I was grateful for the example of multilined strings, mysterious as it is. The lack of any way to do this has been an annoyance of mine for quite some time.
Python idioms I wish I'd learned earlier
11–20 of 174 posts
Re: Python idioms I wish I'd learned earlier
#12I'm not much of a Python guy, but that chained comparison operator is sweet! Sure, it's just syntax sugar, but it saves a lot of keystrokes, especially if the variable name is long. Is Python the only language with this feature?
Perl6 has it too
> perl6
> 3 Re: Python idioms I wish I'd learned earlier
#13One of my favorites: >>> print "* "* 50 to quickly print a separator on my terminal :) Previous discussion on python idioms from 300 days ago: https://news.ycombinator.com/item?id=7151433
That's cute, but the result of a bad design decision.
Python overloads "+" as concatenate for strings. This also applies to lists. So
[1,2,3] + [4,5,6] yields [1,2,3,4,5,6]
Then, viewing multiplication as repeated addition, Python gives us
[1,2,3]*4 yields [1, 2, 3, 1, 2, 3, 1, 2, 3, 1, 2, 3]
Then there's numpy, which has its own array type, needed because Python's array math is slow. Numpy arrays have different semantics - add and multiply perform the usual numeric operations. You can mix numpy arrays and built-in lists with "+" and "*". Mixed expressions are evaluated using numpy's semantics. Since Python doesn't have type checking, it's possible to pass the wrong kind of numeric array to a function and have it treated with the wrong semantics.
Moral: when designing your language, using "+" for concatenation is tempting, but generalizing that concept comes back to bite you.
Re: Python idioms I wish I'd learned earlier
#14I'm not much of a Python guy, but that chained comparison operator is sweet! Sure, it's just syntax sugar, but it saves a lot of keystrokes, especially if the variable name is long. Is Python the only language with this feature?
Common Lisp (and other dialects):
( (lcm a b c d ...) ;; lowest common multiple
(+) -> 0
(+ a) -> a
(+ a b) -> a + b
(+ a b c) -> (a + b) + c
(*) -> 1
(* a) -> a
(* a b) -> a * b
(* a b c) -> (a * b) * c
(and ( (Re: Python idioms I wish I'd learned earlier
#15I'm not much of a Python guy, but that chained comparison operator is sweet! Sure, it's just syntax sugar, but it saves a lot of keystrokes, especially if the variable name is long. Is Python the only language with this feature?
I'm not sure if other languages have it, but I have to say that pycharm is excellent at suggesting chained comparisons to you. I didn't know this existed before I switched IDEs. if 2 > 3 and 2 becomes if 3 < 2 < 7
If this Pycharm really had brains it would tell you that (2>3 and 2<7) reduces to (false and true), to false, at compile time, so the code wrapped in the if is unreachable.
Re: Python idioms I wish I'd learned earlier
#16One of my favorites: >>> print "* "* 50 to quickly print a separator on my terminal :) Previous discussion on python idioms from 300 days ago: https://news.ycombinator.com/item?id=7151433
That's cute, but the result of a bad design decision. Python overloads "+" as concatenate for strings. This also applies to lists. So [1,2,3] + [4,5,6] yields [1,2,3,4,5,6] This is cute, but not what you want for numerical work. Then, viewing multiplication as repeated addition, Python gives us [1,2,3]*4 yields [1, 2, 3, 1, 2, 3, 1, 2, 3, 1, 2, 3] This is rarely what was wanted. Then there's numpy, which has its own…
Then what would you have
[1,2,'q',[1,('a',2)]] + 4
Re: Python idioms I wish I'd learned earlier
#17One of my favorites: >>> print "* "* 50 to quickly print a separator on my terminal :) Previous discussion on python idioms from 300 days ago: https://news.ycombinator.com/item?id=7151433
That's cute, but the result of a bad design decision. Python overloads "+" as concatenate for strings. This also applies to lists. So [1,2,3] + [4,5,6] yields [1,2,3,4,5,6] This is cute, but not what you want for numerical work. Then, viewing multiplication as repeated addition, Python gives us [1,2,3]*4 yields [1, 2, 3, 1, 2, 3, 1, 2, 3, 1, 2, 3] This is rarely what was wanted. Then there's numpy, which has its own…
"This is rarely what was wanted."
I don't know what else you would have expected...
Re: Python idioms I wish I'd learned earlier
#18I'm not much of a Python guy, but that chained comparison operator is sweet! Sure, it's just syntax sugar, but it saves a lot of keystrokes, especially if the variable name is long. Is Python the only language with this feature?
Common Lisp (and other dialects): ( Also: (lcm a b c d ...) ;; lowest common multiple (+) -> 0 (+ a) -> a (+ a b) -> a + b (+ a b c) -> (a + b) + c (*) -> 1 (* a) -> a (* a b) -> a * b (* a b c) -> (a * b) * c Is it just syntactic sugar? ( (and ( isn't the same as ( By the way, this could be turned into a short-circuiting operator: more semantic variation. Suppose < is allowed to control evaluation. Then an expressio…
But can any lisp dialect do:
a = c
?Re: Python idioms I wish I'd learned earlier
#19One of my favorites: >>> print "* "* 50 to quickly print a separator on my terminal :) Previous discussion on python idioms from 300 days ago: https://news.ycombinator.com/item?id=7151433
That's cute, but the result of a bad design decision. Python overloads "+" as concatenate for strings. This also applies to lists. So [1,2,3] + [4,5,6] yields [1,2,3,4,5,6] This is cute, but not what you want for numerical work. Then, viewing multiplication as repeated addition, Python gives us [1,2,3]*4 yields [1, 2, 3, 1, 2, 3, 1, 2, 3, 1, 2, 3] This is rarely what was wanted. Then there's numpy, which has its own…
[deleted]
Re: Python idioms I wish I'd learned earlier
#20Earlier quoted context omitted.
That's cute, but the result of a bad design decision. Python overloads "+" as concatenate for strings. This also applies to lists. So [1,2,3] + [4,5,6] yields [1,2,3,4,5,6] This is cute, but not what you want for numerical work. Then, viewing multiplication as repeated addition, Python gives us [1,2,3]*4 yields [1, 2, 3, 1, 2, 3, 1, 2, 3, 1, 2, 3] This is rarely what was wanted. Then there's numpy, which has its own…
Then what would you have [1,2,'q',[1,('a',2)]] + 4 yield? The reason why numpy lets you do math operation on each element in an array is because you can safely assume that each element is a number. You can assume absolutely nothing about the types of the elements in a list.
"TypeError: cannot add 'str' and 'int' objects."
Just because you can define semantics for nonsense doesn't mean you should.