About
import functionality in Python
In order to use the names (generally, variable and function definitions) defined in a module, you must either:
- import the module itself
- or import the specific definitions,
you want to use from the module.
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Configuration
By default, no import is allowed. You need to add a Python Package - init .py to the directory package
Syntax
No import
if you don't import the module, you must refer to a procedure or variable defined therein by using its qualified name.
The module
import myModuleName
myModuleName.func()
A name (function, variable,…)
- Importing only a function of the module. Import statement that imports names from a module directly into the importing module’s symbol table.
from module import func1, func2
# Example
from math import sqrt
print sqrt(25) # The full qualified name is here not needed
From source
import imp
imp.load_source('util', 'C:/full/path/foo/util.py')
import util
Relative
from . import mymodule
- Class
from .file import myClass
Absolute
Put your class in a package and use the future absolute_import. See rationale-for-absolute-imports
Example: the below unittest import will import the unittest of the system library, not the script itself
from __future__ import absolute_import
import unittest
Star
- Importing all functions of a module. Don't use to get no name resolution conflicts
from module import *
print sqrt(25)
What is the meaning of star ?
The import statement uses the following convention, if a package’s init.py code, the variable all is:
- defined, its value is taken to be the list of module names. Example with three modules:
__all__ = ["echo", "surround", "reverse"]
- is not defined, not import all submodules from the package into the current namespace; it only:
- ensures that the package has been imported (possibly running any initialization code in init.py)
- imports whatever names are defined in the package. This includes any names defined (and submodules explicitly loaded) by __init__.py.
- includes any submodules of the package that were explicitly loaded by previous import statements.
import sound.effects.echo
import sound.effects.surround
from sound.effects import *
In this example, the echo and surround modules are imported in the current namespace because they are defined in the sound.effects package when the from…import statement is executed. (This also works when __all__ is defined.)
Alias
- Module alias
import moduleName as alias
alias.func() # and not moduleName .funct()
- Name alias
from module import name as aliasName
Search
The import statement combines two operations;
- it searches for the named module,
- then it binds the results of that search to a name in the local scope.
To begin the search, Python needs the fully qualified name of the module (or package)
The name of the module are searched in the searchpath
Searchpath
The path is where Python searches the modules to Import.
Example
- package structure
spam/
__init__.py
foo.py
bar.py
from .foo import Foo
from .bar import Bar
then executing the following puts a name binding to foo and bar in the spam module:
import spam
spam.foo
<module 'spam.foo' from '/tmp/imports/spam/foo.py'>
spam.bar
<module 'spam.bar' from '/tmp/imports/spam/bar.py'>