imports.py

# -*- coding: utf-8 -*-
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# Copyright (c) 2020 Damien Baty <damien.baty@polyconseil.fr>
# Copyright (c) 2020 Anthony Sottile <asottile@umich.edu>

# Licensed under the GPL: https://www.gnu.org/licenses/old-licenses/gpl-2.0.html
# For details: https://github.com/PyCQA/pylint/blob/master/COPYING

"""imports checkers for Python code"""

import collections
import copy
import os
import sys
from distutils import sysconfig

import astroid
from astroid import modutils
from astroid.decorators import cached

from pylint.checkers import BaseChecker
from pylint.checkers.utils import (
    check_messages,
    is_from_fallback_block,
    node_ignores_exception,
)
from pylint.exceptions import EmptyReportError
from pylint.graph import DotBackend, get_cycles
from pylint.interfaces import IAstroidChecker
from pylint.reporters.ureports.nodes import Paragraph, VerbatimText
from pylint.utils import IsortDriver, get_global_option


def _qualified_names(modname):
    """Split the names of the given module into subparts

    For example,
        _qualified_names('pylint.checkers.ImportsChecker')
    returns
        ['pylint', 'pylint.checkers', 'pylint.checkers.ImportsChecker']
    """
    names = modname.split(".")
    return [".".join(names[0 : i + 1]) for i in range(len(names))]


def _get_import_name(importnode, modname):
    """Get a prepared module name from the given import node

    In the case of relative imports, this will return the
    absolute qualified module name, which might be useful
    for debugging. Otherwise, the initial module name
    is returned unchanged.
    """
    if isinstance(importnode, astroid.ImportFrom):
        if importnode.level:
            root = importnode.root()
            if isinstance(root, astroid.Module):
                modname = root.relative_to_absolute_name(
                    modname, level=importnode.level
                )
    return modname


def _get_first_import(node, context, name, base, level, alias):
    """return the node where [base.]<name> is imported or None if not found
    """
    fullname = "%s.%s" % (base, name) if base else name

    first = None
    found = False
    for first in context.body:
        if first is node:
            continue
        if first.scope() is node.scope() and first.fromlineno > node.fromlineno:
            continue
        if isinstance(first, astroid.Import):
            if any(fullname == iname[0] for iname in first.names):
                found = True
                break
        elif isinstance(first, astroid.ImportFrom):
            if level == first.level:
                for imported_name, imported_alias in first.names:
                    if fullname == "%s.%s" % (first.modname, imported_name):
                        found = True
                        break
                    if (
                        name != "*"
                        and name == imported_name
                        and not (alias or imported_alias)
                    ):
                        found = True
                        break
                if found:
                    break
    if found and not astroid.are_exclusive(first, node):
        return first
    return None


def _ignore_import_failure(node, modname, ignored_modules):
    for submodule in _qualified_names(modname):
        if submodule in ignored_modules:
            return True

    return node_ignores_exception(node, ImportError)


# utilities to represents import dependencies as tree and dot graph ###########


def _make_tree_defs(mod_files_list):
    """get a list of 2-uple (module, list_of_files_which_import_this_module),
    it will return a dictionary to represent this as a tree
    """
    tree_defs = {}
    for mod, files in mod_files_list:
        node = (tree_defs, ())
        for prefix in mod.split("."):
            node = node[0].setdefault(prefix, [{}, []])
        node[1] += files
    return tree_defs


def _repr_tree_defs(data, indent_str=None):
    """return a string which represents imports as a tree"""
    lines = []
    nodes = data.items()
    for i, (mod, (sub, files)) in enumerate(sorted(nodes, key=lambda x: x[0])):
        if not files:
            files = ""
        else:
            files = "(%s)" % ",".join(sorted(files))
        if indent_str is None:
            lines.append("%s %s" % (mod, files))
            sub_indent_str = "  "
        else:
            lines.append(r"%s\-%s %s" % (indent_str, mod, files))
            if i == len(nodes) - 1:
                sub_indent_str = "%s  " % indent_str
            else:
                sub_indent_str = "%s| " % indent_str
        if sub:
            lines.append(_repr_tree_defs(sub, sub_indent_str))
    return "\n".join(lines)


