63e5b7219b
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97 lines
2.8 KiB
Plaintext
97 lines
2.8 KiB
Plaintext
== Why is this an issue?
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Importing every public name from a module using a wildcard (``++from mymodule import *++``) is a bad idea because:
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* It could lead to conflicts between names defined locally and the ones imported.
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* It reduces code readability as developers will have a hard time knowing where names come from.
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* It clutters the local namespace, which makes debugging more difficult.
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Remember that imported names can change when you update your dependencies. A wildcard import that works today might be broken tomorrow.
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=== Exceptions
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No issue will be raised in ``++__init__.py++`` files. Wildcard imports are a common way of populating these modules.
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No issue will be raised in modules doing only imports. Local modules are sometimes created as a proxy for third-party modules.
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[source,python]
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----
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# file: mylibrary/pyplot.py
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try:
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from guiqwt.pyplot import * # Ok
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except Exception:
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from matplotlib.pyplot import * # Ok
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----
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Just keep in mind that wildcard imports might still create issues in these cases. It's always better to import only what you need.
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== How to fix it
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There are two ways to avoid a wildcard import:
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* 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`
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* List every imported name. If necessary import statements can be split on multiple lines using parentheses (preferred solution) or backslashes.
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=== Code examples
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==== Noncompliant code example
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[source,python]
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----
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from math import * # Noncompliant
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def exp(x):
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pass
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print(exp(0)) # "None" will be printed
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----
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==== Compliant solution
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[source,python]
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----
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import math
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def exp(x):
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pass
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print(math.exp(0)) # "1.0" will be printed
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----
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Or
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[source,python]
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----
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from math import exp as m_exp
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def exp(x):
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pass
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print(m_exp(0)) # "1.0" will be printed
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----
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== Resources
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* https://docs.python.org/3.8/reference/simple_stmts.html#import[Python documentation - The import statement]
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ifdef::env-github,rspecator-view[]
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'''
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== Implementation Specification
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(visible only on this page)
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=== Message
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Import only needed names or import the module and then use its members.
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=== Highlighting
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* Primary: the whole import statement
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'''
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== Comments And Links
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(visible only on this page)
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=== on 23 Apr 2015, 09:36:39 Ann Campbell wrote:
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\[~elena.vilchik] the docs.quantifiedcode.com link was 404. Would you supply the code samples, please?
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=== on 23 Apr 2015, 10:16:47 Elena Vilchik wrote:
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\[~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 :(
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include::../comments-and-links.adoc[]
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endif::env-github,rspecator-view[]
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