Star / Wildcard imports

Last Updated: February 3, 2018 12:20 PM UTC

Last edited by:

Joseph <joseph@josephbanks.me>

Initial Commit

THIS IS FAKE DEMO DATA

Wildcard imports are import statements in the form from <module_name> import *. What imports like these do is that they import everything [1] from the module into the current module's namespace [2]. This allows you to use names defined in the imported module without prefixing the module's name.

Example:

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

This is discouraged, for various reasons:

Example:

>>> from custom_sin import sin
>>> from math import *
>>> sin(pi / 2)  # uses sin from math rather than your custom sin

- Potential namespace collision. Names defined from a previous import might get shadowed by a wildcard import. - Causes ambiguity. From the example, it is unclear which sin function is actually being used. From the Zen of Python [3]: Explicit is better than implicit. - Makes import order significant, which they shouldn't. Certain IDE's sort import functionality may end up breaking code due to namespace collision.

How should you import?

• Import the module under the module's namespace (Only import the name of the module, and names defined in the module can be used by prefixing the module's name)

  >>> import math
  >>> math.sin(math.pi / 2)

• Explicitly import certain names from the module

  >>> from math import sin, pi
  >>> sin(pi / 2)

  Conclusion: Namespaces are one honking great idea -- let's do more of those! [3]

[1] If the module defines the variable __all__, the names defined in __all__ will get imported by the wildcard import, otherwise all the names in the module get imported (except for names with a leading underscore) [2] Namespaces and scopes [3] Zen of Python