def _dependencies_graph(filename, dep_info):
    """write dependencies as a dot (graphviz) file
    """
    done = {}
    printer = DotBackend(filename[:-4], rankdir="LR")
    printer.emit('URL="." node[shape="box"]')
    for modname, dependencies in sorted(dep_info.items()):
        done[modname] = 1
        printer.emit_node(modname)
        for depmodname in dependencies:
            if depmodname not in done:
                done[depmodname] = 1
                printer.emit_node(depmodname)
    for depmodname, dependencies in sorted(dep_info.items()):
        for modname in dependencies:
            printer.emit_edge(modname, depmodname)
    printer.generate(filename)


def _make_graph(filename, dep_info, sect, gtype):
    """generate a dependencies graph and add some information about it in the
    report's section
    """
    _dependencies_graph(filename, dep_info)
    sect.append(Paragraph("%simports graph has been written to %s" % (gtype, filename)))


# the import checker itself ###################################################

MSGS = {
    "E0401": (
        "Unable to import %s",
        "import-error",
        "Used when pylint has been unable to import a module.",
        {"old_names": [("F0401", "old-import-error")]},
    ),
    "E0402": (
        "Attempted relative import beyond top-level package",
        "relative-beyond-top-level",
        "Used when a relative import tries to access too many levels "
        "in the current package.",
    ),
    "R0401": (
        "Cyclic import (%s)",
        "cyclic-import",
        "Used when a cyclic import between two or more modules is detected.",
    ),
    "W0401": (
        "Wildcard import %s",
        "wildcard-import",
        "Used when `from module import *` is detected.",
    ),
    "W0402": (
        "Uses of a deprecated module %r",
        "deprecated-module",
        "Used a module marked as deprecated is imported.",
    ),
    "W0404": (
        "Reimport %r (imported line %s)",
        "reimported",
        "Used when a module is reimported multiple times.",
    ),
    "W0406": (
        "Module import itself",
        "import-self",
        "Used when a module is importing itself.",
    ),
    "W0407": (
        "Prefer importing %r instead of %r",
        "preferred-module",
        "Used when a module imported has a preferred replacement module.",
    ),
    "W0410": (
        "__future__ import is not the first non docstring statement",
        "misplaced-future",
        "Python 2.5 and greater require __future__ import to be the "
        "first non docstring statement in the module.",
    ),
    "C0410": (
        "Multiple imports on one line (%s)",
        "multiple-imports",
        "Used when import statement importing multiple modules is detected.",
    ),
    "C0411": (
        "%s should be placed before %s",
        "wrong-import-order",
        "Used when PEP8 import order is not respected (standard imports "
        "first, then third-party libraries, then local imports)",
    ),
    "C0412": (
        "Imports from package %s are not grouped",
        "ungrouped-imports",
        "Used when imports are not grouped by packages",
    ),
    "C0413": (
        'Import "%s" should be placed at the top of the module',
        "wrong-import-position",
        "Used when code and imports are mixed",
    ),
    "C0414": (
        "Import alias does not rename original package",
        "useless-import-alias",
        "Used when an import alias is same as original package."
        "e.g using import numpy as numpy instead of import numpy as np",
    ),
    "C0415": (
        "Import outside toplevel (%s)",
        "import-outside-toplevel",
        "Used when an import statement is used anywhere other than the module "
        "toplevel. Move this import to the top of the file.",
    ),
}


DEFAULT_STANDARD_LIBRARY = ()
DEFAULT_KNOWN_THIRD_PARTY = ("enchant",)
DEFAULT_PREFERRED_MODULES = ()


class ImportsChecker(BaseChecker):
    """checks for
    * external modules dependencies
    * relative / wildcard imports
    * cyclic imports
    * uses of deprecated modules
    * uses of modules instead of preferred modules
    """

