-z][a-z0-9_]*))$

# Regular expression which should only match function or class names that do
# not require a docstring.
no-docstring-rgx=(__.*__|main|test.*|.*test|.*Test)$

# Minimum line length for functions/classes that require docstrings, shorter
# ones are exempt.
docstring-min-length=12


[TYPECHECK]

# List of decorators that produce context managers, such as
# contextlib.contextmanager. Add to this list to register other decorators that
# produce valid context managers.
contextmanager-decorators=contextlib.contextmanager,contextlib2.contextmanager

# List of module names for which member attributes should not be checked
# (useful for modules/projects where namespaces are manipulated during runtime
# and thus existing member attributes cannot be deduced by static analysis. It
# supports qualified module names, as well as Unix pattern matching.
ignored-modules=

# List of class names for which member attributes should not be checked (useful
# for classes with dynamically set attributes). This supports the use of
# qualified names.
ignored-classes=optparse.Values,thread._local,_thread._local

# List of members which are set dynamically and missed by pylint inference
# system, and so shouldn't trigger E1101 when accessed. Python regular
# expressions are accepted.
generated-members=


[FORMAT]

# Maximum number of characters on a single line.
max-line-length=80

# TODO(https://github.com/pylint-dev/pylint/issues/3352): Direct pylint to exempt
# lines made too long by directives to pytype.

# Regexp for a line that is allowed to be longer than the limit.
ignore-long-lines=(?x)(
  ^\s*(\#\ )?<?https?://\S+>?$|
  ^\s*(from\s+\S+\s+)?import\s+.+$)

# Allow the body of an if to be on the same line as the test if there is no
# else.
single-line-if-stmt=yes

# Maximum number of lines in a module
max-module-lines=99999

# String used as indentation unit.  The internal Google style guide mandates 2
# spaces.  Google's externaly-published style guide says 4, consistent with
# PEP 8.  Here, we use 2 spaces, for conformity with many open-sourced Google
# projects (like TensorFlow).
indent-string='    '

# Number of spaces of indent required inside a hanging  or continued line.
indent-after-paren=4

# Expected format of line ending, e.g. empty (any line ending), LF or CRLF.
expected-line-ending-format=


[MISCELLANEOUS]

# List of note tags to take in consideration, separated by a comma.
notes=TODO


[STRING]

# This flag controls whether inconsistent-quotes generates a warning when the
# character used as a quote delimiter is used inconsistently within a module.
check-quote-consistency=yes


[VARIABLES]

# Tells whether we should check for unused import in __init__ files.
init-import=no

# A regular expression matching the name of dummy variables (i.e. expectedly
# not used).
dummy-variables-rgx=^\*{0,2}(_$|unused_|dummy_)

# List of additional names supposed to be defined in builtins. Remember that
# you should avoid to define new builtins when possible.
additional-builtins=

# List of strings which can identify a callback function by name. A callback
# name must start or end with one of those strings.
callbacks=cb_,_cb

# List of qualified module names which can have objects that can redefine
# builtins.
redefining-builtins-modules=six,six.moves,past.builtins,future.builtins,functools


[LOGGING]

# Logging modules to check that the string format arguments are in logging
# function parameter format
logging-modules=logging,absl.logging,tensorflow.io.logging


[SIMILARITIES]

# Minimum lines number of a similarity.
min-similarity-lines=4

# Ignore comments when computing similarities.
ignore-comments=yes

# Ignore docstrings when computing similarities.
ignore-docstrings=yes

# Ignore imports when computing similarities.
ignore-imports=no


[SPELLING]

# Spelling dictionary name. Available dictionaries: none. To make it working
# install python-enchant package.
spelling-dict=

# List of comma separated words that should not be checked.
spelling-ignore-words=

# A path to a file that contains private dictionary; one word per line.
spelling-private-dict-file=

# Tells whether to store unknown words to indicated private dictionary in
# --spelling-private-dict-file option instead of raising a message.
spelling-store-unknown-words=no


[IMPORTS]

# Deprecated modules which should not be used, separated by a comma
deprecated-modules=regsub,
                   TERMIOS,
                   Bastion,
                   rexec,
                   sets

# Create a graph of every (i.e. internal and external) dependencies in the
# given file (report RP0402 must not be disabled)
import-graph=

# Create a graph of external dependencies in the given file (report RP0402 must
# not be disabled)
ext-import-graph=

# Create a graph of internal dependencies in the given file (report RP0402 must
# not be disabled)
int-import-graph=

# Force import order to recognize a module as part of the standard
# compatibility libraries.
known-standard-library=

# Force import order to recognize a module as part of a third party library.
known-third-party=enchant, absl

# Analyse import fallback blocks. This can be used to support both Python 2 and
# 3 compatible code, which means that the block might have code that exists
# only in one or another interpreter, leading to false positives when analysed.
analyse-fallback-blocks=no


[CLASSES]

# List of method names used to declare (i.e. assign) instance attributes.
defining-attr-methods=__init__,
                      __new__,
                      setUp

# List of member names, which should be excluded from the protected access
# warning.
exclude-protected=_asdict,
                  _fields,
                  _replace,
                  _source,
                  _make

# List of valid names for the first argument in a class method.
valid-classmethod-first-arg=cls,
                            class_

# List of valid names for the first argument in a metaclass class method.
valid-metaclass-classmethod-first-arg=mcs

How to use Pylint?​

A) Using pylint outside the editor, via terminal​

  • Goto your project repo cd my-python-project
  • Activate your project's venv source /path-to-your-projects-env/bin/activate
  • Run pylint as

Example of scanning all .py files from current directory

pylint *.py

Example of scanning all files from current directory (.) recursively, ignoring .venv folder

pylint --recursive=y --ignore=.venv .

B) Using pylint inside VSCode editor​

1) Install this VSCode extension for Pylint​

2) VSCode Settings for pylint​

You can edit settings.json of VSCode as below

  • To run pylint on code change
  • To always show notifications
{
    "pylint.lintOnChange": true,
    "pylint.showNotifications": "always",
}

3) Open any python file in editor​

  • Open Problems tab in console, to see linting errors if any

4) References​