The import statement

import_stmt     ::=  "import" module ["as" name] ( "," module ["as" name] )*
                     | "from" relative_module "import" identifier ["as" name]
                     ( "," identifier ["as" name] )*
                     | "from" relative_module "import" "(" identifier ["as" name]
                     ( "," identifier ["as" name] )* [","] ")"
                     | "from" module "import" "*"
module          ::=  (identifier ".")* identifier
relative_module ::=  "."* module | "."+
name            ::=  identifier

The basic import statement (no from clause) is executed in two steps:

  1. find a module, loading and initializing it if necessary
  2. define a name or names in the local namespace for the scope where the import statement occurs.

When the statement contains multiple clauses (separated by commas) the two steps are carried out separately for each clause, just as though the clauses had been separated out into individiual import statements.

The details of the first step, finding and loading modules are described in greater detail in the section on the import system, which also describes the various types of packages and modules that can be imported, as well as all the hooks that can be used to customize the import system. Note that failures in this step may indicate either that the module could not be located, or that an error occurred while initializing the module, which includes execution of the module’s code.

If the requested module is retrieved successfully, it will be made available in the local namespace in one of three ways:

The from form uses a slightly more complex process:

  1. find the module specified in the from clause, loading and initializing it if necessary;
  2. for each of the identifiers specified in the import clauses:
    1. check if the imported module has an attribute by that name
    2. if not, attempt to import a submodule with that name and then check the imported module again for that attribute
    3. if the attribute is not found, ImportError is raised.
    4. otherwise, a reference to that value is stored in the local namespace, using the name in the as clause if it is present, otherwise using the attribute name

Examples:

import foo                 # foo imported and bound locally
import foo.bar.baz         # foo.bar.baz imported, foo bound locally
import foo.bar.baz as fbb  # foo.bar.baz imported and bound as fbb
from foo.bar import baz    # foo.bar.baz imported and bound as baz
from foo import attr       # foo imported and foo.attr bound as attr

If the list of identifiers is replaced by a star ('*'), all public names defined in the module are bound in the local namespace for the scope where the import statement occurs.

The public names defined by a module are determined by checking the module’s namespace for a variable named __all__; if defined, it must be a sequence of strings which are names defined or imported by that module. The names given in __all__ are all considered public and are required to exist. If __all__ is not defined, the set of public names includes all names found in the module’s namespace which do not begin with an underscore character ('_'). __all__ should contain the entire public API. It is intended to avoid accidentally exporting items that are not part of the API (such as library modules which were imported and used within the module).

The wild card form of import — from module import * — is only allowed at the module level. Attempting to use it in class or function definitions will raise a SyntaxError.

When specifying what module to import you do not have to specify the absolute name of the module. When a module or package is contained within another package it is possible to make a relative import within the same top package without having to mention the package name. By using leading dots in the specified module or package after from you can specify how high to traverse up the current package hierarchy without specifying exact names. One leading dot means the current package where the module making the import exists. Two dots means up one package level. Three dots is up two levels, etc. So if you execute from . import mod from a module in the pkg package then you will end up importing pkg.mod. If you execute from ..subpkg2 import mod from within pkg.subpkg1 you will import pkg.subpkg2.mod. The specification for relative imports is contained within PEP 328.

importlib.import_module() is provided to support applications that determine dynamically the modules to be loaded.