    __implements__ = IAstroidChecker

    name = "imports"
    msgs = MSGS
    priority = -2
    deprecated_modules = ("optparse", "tkinter.tix")

    options = (
        (
            "deprecated-modules",
            {
                "default": deprecated_modules,
                "type": "csv",
                "metavar": "<modules>",
                "help": "Deprecated modules which should not be used,"
                " separated by a comma.",
            },
        ),
        (
            "preferred-modules",
            {
                "default": DEFAULT_PREFERRED_MODULES,
                "type": "csv",
                "metavar": "<module:preferred-module>",
                "help": "Couples of modules and preferred modules,"
                " separated by a comma.",
            },
        ),
        (
            "import-graph",
            {
                "default": "",
                "type": "string",
                "metavar": "<file.dot>",
                "help": "Create a graph of every (i.e. internal and"
                " external) dependencies in the given file"
                " (report RP0402 must not be disabled).",
            },
        ),
        (
            "ext-import-graph",
            {
                "default": "",
                "type": "string",
                "metavar": "<file.dot>",
                "help": "Create a graph of external dependencies in the"
                " given file (report RP0402 must not be disabled).",
            },
        ),
        (
            "int-import-graph",
            {
                "default": "",
                "type": "string",
                "metavar": "<file.dot>",
                "help": "Create a graph of internal dependencies in the"
                " given file (report RP0402 must not be disabled).",
            },
        ),
        (
            "known-standard-library",
            {
                "default": DEFAULT_STANDARD_LIBRARY,
                "type": "csv",
                "metavar": "<modules>",
                "help": "Force import order to recognize a module as part of "
                "the standard compatibility libraries.",
            },
        ),
        (
            "known-third-party",
            {
                "default": DEFAULT_KNOWN_THIRD_PARTY,
                "type": "csv",
                "metavar": "<modules>",
                "help": "Force import order to recognize a module as part of "
                "a third party library.",
            },
        ),
        (
            "allow-any-import-level",
            {
                "default": (),
                "type": "csv",
                "metavar": "<modules>",
                "help": (
                    "List of modules that can be imported at any level, not just "
                    "the top level one."
                ),
            },
        ),
        (
            "analyse-fallback-blocks",
            {
                "default": False,
                "type": "yn",
                "metavar": "<y_or_n>",
                "help": "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.",
            },
        ),
        (
            "allow-wildcard-with-all",
            {
                "default": False,
                "type": "yn",
                "metavar": "<y_or_n>",
                "help": "Allow wildcard imports from modules that define __all__.",
            },
        ),
    )

    def __init__(self, linter=None):
        BaseChecker.__init__(self, linter)
        self.stats = None
        self.import_graph = None
        self._imports_stack = []
        self._first_non_import_node = None
        self._module_pkg = {}  # mapping of modules to the pkg they belong in
        self._allow_any_import_level = set()
        self.reports = (
            ("RP0401", "External dependencies", self._report_external_dependencies),
            ("RP0402", "Modules dependencies graph", self._report_dependencies_graph),
        )

        self._site_packages = self._compute_site_packages()

    @staticmethod
    def _compute_site_packages():
        def _normalized_path(path):
            return os.path.normcase(os.path.abspath(path))

        paths = set()
        real_prefix = getattr(sys, "real_prefix", None)
        for prefix in filter(None, (real_prefix, sys.prefix)):
            path = sysconfig.get_python_lib(prefix=prefix)
            path = _normalized_path(path)
            paths.add(path)

        # Handle Debian's derivatives /usr/local.
        if os.path.isfile("/etc/debian_version"):
            for prefix in filter(None, (real_prefix, sys.prefix)):
                libpython = os.path.join(
                    prefix,
                    "local",
                    "lib",
                    "python" + sysconfig.get_python_version(),
                    "dist-packages",
                )
                paths.add(libpython)
        return paths

    def open(self):
        """called before visiting project (i.e set of modules)"""
        self.linter.add_stats(dependencies={})
        self.linter.add_stats(cycles=[])
        self.stats = self.linter.stats
        self.import_graph = collections.defaultdict(set)
        self._module_pkg = {}  # mapping of modules to the pkg they belong in
        self._excluded_edges = collections.defaultdict(set)
        self._ignored_modules = get_global_option(self, "ignored-modules", default=[])
        # Build a mapping {'module': 'preferred-module'}
        self.preferred_modules = dict(
            module.split(":")
            for module in self.config.preferred_modules
            if ":" in module
        )
        self._allow_any_import_level = set(self.config.allow_any_import_level)

    def _import_graph_without_ignored_edges(self):
        filtered_graph = copy.deepcopy(self.import_graph)
        for node in filtered_graph:
            filtered_graph[node].difference_update(self._excluded_edges[node])
        return filtered_graph

    def close(self):
        """called before visiting project (i.e set of modules)"""
        if self.linter.is_message_enabled("cyclic-import"):
            graph = self._import_graph_without_ignored_edges()
            vertices = list(graph)
            for cycle in get_cycles(graph, vertices=vertices):
                self.add_message("cyclic-import", args=" -> ".join(cycle))

