Select all python variables with names starting with certain letters?

Question

I'm trying to add a number of variables, each a numpy array:

x = sum(d1 + d2 + d3 + d4... etc...)

Is there a way to just specify any variables with that string - d plus whatever number - should be included? Maybe there's a simple, slicing-style option? something like:

x = sum(d[1:])

In terms of creating a list, I would still have to compile all the arrays into a list, so my initial question - how to combine them based on name - still stands.

you can use `locals()` and regex, but as @Sayse said, it is better make a list — בנימין כהן, Oct 22 '20 at 10:07
i don't think such a thing is exist, and will be really curious to see it, but it seems that this is what lists and dictionaries built for... — adir abargil, Oct 22 '20 at 10:08
Does this answer your question? [How to get the value of a variable given its name in a string?](https://stackoverflow.com/questions/9437726/how-to-get-the-value-of-a-variable-given-its-name-in-a-string) — Tomerikoo, Oct 22 '20 at 10:23
Thanks for the replies. I edited my q to note that the variables are numpy arrays, not individual values, so I'd still have to combine them somehow. — Matthew Justin, Oct 22 '20 at 10:49

Alec · Accepted Answer · 2020-10-22T10:42:29.230

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Just make d a list

d = [d1, d2, ...]

def dval(num):
return d[num]

def dsum(lwr, upr, stp=1):
return sum(d[lwr:upr:stp])

edited Oct 22 '20 at 10:42

answered Oct 22 '20 at 10:08

Alec

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it doesnt seems like what he is looking for – adir abargil Oct 22 '20 at 10:09
I edited my original post, but I believe even if I made the variables - all numpy arrays - into a list I'd still need a way to combine them. – Matthew Justin Oct 22 '20 at 10:50

adir abargil · Answer 2 · 2020-10-22T10:17:49.810

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as @בינימין כהן said you can use locals() for this specific task even tought it is more recommended to use lists in this scenario, use it just like this for your case:

your_d_vars = [val for key,val in  locals().items() if key[0] == 'd' and key[1:].isdigit()]
x = sum(your_d_vars )

edited Oct 22 '20 at 10:17

answered Oct 22 '20 at 10:15

adir abargil

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and then `x = sum(your_d_vars)` – lunesco Oct 22 '20 at 10:17
Can also use regex for the variable name: `if re.match(r"d\d+", key)` – Tomerikoo Oct 22 '20 at 10:19
is your regex confirm the rest of the words are digits? – adir abargil Oct 22 '20 at 10:20
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While this technically does what the question asked for, it's a terrible approach for addressing the underlying goal. Making a list instead of numbered variables is a much better approach. – user2357112 Oct 22 '20 at 10:21
i meantioned what you said in my answer... yet people might still find it usefull.... – adir abargil Oct 22 '20 at 10:22
Yes, the first `d` is literal letter `"d"`, then `\d` is a short-hand for numbers, equivalent to `[0-9]`, then the `+` just means *at least one* – Tomerikoo Oct 22 '20 at 10:24

score 0 · Answer 3 · answered Oct 22 '20 at 10:22

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According to this thread, you can, in fact, obtain a variable by a string. As such, you could do something such as the following:

d1 = 4
d2 = 5
d3 = 6
d4 = 7

sum = 0
for i in range(1, 5):
    sum += globals()['d'+str(i)] # build string of the variables you want to access

print(sum) # prints 22

Note: d1, d2, d3, d4 ... must be global variables. Please see the linked thread for more information and other options if necessary.

answered Oct 22 '20 at 10:22

Matthew Knill

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If the answer exists in another question already, it should be flagged as a duplicate (as I already did...) – Tomerikoo Oct 22 '20 at 10:25

Select all python variables with names starting with certain letters?

3 Answers3