Unit variables upon their first appearance
Hello there, I have an idea for initializing a variable the first time it’s created; it can especially be helpful with containers, and dicts specifically. Let me demonstrate with some examples: Dic = {} # format fruit:count for fruit in fruits: If fruit in Dic: Dic[fruit]+=1 Else: Dic[fruit]=1 With my proposal, using := to init (similar to how in math parlance, the := is used for defining something for the first time) Dic = {} # format fruit:count For fruit in fruits: Dic[fruit]:= 0 Dic[fruit]+=1 Would be great to hear your feedback. Thanks. Moj
Hi Mirmojtaba, thanks for your suggestion. I doubt this idea will fly with this syntax because it could easily be confused with the walrus operator. x := 0 is *almost* legal syntax currently. In fact (x := 0) is legal, and it is quite possible that at some time in the future (Dic[fruit]:=0) will also be made legal. Your particular example can be written Dic = {} for fruit in fruits: Dic[fruit] = Dic.get(fruit, 0) + 1 # 0 is default value if key not in dict Actually I can see this idea being more useful with ordinary variables. At the moment we can write something like this: try: count = count + 1 except NameError: # count has not been initialised yet count = 1 which is fairly clumsy, and with your idea would be more concise: count := 0 # or a different syntax, maybe count <== 0 or something count += 1 (NB In fact if PEP 463 "Exception-catching expressions" had been accepted, we could write something like count = count + 1 except NameError: 1 but the PEP has been rejected, regrettably in my opinion. 🙁) That said, in most real examples, one could write count = 0 initially, and count = count +1 to increment. So I think it is up to you to provide further convincing examples in favour of your idea. Best wishes Rob Cliffe On 05/02/2022 20:18, Mirmojtaba Gharibi wrote:
On Sat, Feb 5, 2022, 12:19 PM Mirmojtaba Gharibi <mojtaba.gharibi@gmail.com> wrote:
To my eye, this does not look like a conditional assignment. And how would an operator like this work with objects other than dicts? Besides, it's easier and clearer to write this as dic = defaultdict(int) for fruit in fruits: dic[fruit] += 1 --- Bruce
Hi Mirmojtaba, thanks for your suggestion. I doubt this idea will fly with this syntax because it could easily be confused with the walrus operator. x := 0 is *almost* legal syntax currently. In fact (x := 0) is legal, and it is quite possible that at some time in the future (Dic[fruit]:=0) will also be made legal. Your particular example can be written Dic = {} for fruit in fruits: Dic[fruit] = Dic.get(fruit, 0) + 1 # 0 is default value if key not in dict Actually I can see this idea being more useful with ordinary variables. At the moment we can write something like this: try: count = count + 1 except NameError: # count has not been initialised yet count = 1 which is fairly clumsy, and with your idea would be more concise: count := 0 # or a different syntax, maybe count <== 0 or something count += 1 (NB In fact if PEP 463 "Exception-catching expressions" had been accepted, we could write something like count = count + 1 except NameError: 1 but the PEP has been rejected, regrettably in my opinion. 🙁) That said, in most real examples, one could write count = 0 initially, and count = count +1 to increment. So I think it is up to you to provide further convincing examples in favour of your idea. Best wishes Rob Cliffe On 05/02/2022 20:18, Mirmojtaba Gharibi wrote:
On Sat, Feb 5, 2022, 12:19 PM Mirmojtaba Gharibi <mojtaba.gharibi@gmail.com> wrote:
To my eye, this does not look like a conditional assignment. And how would an operator like this work with objects other than dicts? Besides, it's easier and clearer to write this as dic = defaultdict(int) for fruit in fruits: dic[fruit] += 1 --- Bruce
participants (4)
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Bruce Leban -
David Mertz, Ph.D. -
Mirmojtaba Gharibi -
Rob Cliffe