    @check_messages(*MSGS)
    def visit_import(self, node):
        """triggered when an import statement is seen"""
        self._check_reimport(node)
        self._check_import_as_rename(node)
        self._check_toplevel(node)

        names = [name for name, _ in node.names]
        if len(names) >= 2:
            self.add_message("multiple-imports", args=", ".join(names), node=node)

        for name in names:
            self._check_deprecated_module(node, name)
            self._check_preferred_module(node, name)
            imported_module = self._get_imported_module(node, name)
            if isinstance(node.parent, astroid.Module):
                # Allow imports nested
                self._check_position(node)
            if isinstance(node.scope(), astroid.Module):
                self._record_import(node, imported_module)

            if imported_module is None:
                continue

            self._add_imported_module(node, imported_module.name)

    @check_messages(*MSGS)
    def visit_importfrom(self, node):
        """triggered when a from statement is seen"""
        basename = node.modname
        imported_module = self._get_imported_module(node, basename)

        self._check_import_as_rename(node)
        self._check_misplaced_future(node)
        self._check_deprecated_module(node, basename)
        self._check_preferred_module(node, basename)
        self._check_wildcard_imports(node, imported_module)
        self._check_same_line_imports(node)
        self._check_reimport(node, basename=basename, level=node.level)
        self._check_toplevel(node)

        if isinstance(node.parent, astroid.Module):
            # Allow imports nested
            self._check_position(node)
        if isinstance(node.scope(), astroid.Module):
            self._record_import(node, imported_module)
        if imported_module is None:
            return
        for name, _ in node.names:
            if name != "*":
                self._add_imported_module(node, "%s.%s" % (imported_module.name, name))
            else:
                self._add_imported_module(node, imported_module.name)

    @check_messages(*MSGS)
    def leave_module(self, node):
        # Check imports are grouped by category (standard, 3rd party, local)
        std_imports, ext_imports, loc_imports = self._check_imports_order(node)

        # Check that imports are grouped by package within a given category
        met_import = set()  #  set for 'import x' style
        met_from = set()  #  set for 'from x import y' style
        current_package = None
        for import_node, import_name in std_imports + ext_imports + loc_imports:
            if not self.linter.is_message_enabled(
                "ungrouped-imports", import_node.fromlineno
            ):
                continue
            if isinstance(import_node, astroid.node_classes.ImportFrom):
                met = met_from
            else:
                met = met_import
            package, _, _ = import_name.partition(".")
            if current_package and current_package != package and package in met:
                self.add_message("ungrouped-imports", node=import_node, args=package)
            current_package = package
            met.add(package)

        self._imports_stack = []
        self._first_non_import_node = None

    def compute_first_non_import_node(self, node):
        if not self.linter.is_message_enabled("wrong-import-position", node.fromlineno):
            return
        # if the node does not contain an import instruction, and if it is the
        # first node of the module, keep a track of it (all the import positions
        # of the module will be compared to the position of this first
        # instruction)
        if self._first_non_import_node:
            return
        if not isinstance(node.parent, astroid.Module):
            return
        nested_allowed = [astroid.TryExcept, astroid.TryFinally]
        is_nested_allowed = [
            allowed for allowed in nested_allowed if isinstance(node, allowed)
        ]
        if is_nested_allowed and any(
            node.nodes_of_class((astroid.Import, astroid.ImportFrom))
        ):
            return
        if isinstance(node, astroid.Assign):
            # Add compatibility for module level dunder names
            # https://www.python.org/dev/peps/pep-0008/#module-level-dunder-names
            valid_targets = [
                isinstance(target, astroid.AssignName)
                and target.name.startswith("__")
                and target.name.endswith("__")
                for target in node.targets
            ]
            if all(valid_targets):
                return
        self._first_non_import_node = node

    visit_tryfinally = (
        visit_tryexcept
    ) = (
        visit_assignattr
    ) = (
        visit_assign
    ) = (
        visit_ifexp
    ) = visit_comprehension = visit_expr = visit_if = compute_first_non_import_node

    def visit_functiondef(self, node):
        if not self.linter.is_message_enabled("wrong-import-position", node.fromlineno):
            return
        # If it is the first non import instruction of the module, record it.
        if self._first_non_import_node:
            return

