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Excellent. That one belongs in any Python style guide. Though technically it's not a style, it does lead to better readability, and reduces the propensity for u

by teilo 16y ago

Excellent. That one belongs in any Python style guide. Though technically it's not a style, it does lead to better readability, and reduces the propensity for unforseen consequences.

jemfinch 16y ago
The reason it's not in the Python style guide is because it's a symptom of other problems in code. Lists are for holding multiple values of the same type. If you know that a list will always have one and only one value, it's not conceptually a list, it's some other type that's been encoded into a list for some reason, and you should fix that conceptual mismatch rather than papering over the issue with a style idiom.
- cturner 16y ago
  What you say sounds right, but it's not. Using some DB APIs you'll get back a list of results, and you'll know from the SQL that it will only have one result. Another example is if you know there is a single item in a data structure, and use list comprehension to extract it. You'll end up with a list of one item. These situations happen, and for good reasons.
- dochtman 16y ago
  We also commonly use tuples as light-weight types (a kind of heterogeneous collection).
- njharman 16y ago
  Lists use (not infrequently) logic like the following; If one element do this one element thing else do this more than one element thing
  - iron_ball 16y ago
    But in that case, either your code is evidently in a branch where the list will have one item -- as in your example -- in which case the context makes it clear. And if there's no context, such as in a nested function call, then at some point you should be passing that lone list item into a function which takes the item as an argument.
- teilo 16y ago
  That sounds logical enough, except for two things: First: You are often working with someone-else's library which for various reasons you cannot change. Second: It is not uncommon to use a standard method that may well be able to return multiple items, but in your use case it should only return one. Case in point: a database call that returns the result of a query.
  - baddox 16y ago
    Django's ORM, the only Python one I've experience with, provides get() for those cases.

by teilo 16y ago

Excellent. That one belongs in any Python style guide. Though technically it's not a style, it does lead to better readability, and reduces the propensity for unforseen consequences.

jemfinch 16y ago

The reason it's not in the Python style guide is because it's a symptom of other problems in code. Lists are for holding multiple values of the same type. If you know that a list will always have one and only one value, it's not conceptually a list, it's some other type that's been encoded into a list for some reason, and you should fix that conceptual mismatch rather than papering over the issue with a style idiom.

cturner 16y ago
What you say sounds right, but it's not. Using some DB APIs you'll get back a list of results, and you'll know from the SQL that it will only have one result. Another example is if you know there is a single item in a data structure, and use list comprehension to extract it. You'll end up with a list of one item. These situations happen, and for good reasons.
dochtman 16y ago
We also commonly use tuples as light-weight types (a kind of heterogeneous collection).
njharman 16y ago
Lists use (not infrequently) logic like the following; If one element do this one element thing else do this more than one element thing
- iron_ball 16y ago
  But in that case, either your code is evidently in a branch where the list will have one item -- as in your example -- in which case the context makes it clear. And if there's no context, such as in a nested function call, then at some point you should be passing that lone list item into a function which takes the item as an argument.
teilo 16y ago
That sounds logical enough, except for two things: First: You are often working with someone-else's library which for various reasons you cannot change. Second: It is not uncommon to use a standard method that may well be able to return multiple items, but in your use case it should only return one. Case in point: a database call that returns the result of a query.
- baddox 16y ago
  Django's ORM, the only Python one I've experience with, provides get() for those cases.