path: root/pylint/checkers/design_analysis.py

# Copyright (c) 2003-2013 LOGILAB S.A. (Paris, FRANCE).
# http://www.logilab.fr/ -- mailto:contact@logilab.fr
#
# This program is free software; you can redistribute it and/or modify it under
# the terms of the GNU General Public License as published by the Free Software
# Foundation; either version 2 of the License, or (at your option) any later
# version.
#
# This program is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
# FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License along with
# this program; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
"""check for signs of poor design"""

import re
from collections import defaultdict

from astroid import If, BoolOp

from pylint.interfaces import IAstroidChecker
from pylint.checkers import BaseChecker
from pylint.checkers.utils import check_messages

# regexp for ignored argument name
IGNORED_ARGUMENT_NAMES = re.compile('_.*')


MSGS = {
    'R0901': ('Too many ancestors (%s/%s)',
              'too-many-ancestors',
              'Used when class has too many parent classes, try to reduce \
              this to get a simpler (and so easier to use) class.'),
    'R0902': ('Too many instance attributes (%s/%s)',
              'too-many-instance-attributes',
              'Used when class has too many instance attributes, try to reduce \
              this to get a simpler (and so easier to use) class.'),
    'R0903': ('Too few public methods (%s/%s)',
              'too-few-public-methods',
              'Used when class has too few public methods, so be sure it\'s \
              really worth it.'),
    'R0904': ('Too many public methods (%s/%s)',
              'too-many-public-methods',
              'Used when class has too many public methods, try to reduce \
              this to get a simpler (and so easier to use) class.'),

    'R0911': ('Too many return statements (%s/%s)',
              'too-many-return-statements',
              'Used when a function or method has too many return statement, \
              making it hard to follow.'),
    'R0912': ('Too many branches (%s/%s)',
              'too-many-branches',
              'Used when a function or method has too many branches, \
              making it hard to follow.'),
    'R0913': ('Too many arguments (%s/%s)',
              'too-many-arguments',
              'Used when a function or method takes too many arguments.'),
    'R0914': ('Too many local variables (%s/%s)',
              'too-many-locals',
              'Used when a function or method has too many local variables.'),
    'R0915': ('Too many statements (%s/%s)',
              'too-many-statements',
              'Used when a function or method has too many statements. You \
              should then split it in smaller functions / methods.'),
    'R0916': ('Too many boolean expressions in if statement (%s/%s)',
              'too-many-boolean-expressions',
              'Used when a if statement contains too many boolean '
              'expressions'),
    }


def _count_boolean_expressions(bool_op):
    """Counts the number of boolean expressions in BoolOp `bool_op` (recursive)

    example: a and (b or c or (d and e)) ==> 5 boolean expressions
    """
    nb_bool_expr = 0
    for bool_expr in bool_op.get_children():
        if isinstance(bool_expr, BoolOp):
            nb_bool_expr += _count_boolean_expressions(bool_expr)
        else:
            nb_bool_expr += 1
    return nb_bool_expr


class MisdesignChecker(BaseChecker):
    """checks for sign of poor/misdesign:
    * number of methods, attributes, local variables...
    * size, complexity of functions, methods
    """

    __implements__ = (IAstroidChecker,)

    # configuration section name
    name = 'design'
    # messages
    msgs = MSGS
    priority = -2
    # configuration options
    options = (('max-args',
                {'default' : 5, 'type' : 'int', 'metavar' : '<int>',
                 'help': 'Maximum number of arguments for function / method'}
               ),
               ('ignored-argument-names',
                {'default' : IGNORED_ARGUMENT_NAMES,
                 'type' :'regexp', 'metavar' : '<regexp>',
                 'help' : 'Argument names that match this expression will be '
                          'ignored. Default to name with leading underscore'}
               ),
               ('max-locals',
                {'default' : 15, 'type' : 'int', 'metavar' : '<int>',
                 'help': 'Maximum number of locals for function / method body'}
               ),
               ('max-returns',
                {'default' : 6, 'type' : 'int', 'metavar' : '<int>',
                 'help': 'Maximum number of return / yield for function / '
                         'method body'}
               ),
               ('max-branches',
                {'default' : 12, 'type' : 'int', 'metavar' : '<int>',
                 'help': 'Maximum number of branch for function / method body'}
               ),
               ('max-statements',
                {'default' : 50, 'type' : 'int', 'metavar' : '<int>',
                 'help': 'Maximum number of statements in function / method '
                         'body'}
               ),
               ('max-parents',
                {'default' : 7,
                 'type' : 'int',
                 'metavar' : '<num>',
                 'help' : 'Maximum number of parents for a class (see R0901).'}
               ),
               ('max-attributes',
                {'default' : 7,
                 'type' : 'int',
                 'metavar' : '<num>',
                 'help' : 'Maximum number of attributes for a class \
(see R0902).'}
               ),
               ('min-public-methods',
                {'default' : 2,
                 'type' : 'int',
                 'metavar' : '<num>',
                 'help' : 'Minimum number of public methods for a class \
(see R0903).'}
               ),
               ('max-public-methods',
                {'default' : 20,
                 'type' : 'int',
                 'metavar' : '<num>',
                 'help' : 'Maximum number of public methods for a class \
(see R0904).'}
               ),
               ('max-bool-expr',
                {'default': 5,
                 'type': 'int',
                 'metavar': '<num>',
                 'help': 'Maximum number of boolean expressions in a if '
                         'statement'}
               ),
              )

    def __init__(self, linter=None):
        BaseChecker.__init__(self, linter)
        self.stats = None
        self._returns = None
        self._branches = None
        self._stmts = 0

    def open(self):
        """initialize visit variables"""
        self.stats = self.linter.add_stats()
        self._returns = []
        self._branches = defaultdict(int)

