3 ms·

In Python3, you are really looking at... (func(a) for a in collection) map(func, collection) as equivalent. If you want a list (and not a generator),

by RMarcus 11y ago

In Python3, you are really looking at... (func(a) for a in collection) map(func, collection) as equivalent. If you want a list (and not a generator), you would need to do this: [func(a) for a in collection] list(map(func, collection)) For me, the first set (comprehensions) of notation has a more mathematical feel to it, i.e. { x^2 | x \in 0...10 }. Just replace the bar with "for" and it's almost the same thing. I believe the documentation for `filter` even mentions that it is equivalent to the comprehension[1]. [1] https://docs.python.org/3/library/functions.html#filter https://docs.python.org/3/library/functions.html#filter

jshen 11y ago
I've always found the list comprehension harder to read for non trivial examples. It may just be a matter of which a person learned first.
- dozzie 11y ago
  Not quite. I learned map and filter much earlier, and still I use more list comprehensions, both in Python and in Erlang.
- m_mueller 11y ago
  > It may just be a matter of which a person learned first. I think this is the case, for me map is much harder to read. But I also think that comprehensions go back to math sets, so I was familiar with this even before learning any programming. Therefore comprehensions clicked immediately for me and it's by far my favourite python feature.
  - hajile 11y ago
    I learned both around the same time, but even in good functional languages like Haskell, using a comprehension for anything more than simple problems results in an unreadable mess. map or filter are much easier to read for complex data manipulations and as a bonus, their composition rules make it easy to increase performance. For example, if you see two map functions together, you can wrap them in a compose and only map over your elements once. This isn't as immediately obvious when you're using comprehensions.
    - m_mueller 11y ago
      Could you give an example? Do you mean something like > [ manager.name for manager in set([ person.manager for person in employees ])] ? I assume with something like set() or unique() you need to create the intermediate iterable anyway, but without it I have trouble finding an example where doing a single list comprehension wouldn't suffice.

by RMarcus 11y ago

jshen 11y ago

I've always found the list comprehension harder to read for non trivial examples. It may just be a matter of which a person learned first.

dozzie 11y ago
Not quite. I learned map and filter much earlier, and still I use more list comprehensions, both in Python and in Erlang.
m_mueller 11y ago
> It may just be a matter of which a person learned first. I think this is the case, for me map is much harder to read. But I also think that comprehensions go back to math sets, so I was familiar with this even before learning any programming. Therefore comprehensions clicked immediately for me and it's by far my favourite python feature.
- hajile 11y ago
  I learned both around the same time, but even in good functional languages like Haskell, using a comprehension for anything more than simple problems results in an unreadable mess. map or filter are much easier to read for complex data manipulations and as a bonus, their composition rules make it easy to increase performance. For example, if you see two map functions together, you can wrap them in a compose and only map over your elements once. This isn't as immediately obvious when you're using comprehensions.
  - m_mueller 11y ago
    Could you give an example? Do you mean something like > [ manager.name for manager in set([ person.manager for person in employees ])] ? I assume with something like set() or unique() you need to create the intermediate iterable anyway, but without it I have trouble finding an example where doing a single list comprehension wouldn't suffice.