How Does 'import *' Actually Work in Python?

Unraveling the "import *" Enigma

What Does "import *" Import?

In Python, "import *" imports everything from the specified module into the current module. This allows direct access to the imported objects without prefixing them with the module name.

For example:

>>> from math import *
>>> pi
3.141592653589793
>>> sin(pi/2)
1.0

Caught in the Web of Name Collisions

However, importing "everything" with "*" is not recommended as it can create namespace collisions with existing variables or functions. Additionally, it may be inefficient if a significant number of objects are imported.

Explicitly Importing vs. Importing with "*"

It is preferable to explicitly import only the necessary objects:

>>> from math import pi
>>> pi
3.141592653589793
>>> sin(pi/2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'sin' is not defined

Alternatively, the module can be imported under its own namespace or alias:

>>> import math
>>> math.pi
3.141592653589793
>>> import math as m
>>> m.pi
3.141592653589793

Exceptions to the "* Import"

In certain cases, it may be appropriate to import everything with "". For instance, some libraries provide sub-modules specifically designed to be imported with "" and contain commonly used constants and functions.

Delving into the "* Import" Mechanism

With "import *", the following objects are imported:

• All names listed in the module's "__all__" variable (if defined).
• All names except those starting with an underscore ("_"), unless the "__all__" variable is defined.

Subtlety of Sub-modules

Contrary to common perception, "from xyz import " does not import sub-modules. Sub-modules must be explicitly imported separately, e.g. "from urllib.request import ".

The above is the detailed content of How Does 'import *' Actually Work in Python?. For more information, please follow other related articles on the PHP Chinese website!