        # Check if the node belongs to an `If` or a `Try` block. If they
        # contain imports, skip recording this node.
        if not isinstance(node.parent.scope(), astroid.Module):
            return

        root = node
        while not isinstance(root.parent, astroid.Module):
            root = root.parent

        if isinstance(root, (astroid.If, astroid.TryFinally, astroid.TryExcept)):
            if any(root.nodes_of_class((astroid.Import, astroid.ImportFrom))):
                return

        self._first_non_import_node = node

    visit_classdef = visit_for = visit_while = visit_functiondef

    def _check_misplaced_future(self, node):
        basename = node.modname
        if basename == "__future__":
            # check if this is the first non-docstring statement in the module
            prev = node.previous_sibling()
            if prev:
                # consecutive future statements are possible
                if not (
                    isinstance(prev, astroid.ImportFrom)
                    and prev.modname == "__future__"
                ):
                    self.add_message("misplaced-future", node=node)
            return

    def _check_same_line_imports(self, node):
        # Detect duplicate imports on the same line.
        names = (name for name, _ in node.names)
        counter = collections.Counter(names)
        for name, count in counter.items():
            if count > 1:
                self.add_message("reimported", node=node, args=(name, node.fromlineno))

    def _check_position(self, node):
        """Check `node` import or importfrom node position is correct

        Send a message  if `node` comes before another instruction
        """
        # if a first non-import instruction has already been encountered,
        # it means the import comes after it and therefore is not well placed
        if self._first_non_import_node:
            self.add_message("wrong-import-position", node=node, args=node.as_string())

    def _record_import(self, node, importedmodnode):
        """Record the package `node` imports from"""
        if isinstance(node, astroid.ImportFrom):
            importedname = node.modname
        else:
            importedname = importedmodnode.name if importedmodnode else None
        if not importedname:
            importedname = node.names[0][0].split(".")[0]

        if isinstance(node, astroid.ImportFrom) and (node.level or 0) >= 1:
            # We need the importedname with first point to detect local package
            # Example of node:
            #  'from .my_package1 import MyClass1'
            #  the output should be '.my_package1' instead of 'my_package1'
            # Example of node:
            #  'from . import my_package2'
            #  the output should be '.my_package2' instead of '{pyfile}'
            importedname = "." + importedname

        self._imports_stack.append((node, importedname))

    @staticmethod
    def _is_fallback_import(node, imports):
        imports = [import_node for (import_node, _) in imports]
        return any(astroid.are_exclusive(import_node, node) for import_node in imports)

    def _check_imports_order(self, _module_node):
        """Checks imports of module `node` are grouped by category

