rspec/rules/S2208/python/rule.adoc

== Why is this an issue?

Importing every public name from a module using a wildcard (``++from mymodule import *++``) is a bad idea because:

* It could lead to conflicts between names defined locally and the ones imported.
* It reduces code readability as developers will have a hard time knowing where names come from.
* It clutters the local namespace, which makes debugging more difficult.

Remember that imported names can change when you update your dependencies. A wildcard import that works today might be broken tomorrow.

=== Exceptions

No issue will be raised in ``++__init__.py++`` files. Wildcard imports are a common way of populating these modules.

No issue will be raised in modules doing only imports. Local modules are sometimes created as a proxy for third-party modules.

[source,python]
----
# file: mylibrary/pyplot.py
try:
    from guiqwt.pyplot import *  # Ok
except Exception:
    from matplotlib.pyplot import *  # Ok
----

Just keep in mind that wildcard imports might still create issues in these cases. It's always better to import only what you need.

== How to fix it

There are two ways to avoid a wildcard import:

* Replace it with `import mymodule` and access module members as `mymodule.myfunction`. If the module name is too long, alias it to a shorter name. Example: `import pandas as pd`
* List every imported name. If necessary import statements can be split on multiple lines using parentheses (preferred solution) or backslashes.

=== Code examples

==== Noncompliant code example

[source,python]
----
from math import *  # Noncompliant
def exp(x):
    pass
print(exp(0))   # "None" will be printed
----

==== Compliant solution

[source,python]
----
import math
def exp(x):
    pass
print(math.exp(0))   # "1.0" will be printed
----
Or

[source,python]
----
from math import exp as m_exp
def exp(x):
    pass
print(m_exp(0))   # "1.0" will be printed
----

== Resources

* https://docs.python.org/3.8/reference/simple_stmts.html#import[Python documentation - The import statement]

ifdef::env-github,rspecator-view[]

'''
== Implementation Specification
(visible only on this page)

=== Message

Import only needed names or import the module and then use its members.

=== Highlighting

* Primary: the whole import statement

'''
== Comments And Links
(visible only on this page)

=== on 23 Apr 2015, 09:36:39 Ann Campbell wrote:
\[~elena.vilchik] the docs.quantifiedcode.com link was 404. Would you supply the code samples, please?

=== on 23 Apr 2015, 10:16:47 Elena Vilchik wrote:
\[~ann.campbell.2] \http://webcache.googleusercontent.com/search?q=cache:JOuoj37QmGUJ:docs.quantifiedcode.com/python-code-patterns/maintainability/wildcard_import.html+&cd=3&hl=ru&ct=clnk&gl=fr here is saved copy. I don't know what happened :(

include::../comments-and-links.adoc[]

endif::env-github,rspecator-view[]