Idiom for long tuple unpacking [closed]

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Closed 5 years ago.

Scenario: you have a long tuple as a result of a SQL query and want to unpack it into individual values. What's the best way to do that while conforming to PEP8? So far I have these three options:

1. single assignment, use backslash to split to multiple lines

   person_id, first_name, last_name, email, \
       birth_date, graduation_year, home_street, \
       home_city, home_zip, mail_street, mail_city, \
       mail_zip = row
   

2. single assignment, group left-hand side in parantheses and break lines without a backslash

   (person_id, first_name, last_name, email,
       birth_date, graduation_year, home_street,
       home_city, home_zip, mail_street, mail_city,
       mail_zip) = row
   

3. split into multiple assignments, each fitting into a single line

   person_id, first_name, last_name, email = row[0:4]
   birth_date, graduation_year, home_street = row[4:7]
   home_city, home_zip, mail_street, mail_city = row[7:11]
   mail_zip = row[11]
   

Which of the three options is the best? Is there anything better?

回答1:

Anwering your question "Which of the three options is the best?"

pep8 states:

The preferred way of wrapping long lines is by using Python's implied line continuation inside parentheses, brackets and braces. Long lines can be broken over multiple lines by wrapping expressions in parentheses. These should be used in preference to using a backslash for line continuation.

This Means the second one is preferred over the first one. The third one is fine conforming pep8 as well, though personally wouldn't recommend it.

回答2:

To answer "is there anything better", I would suggest that a namedtuple allows you to access the individual data items with minimal fuss:

>>> from collections import namedtuple
>>> Person = namedtuple("Person", ['person_id', 'first_name', 'last_name', 
                                   'email', 'birth_date', 'graduation_year', 
                                   'home_street', 'home_city', 'home_zip', 
                                   'mail_street', 'mail_city', 'mail_zip'])
>>> row = range(12) # dummy data
>>> p = Person(*row) # unpack tuple into namedtuple
>>> p
Person(person_id=0, first_name=1, last_name=2, email=3, birth_date=4, graduation_year=5, home_street=6, home_city=7, home_zip=8, mail_street=9, mail_city=10, mail_zip=11)
>>> p.birth_date
4

This means you access attributes, rather than separate names, but is lighter-weight than building a class, keeps all of the data from your query together and exposes the values through sensible names.

来源：https://stackoverflow.com/questions/26036143/idiom-for-long-tuple-unpacking