        Imports must follow this order: standard, 3rd party, local
        """
        std_imports = []
        third_party_imports = []
        first_party_imports = []
        # need of a list that holds third or first party ordered import
        external_imports = []
        local_imports = []
        third_party_not_ignored = []
        first_party_not_ignored = []
        local_not_ignored = []
        isort_driver = IsortDriver(self.config)
        for node, modname in self._imports_stack:
            if modname.startswith("."):
                package = "." + modname.split(".")[1]
            else:
                package = modname.split(".")[0]
            nested = not isinstance(node.parent, astroid.Module)
            ignore_for_import_order = not self.linter.is_message_enabled(
                "wrong-import-order", node.fromlineno
            )
            import_category = isort_driver.place_module(package)
            node_and_package_import = (node, package)
            if import_category in ("FUTURE", "STDLIB"):
                std_imports.append(node_and_package_import)
                wrong_import = (
                    third_party_not_ignored
                    or first_party_not_ignored
                    or local_not_ignored
                )
                if self._is_fallback_import(node, wrong_import):
                    continue
                if wrong_import and not nested:
                    self.add_message(
                        "wrong-import-order",
                        node=node,
                        args=(
                            'standard import "%s"' % node.as_string(),
                            '"%s"' % wrong_import[0][0].as_string(),
                        ),
                    )
            elif import_category == "THIRDPARTY":
                third_party_imports.append(node_and_package_import)
                external_imports.append(node_and_package_import)
                if not nested and not ignore_for_import_order:
                    third_party_not_ignored.append(node_and_package_import)
                wrong_import = first_party_not_ignored or local_not_ignored
                if wrong_import and not nested:
                    self.add_message(
                        "wrong-import-order",
                        node=node,
                        args=(
                            'third party import "%s"' % node.as_string(),
                            '"%s"' % wrong_import[0][0].as_string(),
                        ),
                    )
            elif import_category == "FIRSTPARTY":
                first_party_imports.append(node_and_package_import)
                external_imports.append(node_and_package_import)
                if not nested and not ignore_for_import_order:
                    first_party_not_ignored.append(node_and_package_import)
                wrong_import = local_not_ignored
                if wrong_import and not nested:
                    self.add_message(
                        "wrong-import-order",
                        node=node,
                        args=(
                            'first party import "%s"' % node.as_string(),
                            '"%s"' % wrong_import[0][0].as_string(),
                        ),
                    )
            elif import_category == "LOCALFOLDER":
                local_imports.append((node, package))
                if not nested and not ignore_for_import_order:
                    local_not_ignored.append((node, package))
        return std_imports, external_imports, local_imports

    def _get_imported_module(self, importnode, modname):
        try:
            return importnode.do_import_module(modname)
        except astroid.TooManyLevelsError:
            if _ignore_import_failure(importnode, modname, self._ignored_modules):
                return None
            self.add_message("relative-beyond-top-level", node=importnode)
        except astroid.AstroidSyntaxError as exc:
            message = "Cannot import {!r} due to syntax error {!r}".format(
                modname, str(exc.error)  # pylint: disable=no-member; false positive
            )
            self.add_message("syntax-error", line=importnode.lineno, args=message)

        except astroid.AstroidBuildingException:
            if not self.linter.is_message_enabled("import-error"):
                return None
            if _ignore_import_failure(importnode, modname, self._ignored_modules):
                return None
            if not self.config.analyse_fallback_blocks and is_from_fallback_block(
                importnode
            ):
                return None

            dotted_modname = _get_import_name(importnode, modname)
            self.add_message("import-error", args=repr(dotted_modname), node=importnode)

    def _add_imported_module(self, node, importedmodname):
        """notify an imported module, used to analyze dependencies"""
        module_file = node.root().file
        context_name = node.root().name
        base = os.path.splitext(os.path.basename(module_file))[0]

        try:
            importedmodname = modutils.get_module_part(importedmodname, module_file)
        except ImportError:
            pass

        if context_name == importedmodname:
            self.add_message("import-self", node=node)

        elif not modutils.is_standard_module(importedmodname):
            # if this is not a package __init__ module
            if base != "__init__" and context_name not in self._module_pkg:
                # record the module's parent, or the module itself if this is
                # a top level module, as the package it belongs to
                self._module_pkg[context_name] = context_name.rsplit(".", 1)[0]

            # handle dependencies
            importedmodnames = self.stats["dependencies"].setdefault(
                importedmodname, set()
            )
            if context_name not in importedmodnames:
                importedmodnames.add(context_name)