    @check_messages('too-many-ancestors', 'too-many-instance-attributes',
                    'too-few-public-methods', 'too-many-public-methods')
    def visit_classdef(self, node):
        """check size of inheritance hierarchy and number of instance attributes
        """
        # Is the total inheritance hierarchy is 7 or less?
        nb_parents = len(list(node.ancestors()))
        if nb_parents > self.config.max_parents:
            self.add_message('too-many-ancestors', node=node,
                             args=(nb_parents, self.config.max_parents))
        # Does the class contain less than 20 attributes for
        # non-GUI classes (40 for GUI)?
        # FIXME detect gui classes
        if len(node.instance_attrs) > self.config.max_attributes:
            self.add_message('too-many-instance-attributes', node=node,
                             args=(len(node.instance_attrs),
                                   self.config.max_attributes))

    @check_messages('too-few-public-methods', 'too-many-public-methods')
    def leave_classdef(self, node):
        """check number of public methods"""
        my_methods = sum(1 for method in node.mymethods()
                         if not method.name.startswith('_'))
        all_methods = sum(1 for method in node.methods()
                          if not method.name.startswith('_'))

        # Does the class contain less than n public methods ?
        # This checks only the methods defined in the current class,
        # since the user might not have control over the classes
        # from the ancestors. It avoids some false positives
        # for classes such as unittest.TestCase, which provides
        # a lot of assert methods. It doesn't make sense to warn
        # when the user subclasses TestCase to add his own tests.
        if my_methods > self.config.max_public_methods:
            self.add_message('too-many-public-methods', node=node,
                             args=(my_methods,
                                   self.config.max_public_methods))
        # stop here for exception, metaclass and interface classes
        if node.type != 'class':
            return

        # Does the class contain more than n public methods ?
        # This checks all the methods defined by ancestors and
        # by the current class.
        if all_methods < self.config.min_public_methods:
            self.add_message('too-few-public-methods', node=node,
                             args=(all_methods,
                                   self.config.min_public_methods))

    @check_messages('too-many-return-statements', 'too-many-branches',
                    'too-many-arguments', 'too-many-locals',
                    'too-many-statements')
    def visit_functiondef(self, node):
        """check function name, docstring, arguments, redefinition,
        variable names, max locals
        """
        # init branch and returns counters
        self._returns.append(0)
        # check number of arguments
        args = node.args.args
        if args is not None:
            ignored_args_num = len(
                [arg for arg in args
                 if self.config.ignored_argument_names.match(arg.name)])
            argnum = len(args) - ignored_args_num
            if  argnum > self.config.max_args:
                self.add_message('too-many-arguments', node=node,
                                 args=(len(args), self.config.max_args))
        else:
            ignored_args_num = 0
        # check number of local variables
        locnum = len(node.locals) - ignored_args_num
        if locnum > self.config.max_locals:
            self.add_message('too-many-locals', node=node,
                             args=(locnum, self.config.max_locals))
        # init statements counter
        self._stmts = 1

    @check_messages('too-many-return-statements', 'too-many-branches',
                    'too-many-arguments', 'too-many-locals',
                    'too-many-statements')
    def leave_functiondef(self, node):
        """most of the work is done here on close:
        checks for max returns, branch, return in __init__
        """
        returns = self._returns.pop()
        if returns > self.config.max_returns:
            self.add_message('too-many-return-statements', node=node,
                             args=(returns, self.config.max_returns))
        branches = self._branches[node]
        if branches > self.config.max_branches:
            self.add_message('too-many-branches', node=node,
                             args=(branches, self.config.max_branches))
        # check number of statements
        if self._stmts > self.config.max_statements:
            self.add_message('too-many-statements', node=node,
                             args=(self._stmts, self.config.max_statements))

    def visit_return(self, _):
        """count number of returns"""
        if not self._returns:
            return # return outside function, reported by the base checker
        self._returns[-1] += 1

    def visit_default(self, node):
        """default visit method -> increments the statements counter if
        necessary
        """
        if node.is_statement:
            self._stmts += 1

    def visit_tryexcept(self, node):
        """increments the branches counter"""
        branches = len(node.handlers)
        if node.orelse:
            branches += 1
        self._inc_branch(node, branches)
        self._stmts += branches

    def visit_tryfinally(self, node):
        """increments the branches counter"""
        self._inc_branch(node, 2)
        self._stmts += 2

    @check_messages('too-many-boolean-expressions')
    def visit_if(self, node):
        """increments the branches counter and checks boolean expressions"""
        self._check_boolean_expressions(node)
        branches = 1
        # don't double count If nodes coming from some 'elif'
        if node.orelse and (len(node.orelse) > 1 or
                            not isinstance(node.orelse[0], If)):
            branches += 1
        self._inc_branch(node, branches)
        self._stmts += branches

    def _check_boolean_expressions(self, node):
        """Go through "if" node `node` and counts its boolean expressions

        if the "if" node test is a BoolOp node
        """
        condition = node.test
        if not isinstance(condition, BoolOp):
            return
        nb_bool_expr = _count_boolean_expressions(condition)
        if nb_bool_expr > self.config.max_bool_expr:
            self.add_message('too-many-boolean-expressions', node=condition,
                             args=(nb_bool_expr, self.config.max_bool_expr))

    def visit_while(self, node):
        """increments the branches counter"""
        branches = 1
        if node.orelse:
            branches += 1
        self._inc_branch(node, branches)

    visit_for = visit_while

    def _inc_branch(self, node, branchesnum=1):
        """increments the branches counter"""
        self._branches[node.scope()] += branchesnum


def register(linter):
    """required method to auto register this checker """
    linter.register_checker(MisdesignChecker(linter))