            # update import graph
            self.import_graph[context_name].add(importedmodname)
            if not self.linter.is_message_enabled("cyclic-import", line=node.lineno):
                self._excluded_edges[context_name].add(importedmodname)

    def _check_deprecated_module(self, node, mod_path):
        """check if the module is deprecated"""
        for mod_name in self.config.deprecated_modules:
            if mod_path == mod_name or mod_path.startswith(mod_name + "."):
                self.add_message("deprecated-module", node=node, args=mod_path)

    def _check_preferred_module(self, node, mod_path):
        """check if the module has a preferred replacement"""
        if mod_path in self.preferred_modules:
            self.add_message(
                "preferred-module",
                node=node,
                args=(self.preferred_modules[mod_path], mod_path),
            )

    def _check_import_as_rename(self, node):
        names = node.names
        for name in names:
            if not all(name):
                return

            real_name = name[0]
            splitted_packages = real_name.rsplit(".")
            real_name = splitted_packages[-1]
            imported_name = name[1]
            # consider only following cases
            # import x as x
            # and ignore following
            # import x.y.z as z
            if real_name == imported_name and len(splitted_packages) == 1:
                self.add_message("useless-import-alias", node=node)

    def _check_reimport(self, node, basename=None, level=None):
        """check if the import is necessary (i.e. not already done)"""
        if not self.linter.is_message_enabled("reimported"):
            return

        frame = node.frame()
        root = node.root()
        contexts = [(frame, level)]
        if root is not frame:
            contexts.append((root, None))

        for known_context, known_level in contexts:
            for name, alias in node.names:
                first = _get_first_import(
                    node, known_context, name, basename, known_level, alias
                )
                if first is not None:
                    self.add_message(
                        "reimported", node=node, args=(name, first.fromlineno)
                    )

    def _report_external_dependencies(self, sect, _, _dummy):
        """return a verbatim layout for displaying dependencies"""
        dep_info = _make_tree_defs(self._external_dependencies_info().items())
        if not dep_info:
            raise EmptyReportError()
        tree_str = _repr_tree_defs(dep_info)
        sect.append(VerbatimText(tree_str))

    def _report_dependencies_graph(self, sect, _, _dummy):
        """write dependencies as a dot (graphviz) file"""
        dep_info = self.stats["dependencies"]
        if not dep_info or not (
            self.config.import_graph
            or self.config.ext_import_graph
            or self.config.int_import_graph
        ):
            raise EmptyReportError()
        filename = self.config.import_graph
        if filename:
            _make_graph(filename, dep_info, sect, "")
        filename = self.config.ext_import_graph
        if filename:
            _make_graph(filename, self._external_dependencies_info(), sect, "external ")
        filename = self.config.int_import_graph
        if filename:
            _make_graph(filename, self._internal_dependencies_info(), sect, "internal ")

    def _filter_dependencies_graph(self, internal):
        """build the internal or the external dependency graph"""
        graph = collections.defaultdict(set)
        for importee, importers in self.stats["dependencies"].items():
            for importer in importers:
                package = self._module_pkg.get(importer, importer)
                is_inside = importee.startswith(package)
                if is_inside and internal or not is_inside and not internal:
                    graph[importee].add(importer)
        return graph

    @cached
    def _external_dependencies_info(self):
        """return cached external dependencies information or build and
        cache them
        """
        return self._filter_dependencies_graph(internal=False)

    @cached
    def _internal_dependencies_info(self):
        """return cached internal dependencies information or build and
        cache them
        """
        return self._filter_dependencies_graph(internal=True)

    def _check_wildcard_imports(self, node, imported_module):
        if node.root().package:
            # Skip the check if in __init__.py issue #2026
            return

        wildcard_import_is_allowed = self._wildcard_import_is_allowed(imported_module)
        for name, _ in node.names:
            if name == "*" and not wildcard_import_is_allowed:
                self.add_message("wildcard-import", args=node.modname, node=node)

    def _wildcard_import_is_allowed(self, imported_module):
        return (
            self.config.allow_wildcard_with_all
            and imported_module is not None
            and "__all__" in imported_module.locals
        )

    def _check_toplevel(self, node):
        """Check whether the import is made outside the module toplevel.
        """
        # If the scope of the import is a module, then obviously it is
        # not outside the module toplevel.
        if isinstance(node.scope(), astroid.Module):
            return

        module_names = [
            "{}.{}".format(node.modname, name[0])
            if isinstance(node, astroid.ImportFrom)
            else name[0]
            for name in node.names
        ]

        # Get the full names of all the imports that are not whitelisted.
        scoped_imports = [
            name for name in module_names if name not in self._allow_any_import_level
        ]

        if scoped_imports:
            self.add_message(
                "import-outside-toplevel", args=", ".join(scoped_imports), node=node
            )


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